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linux/kernel/bpf/verifier.c
Alexei Starovoitov 1b9b69ecb3 bpf: teach verifier to recognize imm += ptr pattern 
Humans don't write C code like:
  u8 *ptr = skb->data;
  int imm = 4;
  imm += ptr;
but from llvm backend point of view 'imm' and 'ptr' are registers and
imm += ptr may be preferred vs ptr += imm depending which register value
will be used further in the code, while verifier can only recognize ptr += imm.
That caused small unrelated changes in the C code of the bpf program to
trigger rejection by the verifier. Therefore teach the verifier to recognize
both ptr += imm and imm += ptr.
For example:
when R6=pkt(id=0,off=0,r=62) R7=imm22
after r7 += r6 instruction
will be R6=pkt(id=0,off=0,r=62) R7=pkt(id=0,off=22,r=62)

Fixes: 969bf05eb3 ("bpf: direct packet access")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-20 19:53:03 -04:00

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/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
* Copyright (c) 2016 Facebook
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*/
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <net/netlink.h>
#include <linux/file.h>
#include <linux/vmalloc.h>
/* bpf_check() is a static code analyzer that walks eBPF program
* instruction by instruction and updates register/stack state.
* All paths of conditional branches are analyzed until 'bpf_exit' insn.
*
* The first pass is depth-first-search to check that the program is a DAG.
* It rejects the following programs:
* - larger than BPF_MAXINSNS insns
* - if loop is present (detected via back-edge)
* - unreachable insns exist (shouldn't be a forest. program = one function)
* - out of bounds or malformed jumps
* The second pass is all possible path descent from the 1st insn.
* Since it's analyzing all pathes through the program, the length of the
* analysis is limited to 32k insn, which may be hit even if total number of
* insn is less then 4K, but there are too many branches that change stack/regs.
* Number of 'branches to be analyzed' is limited to 1k
*
* On entry to each instruction, each register has a type, and the instruction
* changes the types of the registers depending on instruction semantics.
* If instruction is BPF_MOV64_REG(BPF_REG_1, BPF_REG_5), then type of R5 is
* copied to R1.
*
* All registers are 64-bit.
* R0 - return register
* R1-R5 argument passing registers
* R6-R9 callee saved registers
* R10 - frame pointer read-only
*
* At the start of BPF program the register R1 contains a pointer to bpf_context
* and has type PTR_TO_CTX.
*
* Verifier tracks arithmetic operations on pointers in case:
* BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
* BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -20),
* 1st insn copies R10 (which has FRAME_PTR) type into R1
* and 2nd arithmetic instruction is pattern matched to recognize
* that it wants to construct a pointer to some element within stack.
* So after 2nd insn, the register R1 has type PTR_TO_STACK
* (and -20 constant is saved for further stack bounds checking).
* Meaning that this reg is a pointer to stack plus known immediate constant.
*
* Most of the time the registers have UNKNOWN_VALUE type, which
* means the register has some value, but it's not a valid pointer.
* (like pointer plus pointer becomes UNKNOWN_VALUE type)
*
* When verifier sees load or store instructions the type of base register
* can be: PTR_TO_MAP_VALUE, PTR_TO_CTX, FRAME_PTR. These are three pointer
* types recognized by check_mem_access() function.
*
* PTR_TO_MAP_VALUE means that this register is pointing to 'map element value'
* and the range of [ptr, ptr + map's value_size) is accessible.
*
* registers used to pass values to function calls are checked against
* function argument constraints.
*
* ARG_PTR_TO_MAP_KEY is one of such argument constraints.
* It means that the register type passed to this function must be
* PTR_TO_STACK and it will be used inside the function as
* 'pointer to map element key'
*
* For example the argument constraints for bpf_map_lookup_elem():
* .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
* .arg1_type = ARG_CONST_MAP_PTR,
* .arg2_type = ARG_PTR_TO_MAP_KEY,
*
* ret_type says that this function returns 'pointer to map elem value or null'
* function expects 1st argument to be a const pointer to 'struct bpf_map' and
* 2nd argument should be a pointer to stack, which will be used inside
* the helper function as a pointer to map element key.
*
* On the kernel side the helper function looks like:
* u64 bpf_map_lookup_elem(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
* {
* struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
* void *key = (void *) (unsigned long) r2;
* void *value;
*
* here kernel can access 'key' and 'map' pointers safely, knowing that
* [key, key + map->key_size) bytes are valid and were initialized on
* the stack of eBPF program.
* }
*
* Corresponding eBPF program may look like:
* BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), // after this insn R2 type is FRAME_PTR
* BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), // after this insn R2 type is PTR_TO_STACK
* BPF_LD_MAP_FD(BPF_REG_1, map_fd), // after this insn R1 type is CONST_PTR_TO_MAP
* BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
* here verifier looks at prototype of map_lookup_elem() and sees:
* .arg1_type == ARG_CONST_MAP_PTR and R1->type == CONST_PTR_TO_MAP, which is ok,
* Now verifier knows that this map has key of R1->map_ptr->key_size bytes
*
* Then .arg2_type == ARG_PTR_TO_MAP_KEY and R2->type == PTR_TO_STACK, ok so far,
* Now verifier checks that [R2, R2 + map's key_size) are within stack limits
* and were initialized prior to this call.
* If it's ok, then verifier allows this BPF_CALL insn and looks at
* .ret_type which is RET_PTR_TO_MAP_VALUE_OR_NULL, so it sets
* R0->type = PTR_TO_MAP_VALUE_OR_NULL which means bpf_map_lookup_elem() function
* returns ether pointer to map value or NULL.
*
* When type PTR_TO_MAP_VALUE_OR_NULL passes through 'if (reg != 0) goto +off'
* insn, the register holding that pointer in the true branch changes state to
* PTR_TO_MAP_VALUE and the same register changes state to CONST_IMM in the false
* branch. See check_cond_jmp_op().
*
* After the call R0 is set to return type of the function and registers R1-R5
* are set to NOT_INIT to indicate that they are no longer readable.
*/
/* types of values stored in eBPF registers */
enum bpf_reg_type {
NOT_INIT = 0, /* nothing was written into register */
UNKNOWN_VALUE, /* reg doesn't contain a valid pointer */
PTR_TO_CTX, /* reg points to bpf_context */
CONST_PTR_TO_MAP, /* reg points to struct bpf_map */
PTR_TO_MAP_VALUE, /* reg points to map element value */
PTR_TO_MAP_VALUE_OR_NULL,/* points to map elem value or NULL */
FRAME_PTR, /* reg == frame_pointer */
PTR_TO_STACK, /* reg == frame_pointer + imm */
CONST_IMM, /* constant integer value */
/* PTR_TO_PACKET represents:
* skb->data
* skb->data + imm
* skb->data + (u16) var
* skb->data + (u16) var + imm
* if (range > 0) then [ptr, ptr + range - off) is safe to access
* if (id > 0) means that some 'var' was added
* if (off > 0) menas that 'imm' was added
*/
PTR_TO_PACKET,
PTR_TO_PACKET_END, /* skb->data + headlen */
};
struct reg_state {
enum bpf_reg_type type;
union {
/* valid when type == CONST_IMM | PTR_TO_STACK | UNKNOWN_VALUE */
s64 imm;
/* valid when type == PTR_TO_PACKET* */
struct {
u32 id;
u16 off;
u16 range;
};
/* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
* PTR_TO_MAP_VALUE_OR_NULL
*/
struct bpf_map *map_ptr;
};
};
enum bpf_stack_slot_type {
STACK_INVALID, /* nothing was stored in this stack slot */
STACK_SPILL, /* register spilled into stack */
STACK_MISC /* BPF program wrote some data into this slot */
};
#define BPF_REG_SIZE 8 /* size of eBPF register in bytes */
/* state of the program:
* type of all registers and stack info
*/
struct verifier_state {
struct reg_state regs[MAX_BPF_REG];
u8 stack_slot_type[MAX_BPF_STACK];
struct reg_state spilled_regs[MAX_BPF_STACK / BPF_REG_SIZE];
};
/* linked list of verifier states used to prune search */
struct verifier_state_list {
struct verifier_state state;
struct verifier_state_list *next;
};
/* verifier_state + insn_idx are pushed to stack when branch is encountered */
struct verifier_stack_elem {
/* verifer state is 'st'
* before processing instruction 'insn_idx'
* and after processing instruction 'prev_insn_idx'
*/
struct verifier_state st;
int insn_idx;
int prev_insn_idx;
struct verifier_stack_elem *next;
};
#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
/* single container for all structs
* one verifier_env per bpf_check() call
*/
struct verifier_env {
struct bpf_prog *prog; /* eBPF program being verified */
struct verifier_stack_elem *head; /* stack of verifier states to be processed */
int stack_size; /* number of states to be processed */
struct verifier_state cur_state; /* current verifier state */
struct verifier_state_list **explored_states; /* search pruning optimization */
struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
u32 used_map_cnt; /* number of used maps */
bool allow_ptr_leaks;
};
#define BPF_COMPLEXITY_LIMIT_INSNS 65536
#define BPF_COMPLEXITY_LIMIT_STACK 1024
struct bpf_call_arg_meta {
struct bpf_map *map_ptr;
bool raw_mode;
int regno;
int access_size;
};
/* verbose verifier prints what it's seeing
* bpf_check() is called under lock, so no race to access these global vars
*/
static u32 log_level, log_size, log_len;
static char *log_buf;
static DEFINE_MUTEX(bpf_verifier_lock);
/* log_level controls verbosity level of eBPF verifier.
* verbose() is used to dump the verification trace to the log, so the user
* can figure out what's wrong with the program
*/
static __printf(1, 2) void verbose(const char *fmt, ...)
