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bpf, x64: fix stack layout of JITed bpf code

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Since commit 177366bf7c the %rbp stopped pointing to %rbp of the
previous stack frame. That broke frame pointer based stack unwinding.
This commit is a partial revert of it.
Note that the location of tail_call_cnt is fixed, since the verifier
enforces MAX_BPF_STACK stack size for programs with tail calls.

Fixes: 177366bf7c ("bpf: change x86 JITed program stack layout")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2019-06-14 15:43:28 -07:00
parent 86723c8640
commit fe8d9571dc
1 changed files with 21 additions and 53 deletions
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74
arch/x86/net/bpf_jit_comp.c
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@ -190,9 +190,7 @@ struct jit_context {
#define BPF_MAX_INSN_SIZE 128
#define BPF_INSN_SAFETY 64
#define AUX_STACK_SPACE 40 /* Space for RBX, R13, R14, R15, tailcnt */
#define PROLOGUE_SIZE 37
#define PROLOGUE_SIZE 20
/*
* Emit x86-64 prologue code for BPF program and check its size.
@ -203,44 +201,19 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf)
u8 *prog = *pprog;
int cnt = 0;
/* push rbp */
EMIT1(0x55);
/* mov rbp,rsp */
EMIT3(0x48, 0x89, 0xE5);
/* sub rsp, rounded_stack_depth + AUX_STACK_SPACE */
EMIT3_off32(0x48, 0x81, 0xEC,
round_up(stack_depth, 8) + AUX_STACK_SPACE);
/* sub rbp, AUX_STACK_SPACE */
EMIT4(0x48, 0x83, 0xED, AUX_STACK_SPACE);
/* mov qword ptr [rbp+0],rbx */
EMIT4(0x48, 0x89, 0x5D, 0);
/* mov qword ptr [rbp+8],r13 */
EMIT4(0x4C, 0x89, 0x6D, 8);
/* mov qword ptr [rbp+16],r14 */
EMIT4(0x4C, 0x89, 0x75, 16);
/* mov qword ptr [rbp+24],r15 */
EMIT4(0x4C, 0x89, 0x7D, 24);
EMIT1(0x55); /* push rbp */
EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */
/* sub rsp, rounded_stack_depth */
EMIT3_off32(0x48, 0x81, 0xEC, round_up(stack_depth, 8));
EMIT1(0x53); /* push rbx */
EMIT2(0x41, 0x55); /* push r13 */
EMIT2(0x41, 0x56); /* push r14 */
EMIT2(0x41, 0x57); /* push r15 */
if (!ebpf_from_cbpf) {
/*
* Clear the tail call counter (tail_call_cnt): for eBPF tail
* calls we need to reset the counter to 0. It's done in two
* instructions, resetting RAX register to 0, and moving it
* to the counter location.
*/
/* xor eax, eax */
EMIT2(0x31, 0xc0);
/* mov qword ptr [rbp+32], rax */
EMIT4(0x48, 0x89, 0x45, 32);
/* zero init tail_call_cnt */
EMIT2(0x6a, 0x00);
BUILD_BUG_ON(cnt != PROLOGUE_SIZE);
}
*pprog = prog;
}
@ -285,13 +258,13 @@ static void emit_bpf_tail_call(u8 **pprog)
* if (tail_call_cnt > MAX_TAIL_CALL_CNT)
* goto out;
*/
EMIT2_off32(0x8B, 0x85, 36); /* mov eax, dword ptr [rbp + 36] */
EMIT2_off32(0x8B, 0x85, -36 - MAX_BPF_STACK); /* mov eax, dword ptr [rbp - 548] */
EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */
#define OFFSET2 (30 + RETPOLINE_RAX_BPF_JIT_SIZE)
EMIT2(X86_JA, OFFSET2); /* ja out */
label2 = cnt;
EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */
EMIT2_off32(0x89, 0x85, 36); /* mov dword ptr [rbp + 36], eax */
EMIT2_off32(0x89, 0x85, -36 - MAX_BPF_STACK); /* mov dword ptr [rbp -548], eax */
/* prog = array->ptrs[index]; */
EMIT4_off32(0x48, 0x8B, 0x84, 0xD6, /* mov rax, [rsi + rdx * 8 + offsetof(...)] */
@ -1040,19 +1013,14 @@ emit_jmp:
seen_exit = true;
/* Update cleanup_addr */
ctx->cleanup_addr = proglen;
/* mov rbx, qword ptr [rbp+0] */
EMIT4(0x48, 0x8B, 0x5D, 0);
/* mov r13, qword ptr [rbp+8] */
EMIT4(0x4C, 0x8B, 0x6D, 8);
/* mov r14, qword ptr [rbp+16] */
EMIT4(0x4C, 0x8B, 0x75, 16);
/* mov r15, qword ptr [rbp+24] */
EMIT4(0x4C, 0x8B, 0x7D, 24);
/* add rbp, AUX_STACK_SPACE */
EMIT4(0x48, 0x83, 0xC5, AUX_STACK_SPACE);
EMIT1(0xC9); /* leave */
EMIT1(0xC3); /* ret */
if (!bpf_prog_was_classic(bpf_prog))
EMIT1(0x5B); /* get rid of tail_call_cnt */
EMIT2(0x41, 0x5F); /* pop r15 */
EMIT2(0x41, 0x5E); /* pop r14 */
EMIT2(0x41, 0x5D); /* pop r13 */
EMIT1(0x5B); /* pop rbx */
EMIT1(0xC9); /* leave */
EMIT1(0xC3); /* ret */
break;
default: