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selftests/bpf: verify states_equal() maintains idmap across all frames

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A test case that would erroneously pass verification if
verifier.c:states_equal() maintains separate register ID mappings for
call frames.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20221209135733.28851-5-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Eduard Zingerman 2022-12-09 15:57:30 +02:00 committed by Alexei Starovoitov
parent 5dd9cdbc9d
commit 7d05794330
1 changed files with 82 additions and 0 deletions
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82
tools/testing/selftests/bpf/verifier/calls.c
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@ -2305,3 +2305,85 @@
.errstr = "!read_ok",
.result = REJECT,
},
/* Make sure that verifier.c:states_equal() considers IDs from all
* frames when building 'idmap' for check_ids().
*/
{
"calls: check_ids() across call boundary",
.insns = {
/* Function main() */
BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
/* fp[-24] = map_lookup_elem(...) ; get a MAP_VALUE_PTR_OR_NULL with some ID */
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
BPF_LD_MAP_FD(BPF_REG_1,
0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_0, -24),
/* fp[-32] = map_lookup_elem(...) ; get a MAP_VALUE_PTR_OR_NULL with some ID */
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
BPF_LD_MAP_FD(BPF_REG_1,
0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_0, -32),
/* call foo(&fp[-24], &fp[-32]) ; both arguments have IDs in the current
* ; stack frame
*/
BPF_MOV64_REG(BPF_REG_1, BPF_REG_FP),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -24),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_FP),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -32),
BPF_CALL_REL(2),
/* exit 0 */
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
/* Function foo()
*
* r9 = &frame[0].fp[-24] ; save arguments in the callee saved registers,
* r8 = &frame[0].fp[-32] ; arguments are pointers to pointers to map value
*/
BPF_MOV64_REG(BPF_REG_9, BPF_REG_1),
BPF_MOV64_REG(BPF_REG_8, BPF_REG_2),
/* r7 = ktime_get_ns() */
BPF_EMIT_CALL(BPF_FUNC_ktime_get_ns),
BPF_MOV64_REG(BPF_REG_7, BPF_REG_0),
/* r6 = ktime_get_ns() */
BPF_EMIT_CALL(BPF_FUNC_ktime_get_ns),
BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
/* if r6 > r7 goto +1 ; no new information about the state is derived from
* ; this check, thus produced verifier states differ
* ; only in 'insn_idx'
* r9 = r8
*/
BPF_JMP_REG(BPF_JGT, BPF_REG_6, BPF_REG_7, 1),
BPF_MOV64_REG(BPF_REG_9, BPF_REG_8),
/* r9 = *r9 ; verifier get's to this point via two paths:
* ; (I) one including r9 = r8, verified first;
* ; (II) one excluding r9 = r8, verified next.
* ; After load of *r9 to r9 the frame[0].fp[-24].id == r9.id.
* ; Suppose that checkpoint is created here via path (I).
* ; When verifying via (II) the r9.id must be compared against
* ; frame[0].fp[-24].id, otherwise (I) and (II) would be
* ; incorrectly deemed equivalent.
* if r9 == 0 goto <exit>
*/
BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_9, 0),
BPF_JMP_IMM(BPF_JEQ, BPF_REG_9, 0, 1),
/* r8 = *r8 ; read map value via r8, this is not safe
* r0 = *r8 ; because r8 might be not equal to r9.
*/
BPF_LDX_MEM(BPF_DW, BPF_REG_8, BPF_REG_8, 0),
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_8, 0),
/* exit 0 */
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.flags = BPF_F_TEST_STATE_FREQ,
.fixup_map_hash_8b = { 3, 9 },
.result = REJECT,
.errstr = "R8 invalid mem access 'map_value_or_null'",
.result_unpriv = REJECT,
.errstr_unpriv = "",
.prog_type = BPF_PROG_TYPE_CGROUP_SKB,
},