{
va_list args;
if (log_level == 0 || log_len >= log_size - 1)
return;
va_start(args, fmt);
log_len += vscnprintf(log_buf + log_len, log_size - log_len, fmt, args);
va_end(args);
}
/* string representation of 'enum bpf_reg_type' */
static const char * const reg_type_str[] = {
[NOT_INIT] = "?",
[UNKNOWN_VALUE] = "inv",
[PTR_TO_CTX] = "ctx",
[CONST_PTR_TO_MAP] = "map_ptr",
[PTR_TO_MAP_VALUE] = "map_value",
[PTR_TO_MAP_VALUE_OR_NULL] = "map_value_or_null",
[FRAME_PTR] = "fp",
[PTR_TO_STACK] = "fp",
[CONST_IMM] = "imm",
[PTR_TO_PACKET] = "pkt",
[PTR_TO_PACKET_END] = "pkt_end",
};
static void print_verifier_state(struct verifier_state *state)
{
struct reg_state *reg;
enum bpf_reg_type t;
int i;
for (i = 0; i < MAX_BPF_REG; i++) {
reg = &state->regs[i];
t = reg->type;
if (t == NOT_INIT)
continue;
verbose(" R%d=%s", i, reg_type_str[t]);
if (t == CONST_IMM || t == PTR_TO_STACK)
verbose("%lld", reg->imm);
else if (t == PTR_TO_PACKET)
verbose("(id=%d,off=%d,r=%d)",
reg->id, reg->off, reg->range);
else if (t == UNKNOWN_VALUE && reg->imm)
verbose("%lld", reg->imm);
else if (t == CONST_PTR_TO_MAP || t == PTR_TO_MAP_VALUE ||
t == PTR_TO_MAP_VALUE_OR_NULL)
verbose("(ks=%d,vs=%d)",
reg->map_ptr->key_size,
reg->map_ptr->value_size);
}
for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
if (state->stack_slot_type[i] == STACK_SPILL)
verbose(" fp%d=%s", -MAX_BPF_STACK + i,
reg_type_str[state->spilled_regs[i / BPF_REG_SIZE].type]);
}
verbose("\n");
}
static const char *const bpf_class_string[] = {
[BPF_LD] = "ld",
[BPF_LDX] = "ldx",
[BPF_ST] = "st",
[BPF_STX] = "stx",
[BPF_ALU] = "alu",
[BPF_JMP] = "jmp",
[BPF_RET] = "BUG",
[BPF_ALU64] = "alu64",
};
static const char *const bpf_alu_string[16] = {
[BPF_ADD >> 4] = "+=",
[BPF_SUB >> 4] = "-=",
[BPF_MUL >> 4] = "*=",
[BPF_DIV >> 4] = "/=",
[BPF_OR >> 4] = "|=",
[BPF_AND >> 4] = "&=",
[BPF_LSH >> 4] = "<<=",
[BPF_RSH >> 4] = ">>=",
[BPF_NEG >> 4] = "neg",
[BPF_MOD >> 4] = "%=",
[BPF_XOR >> 4] = "^=",
[BPF_MOV >> 4] = "=",
[BPF_ARSH >> 4] = "s>>=",
[BPF_END >> 4] = "endian",
};
static const char *const bpf_ldst_string[] = {
[BPF_W >> 3] = "u32",
[BPF_H >> 3] = "u16",
[BPF_B >> 3] = "u8",
[BPF_DW >> 3] = "u64",
};
static const char *const bpf_jmp_string[16] = {
[BPF_JA >> 4] = "jmp",
[BPF_JEQ >> 4] = "==",
[BPF_JGT >> 4] = ">",
[BPF_JGE >> 4] = ">=",
[BPF_JSET >> 4] = "&",
[BPF_JNE >> 4] = "!=",
[BPF_JSGT >> 4] = "s>",
[BPF_JSGE >> 4] = "s>=",
[BPF_CALL >> 4] = "call",
[BPF_EXIT >> 4] = "exit",
};
static void print_bpf_insn(struct bpf_insn *insn)
{
u8 class = BPF_CLASS(insn->code);
if (class == BPF_ALU || class == BPF_ALU64) {
if (BPF_SRC(insn->code) == BPF_X)
verbose("(%02x) %sr%d %s %sr%d\n",
insn->code, class == BPF_ALU ? "(u32) " : "",
insn->dst_reg,
bpf_alu_string[BPF_OP(insn->code) >> 4],
class == BPF_ALU ? "(u32) " : "",
insn->src_reg);
else
verbose("(%02x) %sr%d %s %s%d\n",
insn->code, class == BPF_ALU ? "(u32) " : "",
insn->dst_reg,
bpf_alu_string[BPF_OP(insn->code) >> 4],
class == BPF_ALU ? "(u32) " : "",
insn->imm);
} else if (class == BPF_STX) {
if (BPF_MODE(insn->code) == BPF_MEM)
verbose("(%02x) *(%s *)(r%d %+d) = r%d\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->dst_reg,
insn->off, insn->src_reg);
else if (BPF_MODE(insn->code) == BPF_XADD)
verbose("(%02x) lock *(%s *)(r%d %+d) += r%d\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->dst_reg, insn->off,
insn->src_reg);
else
verbose("BUG_%02x\n", insn->code);
} else if (class == BPF_ST) {
if (BPF_MODE(insn->code) != BPF_MEM) {
verbose("BUG_st_%02x\n", insn->code);
return;
}
verbose("(%02x) *(%s *)(r%d %+d) = %d\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->dst_reg,
insn->off, insn->imm);
} else if (class == BPF_LDX) {
if (BPF_MODE(insn->code) != BPF_MEM) {
verbose("BUG_ldx_%02x\n", insn->code);
return;
}
verbose("(%02x) r%d = *(%s *)(r%d %+d)\n",
insn->code, insn->dst_reg,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->src_reg, insn->off);
} else if (class == BPF_LD) {
if (BPF_MODE(insn->code) == BPF_ABS) {
verbose("(%02x) r0 = *(%s *)skb[%d]\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->imm);
} else if (BPF_MODE(insn->code) == BPF_IND) {
verbose("(%02x) r0 = *(%s *)skb[r%d + %d]\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->src_reg, insn->imm);
} else if (BPF_MODE(insn->code) == BPF_IMM) {
verbose("(%02x) r%d = 0x%x\n",
insn->code, insn->dst_reg, insn->imm);
} else {
verbose("BUG_ld_%02x\n", insn->code);
return;
}
} else if (class == BPF_JMP) {
u8 opcode = BPF_OP(insn->code);
if (opcode == BPF_CALL) {
verbose("(%02x) call %d\n", insn->code, insn->imm);
} else if (insn->code == (BPF_JMP | BPF_JA)) {
verbose("(%02x) goto pc%+d\n",
insn->code, insn->off);
} else if (insn->code == (BPF_JMP | BPF_EXIT)) {
verbose("(%02x) exit\n", insn->code);
} else if (BPF_SRC(insn->code) == BPF_X) {
verbose("(%02x) if r%d %s r%d goto pc%+d\n",
insn->code, insn->dst_reg,
bpf_jmp_string[BPF_OP(insn->code) >> 4],
insn->src_reg, insn->off);
} else {
verbose("(%02x) if r%d %s 0x%x goto pc%+d\n",
insn->code, insn->dst_reg,
bpf_jmp_string[BPF_OP(insn->code) >> 4],
insn->imm, insn->off);
}
} else {
verbose("(%02x) %s\n", insn->code, bpf_class_string[class]);
}
}
static int pop_stack(struct verifier_env *env, int *prev_insn_idx)
{
struct verifier_stack_elem *elem;
int insn_idx;
if (env->head == NULL)
return -1;
memcpy(&env->cur_state, &env->head->st, sizeof(env->cur_state));
insn_idx = env->head->insn_idx;
if (prev_insn_idx)
*prev_insn_idx = env->head->prev_insn_idx;
elem = env->head->next;
kfree(env->head);
env->head = elem;
env->stack_size--;
return insn_idx;
}
static struct verifier_state *push_stack(struct verifier_env *env, int insn_idx,
int prev_insn_idx)
{
struct verifier_stack_elem *elem;
elem = kmalloc(sizeof(struct verifier_stack_elem), GFP_KERNEL);
if (!elem)
goto err;
memcpy(&elem->st, &env->cur_state, sizeof(env->cur_state));
elem->insn_idx = insn_idx;
elem->prev_insn_idx = prev_insn_idx;
elem->next = env->head;
env->head = elem;
env->stack_size++;
if (env->stack_size > BPF_COMPLEXITY_LIMIT_STACK) {
verbose("BPF program is too complex\n");
goto err;
}
return &elem->st;
err:
/* pop all elements and return */
while (pop_stack(env, NULL) >= 0);
return NULL;
}
#define CALLER_SAVED_REGS 6
static const int caller_saved[CALLER_SAVED_REGS] = {
BPF_REG_0, BPF_REG_1, BPF_REG_2, BPF_REG_3, BPF_REG_4, BPF_REG_5
};
static void init_reg_state(struct reg_state *regs)
{
int i;
for (i = 0; i < MAX_BPF_REG; i++) {
regs[i].type = NOT_INIT;
regs[i].imm = 0;
}
/* frame pointer */
regs[BPF_REG_FP].type = FRAME_PTR;
/* 1st arg to a function */
regs[BPF_REG_1].type = PTR_TO_CTX;
}
static void mark_reg_unknown_value(struct reg_state *regs, u32 regno)
{
BUG_ON(regno >= MAX_BPF_REG);
regs[regno].type = UNKNOWN_VALUE;
regs[regno].imm = 0;
}
enum reg_arg_type {
SRC_OP, /* register is used as source operand */
DST_OP, /* register is used as destination operand */
DST_OP_NO_MARK /* same as above, check only, don't mark */
};
static int check_reg_arg(struct reg_state *regs, u32 regno,
enum reg_arg_type t)
{
if (regno >= MAX_BPF_REG) {
verbose("R%d is invalid\n", regno);
return -EINVAL;
}
if (t == SRC_OP) {
/* check whether register used as source operand can be read */
if (regs[regno].type == NOT_INIT) {
verbose("R%d !read_ok\n", regno);
return -EACCES;
}
} else {
/* check whether register used as dest operand can be written to */
if (regno == BPF_REG_FP) {
verbose("frame pointer is read only\n");
return -EACCES;
}
if (t == DST_OP)
mark_reg_unknown_value(regs, regno);
}
return 0;
}
static int bpf_size_to_bytes(int bpf_size)
{
if (bpf_size == BPF_W)
return 4;
else if (bpf_size == BPF_H)
return 2;
else if (bpf_size == BPF_B)
return 1;
else if (bpf_size == BPF_DW)
return 8;
else
return -EINVAL;
}
static bool is_spillable_regtype(enum bpf_reg_type type)
{
switch (type) {
case PTR_TO_MAP_VALUE:
case PTR_TO_MAP_VALUE_OR_NULL:
case PTR_TO_STACK:
case PTR_TO_CTX:
case PTR_TO_PACKET:
case PTR_TO_PACKET_END:
case FRAME_PTR:
case CONST_PTR_TO_MAP:
return true;
default:
return false;
}
}
/* check_stack_read/write functions track spill/fill of registers,
* stack boundary and alignment are checked in check_mem_access()
*/
static int check_stack_write(struct verifier_state *state, int off, int size,
int value_regno)
{
int i;
/* caller checked that off % size == 0 and -MAX_BPF_STACK <= off < 0,
* so it's aligned access and [off, off + size) are within stack limits
*/
if (value_regno >= 0 &&
is_spillable_regtype(state->regs[value_regno].type)) {
/* register containing pointer is being spilled into stack */
if (size != BPF_REG_SIZE) {
verbose("invalid size of register spill\n");
return -EACCES;
}
/* save register state */
state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE] =
state->regs[value_regno];
for (i = 0; i < BPF_REG_SIZE; i++)
state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_SPILL;
} else {
/* regular write of data into stack */
state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE] =
(struct reg_state) {};
for (i = 0; i < size; i++)
state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_MISC;
}
return 0;
}
static int check_stack_read(struct verifier_state *state, int off, int size,
int value_regno)
{
u8 *slot_type;
int i;
slot_type = &state->stack_slot_type[MAX_BPF_STACK + off];
if (slot_type[0] == STACK_SPILL) {
if (size != BPF_REG_SIZE) {
verbose("invalid size of register spill\n");
return -EACCES;
}
for (i = 1; i < BPF_REG_SIZE; i++) {
if (slot_type[i] != STACK_SPILL) {
verbose("corrupted spill memory\n");
return -EACCES;
}
}
if (value_regno >= 0)
/* restore register state from stack */
state->regs[value_regno] =
state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE];
return 0;
} else {
for (i = 0; i < size; i++) {
if (slot_type[i] != STACK_MISC) {
verbose("invalid read from stack off %d+%d size %d\n",
off, i, size);
return -EACCES;
}
}
if (value_regno >= 0)
/* have read misc data from the stack */
mark_reg_unknown_value(state->regs, value_regno);
return 0;
}
}
/* check read/write into map element returned by bpf_map_lookup_elem() */
static int check_map_access(struct verifier_env *env, u32 regno, int off,
int size)
{
struct bpf_map *map = env->cur_state.regs[regno].map_ptr;
if (off < 0 || off + size > map->value_size) {
verbose("invalid access to map value, value_size=%d off=%d size=%d\n",
map->value_size, off, size);
return -EACCES;
}
return 0;
}
#define MAX_PACKET_OFF 0xffff
static int check_packet_access(struct verifier_env *env, u32 regno, int off,
int size)
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *reg = &regs[regno];
off += reg->off;
if (off < 0 || off + size > reg->range) {
verbose("invalid access to packet, off=%d size=%d, R%d(id=%d,off=%d,r=%d)\n",
off, size, regno, reg->id, reg->off, reg->range);
return -EACCES;
}
return 0;
}
/* check access to 'struct bpf_context' fields */
static int check_ctx_access(struct verifier_env *env, int off, int size,
enum bpf_access_type t)
{
if (env->prog->aux->ops->is_valid_access &&
env->prog->aux->ops->is_valid_access(off, size, t)) {
/* remember the offset of last byte accessed in ctx */
if (env->prog->aux->max_ctx_offset < off + size)
env->prog->aux->max_ctx_offset = off + size;
return 0;
}
verbose("invalid bpf_context access off=%d size=%d\n", off, size);
return -EACCES;
}
static bool is_pointer_value(struct verifier_env *env, int regno)
{
if (env->allow_ptr_leaks)
return false;
switch (env->cur_state.regs[regno].type) {
case UNKNOWN_VALUE:
case CONST_IMM:
return false;
default:
return true;
}
}
static int check_ptr_alignment(struct verifier_env *env, struct reg_state *reg,
int off, int size)
{
if (reg->type != PTR_TO_PACKET) {
if (off % size != 0) {
verbose("misaligned access off %d size %d\n", off, size);
return -EACCES;
} else {
return 0;
}
}
switch (env->prog->type) {
case BPF_PROG_TYPE_SCHED_CLS:
case BPF_PROG_TYPE_SCHED_ACT:
break;
default:
verbose("verifier is misconfigured\n");
return -EACCES;
}
if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
/* misaligned access to packet is ok on x86,arm,arm64 */
return 0;
if (reg->id && size != 1) {
verbose("Unknown packet alignment. Only byte-sized access allowed\n");
return -EACCES;
}
/* skb->data is NET_IP_ALIGN-ed */
if ((NET_IP_ALIGN + reg->off + off) % size != 0) {
verbose("misaligned packet access off %d+%d+%d size %d\n",
NET_IP_ALIGN, reg->off, off, size);
return -EACCES;
}
return 0;
}
/* check whether memory at (regno + off) is accessible for t = (read | write)
* if t==write, value_regno is a register which value is stored into memory
* if t==read, value_regno is a register which will receive the value from memory
* if t==write && value_regno==-1, some unknown value is stored into memory
* if t==read && value_regno==-1, don't care what we read from memory
*/
static int check_mem_access(struct verifier_env *env, u32 regno, int off,
int bpf_size, enum bpf_access_type t,
int value_regno)
{
struct verifier_state *state = &env->cur_state;
struct reg_state *reg = &state->regs[regno];
int size, err = 0;
if (reg->type == PTR_TO_STACK)
off += reg->imm;
size = bpf_size_to_bytes(bpf_size);
if (size < 0)
return size;
err = check_ptr_alignment(env, reg, off, size);
if (err)
return err;
if (reg->type == PTR_TO_MAP_VALUE) {
if (t == BPF_WRITE && value_regno >= 0 &&
is_pointer_value(env, value_regno)) {
verbose("R%d leaks addr into map\n", value_regno);
return -EACCES;
}
err = check_map_access(env, regno, off, size);
if (!err && t == BPF_READ && value_regno >= 0)
mark_reg_unknown_value(state->regs, value_regno);
} else if (reg->type == PTR_TO_CTX) {
if (t == BPF_WRITE && value_regno >= 0 &&
is_pointer_value(env, value_regno)) {
verbose("R%d leaks addr into ctx\n", value_regno);
return -EACCES;
}
err = check_ctx_access(env, off, size, t);
if (!err && t == BPF_READ && value_regno >= 0) {
mark_reg_unknown_value(state->regs, value_regno);
if (off == offsetof(struct __sk_buff, data) &&
env->allow_ptr_leaks)
/* note that reg.[id|off|range] == 0 */
state->regs[value_regno].type = PTR_TO_PACKET;
else if (off == offsetof(struct __sk_buff, data_end) &&
env->allow_ptr_leaks)
state->regs[value_regno].type = PTR_TO_PACKET_END;
}
} else if (reg->type == FRAME_PTR || reg->type == PTR_TO_STACK) {
if (off >= 0 || off < -MAX_BPF_STACK) {
verbose("invalid stack off=%d size=%d\n", off, size);
return -EACCES;
}
if (t == BPF_WRITE) {
if (!env->allow_ptr_leaks &&
state->stack_slot_type[MAX_BPF_STACK + off] == STACK_SPILL &&
size != BPF_REG_SIZE) {
verbose("attempt to corrupt spilled pointer on stack\n");
return -EACCES;
}
err = check_stack_write(state, off, size, value_regno);
} else {
err = check_stack_read(state, off, size, value_regno);
}
} else if (state->regs[regno].type == PTR_TO_PACKET) {
if (t == BPF_WRITE) {
verbose("cannot write into packet\n");
return -EACCES;
}
err = check_packet_access(env, regno, off, size);
if (!err && t == BPF_READ && value_regno >= 0)
mark_reg_unknown_value(state->regs, value_regno);
} else {
verbose("R%d invalid mem access '%s'\n",
regno, reg_type_str[reg->type]);
return -EACCES;
}
if (!err && size <= 2 && value_regno >= 0 && env->allow_ptr_leaks &&
state->regs[value_regno].type == UNKNOWN_VALUE) {
/* 1 or 2 byte load zero-extends, determine the number of
* zero upper bits. Not doing it fo 4 byte load, since
* such values cannot be added to ptr_to_packet anyway.
*/
state->regs[value_regno].imm = 64 - size * 8;
}
return err;
}
static int check_xadd(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
int err;
if ((BPF_SIZE(insn->code) != BPF_W && BPF_SIZE(insn->code) != BPF_DW) ||
insn->imm != 0) {
verbose("BPF_XADD uses reserved fields\n");
return -EINVAL;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
/* check src2 operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
/* check whether atomic_add can read the memory */
err = check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_READ, -1);
if (err)
return err;
/* check whether atomic_add can write into the same memory */
return check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE, -1);
}
/* when register 'regno' is passed into function that will read 'access_size'
* bytes from that pointer, make sure that it's within stack boundary
* and all elements of stack are initialized
*/
static int check_stack_boundary(struct verifier_env *env, int regno,
int access_size, bool zero_size_allowed,
struct bpf_call_arg_meta *meta)
{
struct verifier_state *state = &env->cur_state;
struct reg_state *regs = state->regs;
int off, i;
if (regs[regno].type != PTR_TO_STACK) {
if (zero_size_allowed && access_size == 0 &&
regs[regno].type == CONST_IMM &&
regs[regno].imm == 0)
return 0;
verbose("R%d type=%s expected=%s\n", regno,
reg_type_str[regs[regno].type],
reg_type_str[PTR_TO_STACK]);
return -EACCES;
}
off = regs[regno].imm;
if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
access_size <= 0) {
verbose("invalid stack type R%d off=%d access_size=%d\n",
regno, off, access_size);
return -EACCES;
}
if (meta && meta->raw_mode) {
meta->access_size = access_size;
meta->regno = regno;
return 0;
}
for (i = 0; i < access_size; i++) {
if (state->stack_slot_type[MAX_BPF_STACK + off + i] != STACK_MISC) {
verbose("invalid indirect read from stack off %d+%d size %d\n",
off, i, access_size);
return -EACCES;
}
}
return 0;
}
static int check_func_arg(struct verifier_env *env, u32 regno,
enum bpf_arg_type arg_type,
struct bpf_call_arg_meta *meta)
{
struct reg_state *reg = env->cur_state.regs + regno;
enum bpf_reg_type expected_type;
int err = 0;
if (arg_type == ARG_DONTCARE)
return 0;
if (reg->type == NOT_INIT) {
verbose("R%d !read_ok\n", regno);
return -EACCES;
}
if (arg_type == ARG_ANYTHING) {
if (is_pointer_value(env, regno)) {
verbose("R%d leaks addr into helper function\n", regno);
return -EACCES;
}
return 0;
}
if (arg_type == ARG_PTR_TO_MAP_KEY ||
arg_type == ARG_PTR_TO_MAP_VALUE) {
expected_type = PTR_TO_STACK;
} else if (arg_type == ARG_CONST_STACK_SIZE ||
arg_type == ARG_CONST_STACK_SIZE_OR_ZERO) {
expected_type = CONST_IMM;
} else if (arg_type == ARG_CONST_MAP_PTR) {
expected_type = CONST_PTR_TO_MAP;
} else if (arg_type == ARG_PTR_TO_CTX) {
expected_type = PTR_TO_CTX;
} else if (arg_type == ARG_PTR_TO_STACK ||
arg_type == ARG_PTR_TO_RAW_STACK) {
expected_type = PTR_TO_STACK;
/* One exception here. In case function allows for NULL to be
* passed in as argument, it's a CONST_IMM type. Final test
* happens during stack boundary checking.
*/
if (reg->type == CONST_IMM && reg->imm == 0)
expected_type = CONST_IMM;
meta->raw_mode = arg_type == ARG_PTR_TO_RAW_STACK;
} else {
verbose("unsupported arg_type %d\n", arg_type);
return -EFAULT;
}
if (reg->type != expected_type) {
verbose("R%d type=%s expected=%s\n", regno,
reg_type_str[reg->type], reg_type_str[expected_type]);
return -EACCES;
}
if (arg_type == ARG_CONST_MAP_PTR) {
/* bpf_map_xxx(map_ptr) call: remember that map_ptr */
meta->map_ptr = reg->map_ptr;
} else if (arg_type == ARG_PTR_TO_MAP_KEY) {
/* bpf_map_xxx(..., map_ptr, ..., key) call:
* check that [key, key + map->key_size) are within
* stack limits and initialized
*/
if (!meta->map_ptr) {
/* in function declaration map_ptr must come before
* map_key, so that it's verified and known before
* we have to check map_key here. Otherwise it means
* that kernel subsystem misconfigured verifier
*/
verbose("invalid map_ptr to access map->key\n");
return -EACCES;
}
err = check_stack_boundary(env, regno, meta->map_ptr->key_size,
false, NULL);
} else if (arg_type == ARG_PTR_TO_MAP_VALUE) {
/* bpf_map_xxx(..., map_ptr, ..., value) call:
* check [value, value + map->value_size) validity
*/
if (!meta->map_ptr) {
/* kernel subsystem misconfigured verifier */
verbose("invalid map_ptr to access map->value\n");
return -EACCES;
}
err = check_stack_boundary(env, regno,
meta->map_ptr->value_size,
false, NULL);
} else if (arg_type == ARG_CONST_STACK_SIZE ||
arg_type == ARG_CONST_STACK_SIZE_OR_ZERO) {
bool zero_size_allowed = (arg_type == ARG_CONST_STACK_SIZE_OR_ZERO);
/* bpf_xxx(..., buf, len) call will access 'len' bytes
* from stack pointer 'buf'. Check it
* note: regno == len, regno - 1 == buf
*/
if (regno == 0) {
/* kernel subsystem misconfigured verifier */
verbose("ARG_CONST_STACK_SIZE cannot be first argument\n");
return -EACCES;
}
err = check_stack_boundary(env, regno - 1, reg->imm,
zero_size_allowed, meta);
}
return err;
}
static int check_map_func_compatibility(struct bpf_map *map, int func_id)
{
if (!map)
return 0;
/* We need a two way check, first is from map perspective ... */
switch (map->map_type) {
case BPF_MAP_TYPE_PROG_ARRAY:
if (func_id != BPF_FUNC_tail_call)
goto error;
break;
case BPF_MAP_TYPE_PERF_EVENT_ARRAY:
if (func_id != BPF_FUNC_perf_event_read &&
func_id != BPF_FUNC_perf_event_output)
goto error;
break;
case BPF_MAP_TYPE_STACK_TRACE:
if (func_id != BPF_FUNC_get_stackid)
goto error;
break;
default:
break;
}
/* ... and second from the function itself. */
switch (func_id) {
case BPF_FUNC_tail_call:
if (map->map_type != BPF_MAP_TYPE_PROG_ARRAY)
goto error;
break;
case BPF_FUNC_perf_event_read:
case BPF_FUNC_perf_event_output:
if (map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
goto error;
break;
case BPF_FUNC_get_stackid:
if (map->map_type != BPF_MAP_TYPE_STACK_TRACE)
goto error;
break;
default:
break;
}
return 0;
error:
verbose("cannot pass map_type %d into func %d\n",
map->map_type, func_id);
return -EINVAL;
}
static int check_raw_mode(const struct bpf_func_proto *fn)
{
int count = 0;
if (fn->arg1_type == ARG_PTR_TO_RAW_STACK)
count++;
if (fn->arg2_type == ARG_PTR_TO_RAW_STACK)
count++;
if (fn->arg3_type == ARG_PTR_TO_RAW_STACK)
count++;
if (fn->arg4_type == ARG_PTR_TO_RAW_STACK)
count++;
if (fn->arg5_type == ARG_PTR_TO_RAW_STACK)
count++;
return count > 1 ? -EINVAL : 0;
}
static void clear_all_pkt_pointers(struct verifier_env *env)
{
struct verifier_state *state = &env->cur_state;
struct reg_state *regs = state->regs, *reg;
int i;
for (i = 0; i < MAX_BPF_REG; i++)
if (regs[i].type == PTR_TO_PACKET ||
regs[i].type == PTR_TO_PACKET_END)
mark_reg_unknown_value(regs, i);
for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
if (state->stack_slot_type[i] != STACK_SPILL)
continue;
reg = &state->spilled_regs[i / BPF_REG_SIZE];
if (reg->type != PTR_TO_PACKET &&
reg->type != PTR_TO_PACKET_END)
continue;
reg->type = UNKNOWN_VALUE;
reg->imm = 0;
}
}
static int check_call(struct verifier_env *env, int func_id)
{
struct verifier_state *state = &env->cur_state;
const struct bpf_func_proto *fn = NULL;
struct reg_state *regs = state->regs;
struct reg_state *reg;
struct bpf_call_arg_meta meta;
bool changes_data;
int i, err;
/* find function prototype */
if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID) {
verbose("invalid func %d\n", func_id);
return -EINVAL;
}
if (env->prog->aux->ops->get_func_proto)
fn = env->prog->aux->ops->get_func_proto(func_id);
if (!fn) {
verbose("unknown func %d\n", func_id);
return -EINVAL;
}
/* eBPF programs must be GPL compatible to use GPL-ed functions */
if (!env->prog->gpl_compatible && fn->gpl_only) {
verbose("cannot call GPL only function from proprietary program\n");
return -EINVAL;
}
changes_data = bpf_helper_changes_skb_data(fn->func);
memset(&meta, 0, sizeof(meta));
/* We only support one arg being in raw mode at the moment, which
* is sufficient for the helper functions we have right now.
*/
err = check_raw_mode(fn);
if (err) {
verbose("kernel subsystem misconfigured func %d\n", func_id);
return err;
}
/* check args */
err = check_func_arg(env, BPF_REG_1, fn->arg1_type, &meta);
if (err)
return err;
err = check_func_arg(env, BPF_REG_2, fn->arg2_type, &meta);
if (err)
return err;
err = check_func_arg(env, BPF_REG_3, fn->arg3_type, &meta);
if (err)
return err;
err = check_func_arg(env, BPF_REG_4, fn->arg4_type, &meta);
if (err)
return err;
err = check_func_arg(env, BPF_REG_5, fn->arg5_type, &meta);
if (err)
return err;
/* Mark slots with STACK_MISC in case of raw mode, stack offset
* is inferred from register state.
*/
for (i = 0; i < meta.access_size; i++) {
err = check_mem_access(env, meta.regno, i, BPF_B, BPF_WRITE, -1);
if (err)
return err;
}
/* reset caller saved regs */
for (i = 0; i < CALLER_SAVED_REGS; i++) {
reg = regs + caller_saved[i];
reg->type = NOT_INIT;
reg->imm = 0;
}
/* update return register */
if (fn->ret_type == RET_INTEGER) {
regs[BPF_REG_0].type = UNKNOWN_VALUE;
} else if (fn->ret_type == RET_VOID) {
regs[BPF_REG_0].type = NOT_INIT;
} else if (fn->ret_type == RET_PTR_TO_MAP_VALUE_OR_NULL) {
regs[BPF_REG_0].type = PTR_TO_MAP_VALUE_OR_NULL;
/* remember map_ptr, so that check_map_access()
* can check 'value_size' boundary of memory access
* to map element returned from bpf_map_lookup_elem()
*/
if (meta.map_ptr == NULL) {
verbose("kernel subsystem misconfigured verifier\n");
return -EINVAL;
}
regs[BPF_REG_0].map_ptr = meta.map_ptr;
} else {
verbose("unknown return type %d of func %d\n",
fn->ret_type, func_id);
return -EINVAL;
}
err = check_map_func_compatibility(meta.map_ptr, func_id);
if (err)
return err;
if (changes_data)
clear_all_pkt_pointers(env);
return 0;
}
static int check_packet_ptr_add(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *dst_reg = &regs[insn->dst_reg];
struct reg_state *src_reg = &regs[insn->src_reg];
struct reg_state tmp_reg;
s32 imm;
if (BPF_SRC(insn->code) == BPF_K) {
/* pkt_ptr += imm */
imm = insn->imm;
add_imm:
if (imm <= 0) {
verbose("addition of negative constant to packet pointer is not allowed\n");
return -EACCES;
}
if (imm >= MAX_PACKET_OFF ||
imm + dst_reg->off >= MAX_PACKET_OFF) {
verbose("constant %d is too large to add to packet pointer\n",
imm);
return -EACCES;
}
/* a constant was added to pkt_ptr.
* Remember it while keeping the same 'id'
*/
dst_reg->off += imm;
} else {
if (src_reg->type == PTR_TO_PACKET) {
/* R6=pkt(id=0,off=0,r=62) R7=imm22; r7 += r6 */
tmp_reg = *dst_reg; /* save r7 state */
*dst_reg = *src_reg; /* copy pkt_ptr state r6 into r7 */
src_reg = &tmp_reg; /* pretend it's src_reg state */
/* if the checks below reject it, the copy won't matter,
* since we're rejecting the whole program. If all ok,
* then imm22 state will be added to r7
* and r7 will be pkt(id=0,off=22,r=62) while
* r6 will stay as pkt(id=0,off=0,r=62)
*/
}
if (src_reg->type == CONST_IMM) {
/* pkt_ptr += reg where reg is known constant */
imm = src_reg->imm;
goto add_imm;
}
/* disallow pkt_ptr += reg
* if reg is not uknown_value with guaranteed zero upper bits
* otherwise pkt_ptr may overflow and addition will become
* subtraction which is not allowed
*/
if (src_reg->type != UNKNOWN_VALUE) {
verbose("cannot add '%s' to ptr_to_packet\n",
reg_type_str[src_reg->type]);
return -EACCES;
}
if (src_reg->imm < 48) {
verbose("cannot add integer value with %lld upper zero bits to ptr_to_packet\n",
src_reg->imm);
return -EACCES;
}
/* dst_reg stays as pkt_ptr type and since some positive
* integer value was added to the pointer, increment its 'id'
*/
dst_reg->id++;
/* something was added to pkt_ptr, set range and off to zero */
dst_reg->off = 0;
dst_reg->range = 0;
}
return 0;
}
static int evaluate_reg_alu(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *dst_reg = &regs[insn->dst_reg];
u8 opcode = BPF_OP(insn->code);
s64 imm_log2;
/* for type == UNKNOWN_VALUE:
* imm > 0 -> number of zero upper bits
* imm == 0 -> don't track which is the same as all bits can be non-zero
*/
if (BPF_SRC(insn->code) == BPF_X) {
struct reg_state *src_reg = &regs[insn->src_reg];
if (src_reg->type == UNKNOWN_VALUE && src_reg->imm > 0 &&
dst_reg->imm && opcode == BPF_ADD) {
/* dreg += sreg
* where both have zero upper bits. Adding them
* can only result making one more bit non-zero
* in the larger value.
* Ex. 0xffff (imm=48) + 1 (imm=63) = 0x10000 (imm=47)
* 0xffff (imm=48) + 0xffff = 0x1fffe (imm=47)
*/
dst_reg->imm = min(dst_reg->imm, src_reg->imm);
dst_reg->imm--;
return 0;
}
if (src_reg->type == CONST_IMM && src_reg->imm > 0 &&
dst_reg->imm && opcode == BPF_ADD) {
/* dreg += sreg
* where dreg has zero upper bits and sreg is const.
* Adding them can only result making one more bit
* non-zero in the larger value.
*/
imm_log2 = __ilog2_u64((long long)src_reg->imm);
dst_reg->imm = min(dst_reg->imm, 63 - imm_log2);
dst_reg->imm--;
return 0;
}
/* all other cases non supported yet, just mark dst_reg */
dst_reg->imm = 0;
return 0;
}
/* sign extend 32-bit imm into 64-bit to make sure that
* negative values occupy bit 63. Note ilog2() would have
* been incorrect, since sizeof(insn->imm) == 4
*/
imm_log2 = __ilog2_u64((long long)insn->imm);
if (dst_reg->imm && opcode == BPF_LSH) {
/* reg <<= imm
* if reg was a result of 2 byte load, then its imm == 48
* which means that upper 48 bits are zero and shifting this reg
* left by 4 would mean that upper 44 bits are still zero
*/
dst_reg->imm -= insn->imm;
} else if (dst_reg->imm && opcode == BPF_MUL) {
/* reg *= imm
* if multiplying by 14 subtract 4
* This is conservative calculation of upper zero bits.
* It's not trying to special case insn->imm == 1 or 0 cases
*/
dst_reg->imm -= imm_log2 + 1;
} else if (opcode == BPF_AND) {
/* reg &= imm */
dst_reg->imm = 63 - imm_log2;
} else if (dst_reg->imm && opcode == BPF_ADD) {
/* reg += imm */
dst_reg->imm = min(dst_reg->imm, 63 - imm_log2);
dst_reg->imm--;
} else if (opcode == BPF_RSH) {
/* reg >>= imm
* which means that after right shift, upper bits will be zero
* note that verifier already checked that
* 0 <= imm < 64 for shift insn
*/
dst_reg->imm += insn->imm;
if (unlikely(dst_reg->imm > 64))
/* some dumb code did:
* r2 = *(u32 *)mem;
* r2 >>= 32;
* and all bits are zero now */
dst_reg->imm = 64;
} else {
/* all other alu ops, means that we don't know what will
* happen to the value, mark it with unknown number of zero bits
*/
dst_reg->imm = 0;
}
if (dst_reg->imm < 0) {
/* all 64 bits of the register can contain non-zero bits
* and such value cannot be added to ptr_to_packet, since it
* may overflow, mark it as unknown to avoid further eval
*/
dst_reg->imm = 0;
}
return 0;
}
static int evaluate_reg_imm_alu(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *dst_reg = &regs[insn->dst_reg];
struct reg_state *src_reg = &regs[insn->src_reg];
u8 opcode = BPF_OP(insn->code);
/* dst_reg->type == CONST_IMM here, simulate execution of 'add' insn.
* Don't care about overflow or negative values, just add them
*/
if (opcode == BPF_ADD && BPF_SRC(insn->code) == BPF_K)
dst_reg->imm += insn->imm;
else if (opcode == BPF_ADD && BPF_SRC(insn->code) == BPF_X &&
src_reg->type == CONST_IMM)
dst_reg->imm += src_reg->imm;
else
mark_reg_unknown_value(regs, insn->dst_reg);
return 0;
}
/* check validity of 32-bit and 64-bit arithmetic operations */
static int check_alu_op(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs, *dst_reg;
u8 opcode = BPF_OP(insn->code);
int err;
if (opcode == BPF_END || opcode == BPF_NEG) {
if (opcode == BPF_NEG) {
if (BPF_SRC(insn->code) != 0 ||
insn->src_reg != BPF_REG_0 ||
insn->off != 0 || insn->imm != 0) {
verbose("BPF_NEG uses reserved fields\n");
return -EINVAL;
}
} else {
if (insn->src_reg != BPF_REG_0 || insn->off != 0 ||
(insn->imm != 16 && insn->imm != 32 && insn->imm != 64)) {
verbose("BPF_END uses reserved fields\n");
return -EINVAL;
}
}
/* check src operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer arithmetic prohibited\n",
insn->dst_reg);
return -EACCES;
}
/* check dest operand */
err = check_reg_arg(regs, insn->dst_reg, DST_OP);
if (err)
return err;
} else if (opcode == BPF_MOV) {
if (BPF_SRC(insn->code) == BPF_X) {
if (insn->imm != 0 || insn->off != 0) {
verbose("BPF_MOV uses reserved fields\n");
return -EINVAL;
}
/* check src operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
} else {
if (insn->src_reg != BPF_REG_0 || insn->off != 0) {
verbose("BPF_MOV uses reserved fields\n");
return -EINVAL;
}
}
/* check dest operand */
err = check_reg_arg(regs, insn->dst_reg, DST_OP);
if (err)
return err;
if (BPF_SRC(insn->code) == BPF_X) {
if (BPF_CLASS(insn->code) == BPF_ALU64) {
/* case: R1 = R2
* copy register state to dest reg
*/
regs[insn->dst_reg] = regs[insn->src_reg];
} else {
if (is_pointer_value(env, insn->src_reg)) {
verbose("R%d partial copy of pointer\n",
insn->src_reg);
return -EACCES;
}
regs[insn->dst_reg].type = UNKNOWN_VALUE;
regs[insn->dst_reg].map_ptr = NULL;
}
} else {
/* case: R = imm
* remember the value we stored into this reg
*/
regs[insn->dst_reg].type = CONST_IMM;
regs[insn->dst_reg].imm = insn->imm;
}
} else if (opcode > BPF_END) {
verbose("invalid BPF_ALU opcode %x\n", opcode);
return -EINVAL;
} else { /* all other ALU ops: and, sub, xor, add, ... */
if (BPF_SRC(insn->code) == BPF_X) {
if (insn->imm != 0 || insn->off != 0) {
verbose("BPF_ALU uses reserved fields\n");
return -EINVAL;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
} else {
if (insn->src_reg != BPF_REG_0 || insn->off != 0) {
verbose("BPF_ALU uses reserved fields\n");
return -EINVAL;
}
}
/* check src2 operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
if ((opcode == BPF_MOD || opcode == BPF_DIV) &&
BPF_SRC(insn->code) == BPF_K && insn->imm == 0) {
verbose("div by zero\n");
return -EINVAL;
}
if ((opcode == BPF_LSH || opcode == BPF_RSH ||
opcode == BPF_ARSH) && BPF_SRC(insn->code) == BPF_K) {
int size = BPF_CLASS(insn->code) == BPF_ALU64 ? 64 : 32;
if (insn->imm < 0 || insn->imm >= size) {
verbose("invalid shift %d\n", insn->imm);
return -EINVAL;
}
}
/* check dest operand */
err = check_reg_arg(regs, insn->dst_reg, DST_OP_NO_MARK);
if (err)
return err;
dst_reg = &regs[insn->dst_reg];
/* pattern match 'bpf_add Rx, imm' instruction */
if (opcode == BPF_ADD && BPF_CLASS(insn->code) == BPF_ALU64 &&
dst_reg->type == FRAME_PTR && BPF_SRC(insn->code) == BPF_K) {
dst_reg->type = PTR_TO_STACK;
dst_reg->imm = insn->imm;
return 0;
} else if (opcode == BPF_ADD &&
BPF_CLASS(insn->code) == BPF_ALU64 &&
(dst_reg->type == PTR_TO_PACKET ||
(BPF_SRC(insn->code) == BPF_X &&
regs[insn->src_reg].type == PTR_TO_PACKET))) {
/* ptr_to_packet += K|X */
return check_packet_ptr_add(env, insn);
} else if (BPF_CLASS(insn->code) == BPF_ALU64 &&
dst_reg->type == UNKNOWN_VALUE &&
env->allow_ptr_leaks) {
/* unknown += K|X */
return evaluate_reg_alu(env, insn);
} else if (BPF_CLASS(insn->code) == BPF_ALU64 &&
dst_reg->type == CONST_IMM &&
env->allow_ptr_leaks) {
/* reg_imm += K|X */
return evaluate_reg_imm_alu(env, insn);
} else if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer arithmetic prohibited\n",
insn->dst_reg);
return -EACCES;
} else if (BPF_SRC(insn->code) == BPF_X &&
is_pointer_value(env, insn->src_reg)) {
verbose("R%d pointer arithmetic prohibited\n",
insn->src_reg);
return -EACCES;
}
/* mark dest operand */
mark_reg_unknown_value(regs, insn->dst_reg);
}
return 0;
}
static void find_good_pkt_pointers(struct verifier_env *env,
struct reg_state *dst_reg)
{
struct verifier_state *state = &env->cur_state;
struct reg_state *regs = state->regs, *reg;
int i;
/* r2 = r3;
* r2 += 8
* if (r2 > pkt_end) goto somewhere
* r2 == dst_reg, pkt_end == src_reg,
* r2=pkt(id=n,off=8,r=0)
* r3=pkt(id=n,off=0,r=0)
* find register r3 and mark its range as r3=pkt(id=n,off=0,r=8)
* so that range of bytes [r3, r3 + 8) is safe to access
*/
for (i = 0; i < MAX_BPF_REG; i++)
if (regs[i].type == PTR_TO_PACKET && regs[i].id == dst_reg->id)
regs[i].range = dst_reg->off;
for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
if (state->stack_slot_type[i] != STACK_SPILL)
continue;
reg = &state->spilled_regs[i / BPF_REG_SIZE];
if (reg->type == PTR_TO_PACKET && reg->id == dst_reg->id)
reg->range = dst_reg->off;
}
}
static int check_cond_jmp_op(struct verifier_env *env,
struct bpf_insn *insn, int *insn_idx)
{
struct reg_state *regs = env->cur_state.regs, *dst_reg;
struct verifier_state *other_branch;
u8 opcode = BPF_OP(insn->code);
int err;
if (opcode > BPF_EXIT) {
verbose("invalid BPF_JMP opcode %x\n", opcode);
return -EINVAL;
}
if (BPF_SRC(insn->code) == BPF_X) {
if (insn->imm != 0) {
verbose("BPF_JMP uses reserved fields\n");
return -EINVAL;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
if (is_pointer_value(env, insn->src_reg)) {
verbose("R%d pointer comparison prohibited\n",
insn->src_reg);
return -EACCES;
}
} else {
if (insn->src_reg != BPF_REG_0) {
verbose("BPF_JMP uses reserved fields\n");
return -EINVAL;
}
}
/* check src2 operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
dst_reg = &regs[insn->dst_reg];
/* detect if R == 0 where R was initialized to zero earlier */
if (BPF_SRC(insn->code) == BPF_K &&
(opcode == BPF_JEQ || opcode == BPF_JNE) &&
dst_reg->type == CONST_IMM && dst_reg->imm == insn->imm) {
if (opcode == BPF_JEQ) {
/* if (imm == imm) goto pc+off;
* only follow the goto, ignore fall-through
*/
*insn_idx += insn->off;
return 0;
} else {
/* if (imm != imm) goto pc+off;
* only follow fall-through branch, since
* that's where the program will go
*/
return 0;
}
}
other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx);
if (!other_branch)
return -EFAULT;
/* detect if R == 0 where R is returned value from bpf_map_lookup_elem() */
if (BPF_SRC(insn->code) == BPF_K &&
insn->imm == 0 && (opcode == BPF_JEQ || opcode == BPF_JNE) &&
dst_reg->type == PTR_TO_MAP_VALUE_OR_NULL) {
if (opcode == BPF_JEQ) {
/* next fallthrough insn can access memory via
* this register
*/
regs[insn->dst_reg].type = PTR_TO_MAP_VALUE;
/* branch targer cannot access it, since reg == 0 */
mark_reg_unknown_value(other_branch->regs,
insn->dst_reg);
} else {
other_branch->regs[insn->dst_reg].type = PTR_TO_MAP_VALUE;
mark_reg_unknown_value(regs, insn->dst_reg);
}
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGT &&
dst_reg->type == PTR_TO_PACKET &&
regs[insn->src_reg].type == PTR_TO_PACKET_END) {
find_good_pkt_pointers(env, dst_reg);
} else if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer comparison prohibited\n", insn->dst_reg);
return -EACCES;
}
if (log_level)
print_verifier_state(&env->cur_state);
return 0;
}
/* return the map pointer stored inside BPF_LD_IMM64 instruction */
static struct bpf_map *ld_imm64_to_map_ptr(struct bpf_insn *insn)
{
u64 imm64 = ((u64) (u32) insn[0].imm) | ((u64) (u32) insn[1].imm) << 32;
return (struct bpf_map *) (unsigned long) imm64;
}
/* verify BPF_LD_IMM64 instruction */
static int check_ld_imm(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
int err;
if (BPF_SIZE(insn->code) != BPF_DW) {
verbose("invalid BPF_LD_IMM insn\n");
return -EINVAL;
}
if (insn->off != 0) {
verbose("BPF_LD_IMM64 uses reserved fields\n");
return -EINVAL;
}
err = check_reg_arg(regs, insn->dst_reg, DST_OP);
if (err)
return err;
if (insn->src_reg == 0)
/* generic move 64-bit immediate into a register */
return 0;
/* replace_map_fd_with_map_ptr() should have caught bad ld_imm64 */
BUG_ON(insn->src_reg != BPF_PSEUDO_MAP_FD);
regs[insn->dst_reg].type = CONST_PTR_TO_MAP;
regs[insn->dst_reg].map_ptr = ld_imm64_to_map_ptr(insn);
return 0;
}
static bool may_access_skb(enum bpf_prog_type type)
{
switch (type) {
case BPF_PROG_TYPE_SOCKET_FILTER:
case BPF_PROG_TYPE_SCHED_CLS:
case BPF_PROG_TYPE_SCHED_ACT:
return true;
default:
return false;
}
}
/* verify safety of LD_ABS|LD_IND instructions:
* - they can only appear in the programs where ctx == skb
* - since they are wrappers of function calls, they scratch R1-R5 registers,
* preserve R6-R9, and store return value into R0
*
* Implicit input:
* ctx == skb == R6 == CTX
*
* Explicit input:
* SRC == any register
* IMM == 32-bit immediate
*
* Output:
* R0 - 8/16/32-bit skb data converted to cpu endianness
*/
static int check_ld_abs(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
u8 mode = BPF_MODE(insn->code);
struct reg_state *reg;
int i, err;
if (!may_access_skb(env->prog->type)) {
verbose("BPF_LD_[ABS|IND] instructions not allowed for this program type\n");
return -EINVAL;
}
if (insn->dst_reg != BPF_REG_0 || insn->off != 0 ||
BPF_SIZE(insn->code) == BPF_DW ||
(mode == BPF_ABS && insn->src_reg != BPF_REG_0)) {
verbose("BPF_LD_[ABS|IND] uses reserved fields\n");
return -EINVAL;
}
/* check whether implicit source operand (register R6) is readable */
err = check_reg_arg(regs, BPF_REG_6, SRC_OP);
if (err)
return err;
if (regs[BPF_REG_6].type != PTR_TO_CTX) {
verbose("at the time of BPF_LD_ABS|IND R6 != pointer to skb\n");
return -EINVAL;
}
if (mode == BPF_IND) {
/* check explicit source operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
}
/* reset caller saved regs to unreadable */
for (i = 0; i < CALLER_SAVED_REGS; i++) {
reg = regs + caller_saved[i];
reg->type = NOT_INIT;
reg->imm = 0;
}
/* mark destination R0 register as readable, since it contains
* the value fetched from the packet
*/
regs[BPF_REG_0].type = UNKNOWN_VALUE;
return 0;
}
/* non-recursive DFS pseudo code
* 1 procedure DFS-iterative(G,v):
* 2 label v as discovered
* 3 let S be a stack
* 4 S.push(v)
* 5 while S is not empty
* 6 t <- S.pop()
* 7 if t is what we're looking for:
* 8 return t
* 9 for all edges e in G.adjacentEdges(t) do
* 10 if edge e is already labelled
* 11 continue with the next edge
* 12 w <- G.adjacentVertex(t,e)
* 13 if vertex w is not discovered and not explored
* 14 label e as tree-edge
* 15 label w as discovered
* 16 S.push(w)
* 17 continue at 5
* 18 else if vertex w is discovered
* 19 label e as back-edge
* 20 else
* 21 // vertex w is explored
* 22 label e as forward- or cross-edge
* 23 label t as explored
* 24 S.pop()
*
* convention:
* 0x10 - discovered
* 0x11 - discovered and fall-through edge labelled
* 0x12 - discovered and fall-through and branch edges labelled
* 0x20 - explored
*/
enum {
DISCOVERED = 0x10,
EXPLORED = 0x20,
FALLTHROUGH = 1,
BRANCH = 2,
};
#define STATE_LIST_MARK ((struct verifier_state_list *) -1L)
static int *insn_stack; /* stack of insns to process */
static int cur_stack; /* current stack index */
static int *insn_state;
/* t, w, e - match pseudo-code above:
* t - index of current instruction
* w - next instruction
* e - edge
*/
static int push_insn(int t, int w, int e, struct verifier_env *env)
{
if (e == FALLTHROUGH && insn_state[t] >= (DISCOVERED | FALLTHROUGH))
return 0;
if (e == BRANCH && insn_state[t] >= (DISCOVERED | BRANCH))
return 0;
if (w < 0 || w >= env->prog->len) {
verbose("jump out of range from insn %d to %d\n", t, w);
return -EINVAL;
}
if (e == BRANCH)
/* mark branch target for state pruning */
env->explored_states[w] = STATE_LIST_MARK;
if (insn_state[w] == 0) {
/* tree-edge */
insn_state[t] = DISCOVERED | e;
insn_state[w] = DISCOVERED;
if (cur_stack >= env->prog->len)
return -E2BIG;
insn_stack[cur_stack++] = w;
return 1;
} else if ((insn_state[w] & 0xF0) == DISCOVERED) {
verbose("back-edge from insn %d to %d\n", t, w);
return -EINVAL;
} else if (insn_state[w] == EXPLORED) {
/* forward- or cross-edge */
insn_state[t] = DISCOVERED | e;
} else {
verbose("insn state internal bug\n");
return -EFAULT;
}
return 0;
}
/* non-recursive depth-first-search to detect loops in BPF program
* loop == back-edge in directed graph
*/
static int check_cfg(struct verifier_env *env)
{
struct bpf_insn *insns = env->prog->insnsi;
int insn_cnt = env->prog->len;
int ret = 0;
int i, t;
insn_state = kcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
if (!insn_state)
return -ENOMEM;
insn_stack = kcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
if (!insn_stack) {
kfree(insn_state);
return -ENOMEM;
}
insn_state[0] = DISCOVERED; /* mark 1st insn as discovered */
insn_stack[0] = 0; /* 0 is the first instruction */
cur_stack = 1;
peek_stack:
if (cur_stack == 0)
goto check_state;
t = insn_stack[cur_stack - 1];
if (BPF_CLASS(insns[t].code) == BPF_JMP) {
u8 opcode = BPF_OP(insns[t].code);
if (opcode == BPF_EXIT) {
goto mark_explored;
} else if (opcode == BPF_CALL) {
ret = push_insn(t, t + 1, FALLTHROUGH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
if (t + 1 < insn_cnt)
env->explored_states[t + 1] = STATE_LIST_MARK;
} else if (opcode == BPF_JA) {
if (BPF_SRC(insns[t].code) != BPF_K) {
ret = -EINVAL;
goto err_free;
}
/* unconditional jump with single edge */
ret = push_insn(t, t + insns[t].off + 1,
FALLTHROUGH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
/* tell verifier to check for equivalent states
* after every call and jump
*/
if (t + 1 < insn_cnt)
env->explored_states[t + 1] = STATE_LIST_MARK;
} else {
/* conditional jump with two edges */
ret = push_insn(t, t + 1, FALLTHROUGH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
ret = push_insn(t, t + insns[t].off + 1, BRANCH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
}
} else {
/* all other non-branch instructions with single
* fall-through edge
*/
ret = push_insn(t, t + 1, FALLTHROUGH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
}
mark_explored:
insn_state[t] = EXPLORED;
if (cur_stack-- <= 0) {
verbose("pop stack internal bug\n");
ret = -EFAULT;
goto err_free;
}
goto peek_stack;
check_state:
for (i = 0; i < insn_cnt; i++) {
if (insn_state[i] != EXPLORED) {
verbose("unreachable insn %d\n", i);
ret = -EINVAL;
goto err_free;
}
}
ret = 0; /* cfg looks good */
err_free:
kfree(insn_state);
kfree(insn_stack);
return ret;
}
/* the following conditions reduce the number of explored insns
* from ~140k to ~80k for ultra large programs that use a lot of ptr_to_packet
*/
static bool compare_ptrs_to_packet(struct reg_state *old, struct reg_state *cur)
{
if (old->id != cur->id)
return false;
/* old ptr_to_packet is more conservative, since it allows smaller
* range. Ex:
* old(off=0,r=10) is equal to cur(off=0,r=20), because
* old(off=0,r=10) means that with range=10 the verifier proceeded
* further and found no issues with the program. Now we're in the same
* spot with cur(off=0,r=20), so we're safe too, since anything further
* will only be looking at most 10 bytes after this pointer.
*/
if (old->off == cur->off && old->range < cur->range)
return true;
/* old(off=20,r=10) is equal to cur(off=22,re=22 or 5 or 0)
* since both cannot be used for packet access and safe(old)
* pointer has smaller off that could be used for further
* 'if (ptr > data_end)' check
* Ex:
* old(off=20,r=10) and cur(off=22,r=22) and cur(off=22,r=0) mean
* that we cannot access the packet.
* The safe range is:
* [ptr, ptr + range - off)
* so whenever off >=range, it means no safe bytes from this pointer.
* When comparing old->off <= cur->off, it means that older code
* went with smaller offset and that offset was later
* used to figure out the safe range after 'if (ptr > data_end)' check
* Say, 'old' state was explored like:
* ... R3(off=0, r=0)
* R4 = R3 + 20
* ... now R4(off=20,r=0) <-- here
* if (R4 > data_end)
* ... R4(off=20,r=20), R3(off=0,r=20) and R3 can be used to access.
* ... the code further went all the way to bpf_exit.
* Now the 'cur' state at the mark 'here' has R4(off=30,r=0).
* old_R4(off=20,r=0) equal to cur_R4(off=30,r=0), since if the verifier
* goes further, such cur_R4 will give larger safe packet range after
* 'if (R4 > data_end)' and all further insn were already good with r=20,
* so they will be good with r=30 and we can prune the search.
*/
if (old->off <= cur->off &&
old->off >= old->range && cur->off >= cur->range)
return true;
return false;
}
/* compare two verifier states
*
* all states stored in state_list are known to be valid, since
* verifier reached 'bpf_exit' instruction through them
*
* this function is called when verifier exploring different branches of
* execution popped from the state stack. If it sees an old state that has
* more strict register state and more strict stack state then this execution
* branch doesn't need to be explored further, since verifier already
* concluded that more strict state leads to valid finish.
*
* Therefore two states are equivalent if register state is more conservative
* and explored stack state is more conservative than the current one.
* Example:
* explored current
* (slot1=INV slot2=MISC) == (slot1=MISC slot2=MISC)
* (slot1=MISC slot2=MISC) != (slot1=INV slot2=MISC)
*
* In other words if current stack state (one being explored) has more
* valid slots than old one that already passed validation, it means
* the verifier can stop exploring and conclude that current state is valid too
*
* Similarly with registers. If explored state has register type as invalid
* whereas register type in current state is meaningful, it means that
* the current state will reach 'bpf_exit' instruction safely
*/
static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
{
struct reg_state *rold, *rcur;
int i;
for (i = 0; i < MAX_BPF_REG; i++) {
rold = &old->regs[i];
rcur = &cur->regs[i];
if (memcmp(rold, rcur, sizeof(*rold)) == 0)
continue;
if (rold->type == NOT_INIT ||
(rold->type == UNKNOWN_VALUE && rcur->type != NOT_INIT))
continue;
if (rold->type == PTR_TO_PACKET && rcur->type == PTR_TO_PACKET &&
compare_ptrs_to_packet(rold, rcur))
continue;
return false;
}
for (i = 0; i < MAX_BPF_STACK; i++) {
if (old->stack_slot_type[i] == STACK_INVALID)
continue;
if (old->stack_slot_type[i] != cur->stack_slot_type[i])
/* Ex: old explored (safe) state has STACK_SPILL in
* this stack slot, but current has has STACK_MISC ->
* this verifier states are not equivalent,
* return false to continue verification of this path
*/
return false;
if (i % BPF_REG_SIZE)
continue;
if (memcmp(&old->spilled_regs[i / BPF_REG_SIZE],
&cur->spilled_regs[i / BPF_REG_SIZE],
sizeof(old->spilled_regs[0])))
/* when explored and current stack slot types are
* the same, check that stored pointers types
* are the same as well.
* Ex: explored safe path could have stored
* (struct reg_state) {.type = PTR_TO_STACK, .imm = -8}
* but current path has stored:
* (struct reg_state) {.type = PTR_TO_STACK, .imm = -16}
* such verifier states are not equivalent.
* return false to continue verification of this path
*/
return false;
else
continue;
}
return true;
}
static int is_state_visited(struct verifier_env *env, int insn_idx)
{
struct verifier_state_list *new_sl;
struct verifier_state_list *sl;
sl = env->explored_states[insn_idx];
if (!sl)
/* this 'insn_idx' instruction wasn't marked, so we will not
* be doing state search here
*/
return 0;
while (sl != STATE_LIST_MARK) {
if (states_equal(&sl->state, &env->cur_state))
/* reached equivalent register/stack state,
* prune the search
*/
return 1;
sl = sl->next;
}
/* there were no equivalent states, remember current one.
* technically the current state is not proven to be safe yet,
* but it will either reach bpf_exit (which means it's safe) or
* it will be rejected. Since there are no loops, we won't be
* seeing this 'insn_idx' instruction again on the way to bpf_exit
*/
new_sl = kmalloc(sizeof(struct verifier_state_list), GFP_USER);
if (!new_sl)
return -ENOMEM;
/* add new state to the head of linked list */
memcpy(&new_sl->state, &env->cur_state, sizeof(env->cur_state));
new_sl->next = env->explored_states[insn_idx];
env->explored_states[insn_idx] = new_sl;
return 0;
}
static int do_check(struct verifier_env *env)
{
struct verifier_state *state = &env->cur_state;
struct bpf_insn *insns = env->prog->insnsi;
struct reg_state *regs = state->regs;
int insn_cnt = env->prog->len;
int insn_idx, prev_insn_idx = 0;
int insn_processed = 0;
bool do_print_state = false;
init_reg_state(regs);
insn_idx = 0;
for (;;) {
struct bpf_insn *insn;
u8 class;
int err;
if (insn_idx >= insn_cnt) {
verbose("invalid insn idx %d insn_cnt %d\n",
insn_idx, insn_cnt);
return -EFAULT;
}
insn = &insns[insn_idx];
class = BPF_CLASS(insn->code);
if (++insn_processed > BPF_COMPLEXITY_LIMIT_INSNS) {
verbose("BPF program is too large. Proccessed %d insn\n",
insn_processed);
return -E2BIG;
}
err = is_state_visited(env, insn_idx);
if (err < 0)
return err;
if (err == 1) {
/* found equivalent state, can prune the search */
if (log_level) {
if (do_print_state)
verbose("\nfrom %d to %d: safe\n",
prev_insn_idx, insn_idx);
else
verbose("%d: safe\n", insn_idx);
}
goto process_bpf_exit;
}
if (log_level && do_print_state) {
verbose("\nfrom %d to %d:", prev_insn_idx, insn_idx);
print_verifier_state(&env->cur_state);
do_print_state = false;
}
if (log_level) {
verbose("%d: ", insn_idx);
print_bpf_insn(insn);
}
if (class == BPF_ALU || class == BPF_ALU64) {
err = check_alu_op(env, insn);
if (err)
return err;
} else if (class == BPF_LDX) {
enum bpf_reg_type src_reg_type;
/* check for reserved fields is already done */
/* check src operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
err = check_reg_arg(regs, insn->dst_reg, DST_OP_NO_MARK);
if (err)
return err;
src_reg_type = regs[insn->src_reg].type;
/* check that memory (src_reg + off) is readable,
* the state of dst_reg will be updated by this func
*/
err = check_mem_access(env, insn->src_reg, insn->off,
BPF_SIZE(insn->code), BPF_READ,
insn->dst_reg);
if (err)
return err;
if (BPF_SIZE(insn->code) != BPF_W) {
insn_idx++;
continue;
}
if (insn->imm == 0) {
/* saw a valid insn
* dst_reg = *(u32 *)(src_reg + off)
* use reserved 'imm' field to mark this insn
*/
insn->imm = src_reg_type;
} else if (src_reg_type != insn->imm &&
(src_reg_type == PTR_TO_CTX ||
insn->imm == PTR_TO_CTX)) {
/* ABuser program is trying to use the same insn
* dst_reg = *(u32*) (src_reg + off)
* with different pointer types:
* src_reg == ctx in one branch and
* src_reg == stack|map in some other branch.
* Reject it.
*/
verbose("same insn cannot be used with different pointers\n");
return -EINVAL;
}
} else if (class == BPF_STX) {
enum bpf_reg_type dst_reg_type;
if (BPF_MODE(insn->code) == BPF_XADD) {
err = check_xadd(env, insn);
if (err)
return err;
insn_idx++;
continue;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
/* check src2 operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
dst_reg_type = regs[insn->dst_reg].type;
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
insn->src_reg);
if (err)
return err;
if (insn->imm == 0) {
insn->imm = dst_reg_type;
} else if (dst_reg_type != insn->imm &&
(dst_reg_type == PTR_TO_CTX ||
insn->imm == PTR_TO_CTX)) {
verbose("same insn cannot be used with different pointers\n");
return -EINVAL;
}
} else if (class == BPF_ST) {
if (BPF_MODE(insn->code) != BPF_MEM ||
insn->src_reg != BPF_REG_0) {
verbose("BPF_ST uses reserved fields\n");
return -EINVAL;
}
/* check src operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
-1);
if (err)
return err;
} else if (class == BPF_JMP) {
u8 opcode = BPF_OP(insn->code);
if (opcode == BPF_CALL) {
if (BPF_SRC(insn->code) != BPF_K ||
insn->off != 0 ||
insn->src_reg != BPF_REG_0 ||
insn->dst_reg != BPF_REG_0) {
verbose("BPF_CALL uses reserved fields\n");
return -EINVAL;
}
err = check_call(env, insn->imm);
if (err)
return err;
} else if (opcode == BPF_JA) {
if (BPF_SRC(insn->code) != BPF_K ||
insn->imm != 0 ||
insn->src_reg != BPF_REG_0 ||
insn->dst_reg != BPF_REG_0) {
verbose("BPF_JA uses reserved fields\n");
return -EINVAL;
}
insn_idx += insn->off + 1;
continue;
} else if (opcode == BPF_EXIT) {
if (BPF_SRC(insn->code) != BPF_K ||
insn->imm != 0 ||
insn->src_reg != BPF_REG_0 ||
insn->dst_reg != BPF_REG_0) {
verbose("BPF_EXIT uses reserved fields\n");
return -EINVAL;
}
/* eBPF calling convetion is such that R0 is used
* to return the value from eBPF program.
* Make sure that it's readable at this time
* of bpf_exit, which means that program wrote
* something into it earlier
*/
err = check_reg_arg(regs, BPF_REG_0, SRC_OP);
if (err)
return err;
if (is_pointer_value(env, BPF_REG_0)) {
verbose("R0 leaks addr as return value\n");
return -EACCES;
}
process_bpf_exit:
insn_idx = pop_stack(env, &prev_insn_idx);
if (insn_idx < 0) {
break;
} else {
do_print_state = true;
continue;
}
} else {
err = check_cond_jmp_op(env, insn, &insn_idx);
if (err)
return err;
}
} else if (class == BPF_LD) {
u8 mode = BPF_MODE(insn->code);
if (mode == BPF_ABS || mode == BPF_IND) {
err = check_ld_abs(env, insn);
if (err)
return err;
} else if (mode == BPF_IMM) {
err = check_ld_imm(env, insn);
if (err)
return err;
insn_idx++;
} else {
verbose("invalid BPF_LD mode\n");
return -EINVAL;
}
} else {
verbose("unknown insn class %d\n", class);
return -EINVAL;
}
insn_idx++;
}
verbose("processed %d insns\n", insn_processed);
return 0;
}
/* look for pseudo eBPF instructions that access map FDs and
* replace them with actual map pointers
*/
static int replace_map_fd_with_map_ptr(struct verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
int i, j;
for (i = 0; i < insn_cnt; i++, insn++) {
if (BPF_CLASS(insn->code) == BPF_LDX &&
(BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
verbose("BPF_LDX uses reserved fields\n");
return -EINVAL;
}
if (BPF_CLASS(insn->code) == BPF_STX &&
((BPF_MODE(insn->code) != BPF_MEM &&
BPF_MODE(insn->code) != BPF_XADD) || insn->imm != 0)) {
verbose("BPF_STX uses reserved fields\n");
return -EINVAL;
}
if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
struct bpf_map *map;
struct fd f;
if (i == insn_cnt - 1 || insn[1].code != 0 ||
insn[1].dst_reg != 0 || insn[1].src_reg != 0 ||
insn[1].off != 0) {
verbose("invalid bpf_ld_imm64 insn\n");
return -EINVAL;
}
if (insn->src_reg == 0)
/* valid generic load 64-bit imm */
goto next_insn;
if (insn->src_reg != BPF_PSEUDO_MAP_FD) {
verbose("unrecognized bpf_ld_imm64 insn\n");
return -EINVAL;
}
f = fdget(insn->imm);
map = __bpf_map_get(f);
if (IS_ERR(map)) {
verbose("fd %d is not pointing to valid bpf_map\n",
insn->imm);
return PTR_ERR(map);
}
/* store map pointer inside BPF_LD_IMM64 instruction */
insn[0].imm = (u32) (unsigned long) map;
insn[1].imm = ((u64) (unsigned long) map) >> 32;
/* check whether we recorded this map already */
for (j = 0; j < env->used_map_cnt; j++)
if (env->used_maps[j] == map) {
fdput(f);
goto next_insn;
}
if (env->used_map_cnt >= MAX_USED_MAPS) {
fdput(f);
return -E2BIG;
}
/* hold the map. If the program is rejected by verifier,
* the map will be released by release_maps() or it
* will be used by the valid program until it's unloaded
* and all maps are released in free_bpf_prog_info()
*/
map = bpf_map_inc(map, false);
if (IS_ERR(map)) {
fdput(f);
return PTR_ERR(map);
}
env->used_maps[env->used_map_cnt++] = map;
fdput(f);
next_insn:
insn++;
i++;
}
}
/* now all pseudo BPF_LD_IMM64 instructions load valid
* 'struct bpf_map *' into a register instead of user map_fd.
* These pointers will be used later by verifier to validate map access.
*/
return 0;
}
/* drop refcnt of maps used by the rejected program */
static void release_maps(struct verifier_env *env)
{
int i;
for (i = 0; i < env->used_map_cnt; i++)
bpf_map_put(env->used_maps[i]);
}
/* convert pseudo BPF_LD_IMM64 into generic BPF_LD_IMM64 */
static void convert_pseudo_ld_imm64(struct verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
int i;
for (i = 0; i < insn_cnt; i++, insn++)
if (insn->code == (BPF_LD | BPF_IMM | BPF_DW))
insn->src_reg = 0;
}
/* convert load instructions that access fields of 'struct __sk_buff'
* into sequence of instructions that access fields of 'struct sk_buff'
*/
static int convert_ctx_accesses(struct verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
struct bpf_insn insn_buf[16];
struct bpf_prog *new_prog;
enum bpf_access_type type;
int i;
if (!env->prog->aux->ops->convert_ctx_access)
return 0;
for (i = 0; i < insn_cnt; i++, insn++) {
u32 insn_delta, cnt;
if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
type = BPF_READ;
else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
type = BPF_WRITE;
else
continue;
if (insn->imm != PTR_TO_CTX) {
/* clear internal mark */
insn->imm = 0;
continue;
}
cnt = env->prog->aux->ops->
convert_ctx_access(type, insn->dst_reg, insn->src_reg,
insn->off, insn_buf, env->prog);
if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
verbose("bpf verifier is misconfigured\n");
return -EINVAL;
}
new_prog = bpf_patch_insn_single(env->prog, i, insn_buf, cnt);
if (!new_prog)
return -ENOMEM;
insn_delta = cnt - 1;
/* keep walking new program and skip insns we just inserted */
env->prog = new_prog;
insn = new_prog->insnsi + i + insn_delta;
insn_cnt += insn_delta;
i += insn_delta;
}
return 0;
}
static void free_states(struct verifier_env *env)
{
struct verifier_state_list *sl, *sln;
int i;
if (!env->explored_states)
return;
for (i = 0; i < env->prog->len; i++) {
sl = env->explored_states[i];
if (sl)
while (sl != STATE_LIST_MARK) {
sln = sl->next;
kfree(sl);
sl = sln;
}
}
kfree(env->explored_states);
}
int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
{
char __user *log_ubuf = NULL;
struct verifier_env *env;
int ret = -EINVAL;
if ((*prog)->len <= 0 || (*prog)->len > BPF_MAXINSNS)
return -E2BIG;
/* 'struct verifier_env' can be global, but since it's not small,
* allocate/free it every time bpf_check() is called
*/
env = kzalloc(sizeof(struct verifier_env), GFP_KERNEL);
if (!env)
return -ENOMEM;
env->prog = *prog;
/* grab the mutex to protect few globals used by verifier */
mutex_lock(&bpf_verifier_lock);
if (attr->log_level || attr->log_buf || attr->log_size) {
/* user requested verbose verifier output
* and supplied buffer to store the verification trace
*/
log_level = attr->log_level;
log_ubuf = (char __user *) (unsigned long) attr->log_buf;
log_size = attr->log_size;
log_len = 0;
ret = -EINVAL;
/* log_* values have to be sane */
if (log_size < 128 || log_size > UINT_MAX >> 8 ||
log_level == 0 || log_ubuf == NULL)
goto free_env;
ret = -ENOMEM;
log_buf = vmalloc(log_size);
if (!log_buf)
goto free_env;
} else {
log_level = 0;
}
ret = replace_map_fd_with_map_ptr(env);
if (ret < 0)
goto skip_full_check;
env->explored_states = kcalloc(env->prog->len,
sizeof(struct verifier_state_list *),
GFP_USER);
ret = -ENOMEM;
if (!env->explored_states)
goto skip_full_check;
ret = check_cfg(env);
if (ret < 0)
goto skip_full_check;
env->allow_ptr_leaks = capable(CAP_SYS_ADMIN);
ret = do_check(env);
skip_full_check:
while (pop_stack(env, NULL) >= 0);
free_states(env);
if (ret == 0)
/* program is valid, convert *(u32*)(ctx + off) accesses */
ret = convert_ctx_accesses(env);
if (log_level && log_len >= log_size - 1) {
BUG_ON(log_len >= log_size);
/* verifier log exceeded user supplied buffer */
ret = -ENOSPC;
/* fall through to return what was recorded */
}
/* copy verifier log back to user space including trailing zero */
if (log_level && copy_to_user(log_ubuf, log_buf, log_len + 1) != 0) {
ret = -EFAULT;
goto free_log_buf;
}
if (ret == 0 && env->used_map_cnt) {
/* if program passed verifier, update used_maps in bpf_prog_info */
env->prog->aux->used_maps = kmalloc_array(env->used_map_cnt,
sizeof(env->used_maps[0]),
GFP_KERNEL);
if (!env->prog->aux->used_maps) {
ret = -ENOMEM;
goto free_log_buf;
}
memcpy(env->prog->aux->used_maps, env->used_maps,
sizeof(env->used_maps[0]) * env->used_map_cnt);
env->prog->aux->used_map_cnt = env->used_map_cnt;
/* program is valid. Convert pseudo bpf_ld_imm64 into generic
* bpf_ld_imm64 instructions
*/
convert_pseudo_ld_imm64(env);
}
free_log_buf:
if (log_level)
vfree(log_buf);
free_env:
if (!env->prog->aux->used_maps)
/* if we didn't copy map pointers into bpf_prog_info, release
* them now. Otherwise free_bpf_prog_info() will release them.
*/
release_maps(env);
*prog = env->prog;
kfree(env);
mutex_unlock(&bpf_verifier_lock);
return ret;
}
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