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| author | Eduard Zingerman <eddyz87@gmail.com> | 2022-12-09 15:57:29 +0200 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-12-10 13:20:53 -0800 |
| commit | 5dd9cdbc9dec3e99b19e483767e247d15ca8cc0d (patch) | |
| tree | 7e4f61ea68eb44bd695a566e4e90df10de848dcb /kernel/bpf | |
| parent | cb578c1c9cf60275f258b5af7929c2a54a188f66 (diff) | |
| download | linux-5dd9cdbc9dec3e99b19e483767e247d15ca8cc0d.tar.bz2 | |
bpf: states_equal() must build idmap for all function frames
verifier.c:states_equal() must maintain register ID mapping across all
function frames. Otherwise the following example might be erroneously
marked as safe:
main:
fp[-24] = map_lookup_elem(...) ; frame[0].fp[-24].id == 1
fp[-32] = map_lookup_elem(...) ; frame[0].fp[-32].id == 2
r1 = &fp[-24]
r2 = &fp[-32]
call foo()
r0 = 0
exit
foo:
0: r9 = r1
1: r8 = r2
2: r7 = ktime_get_ns()
3: r6 = ktime_get_ns()
4: if (r6 > r7) goto skip_assign
5: r9 = r8
skip_assign: ; <--- checkpoint
6: r9 = *r9 ; (a) frame[1].r9.id == 2
; (b) frame[1].r9.id == 1
7: if r9 == 0 goto exit: ; mark_ptr_or_null_regs() transfers != 0 info
; for all regs sharing ID:
; (a) r9 != 0 => &frame[0].fp[-32] != 0
; (b) r9 != 0 => &frame[0].fp[-24] != 0
8: r8 = *r8 ; (a) r8 == &frame[0].fp[-32]
; (b) r8 == &frame[0].fp[-32]
9: r0 = *r8 ; (a) safe
; (b) unsafe
exit:
10: exit
While processing call to foo() verifier considers the following
execution paths:
(a) 0-10
(b) 0-4,6-10
(There is also path 0-7,10 but it is not interesting for the issue at
hand. (a) is verified first.)
Suppose that checkpoint is created at (6) when path (a) is verified,
next path (b) is verified and (6) is reached.
If states_equal() maintains separate 'idmap' for each frame the
mapping at (6) for frame[1] would be empty and
regsafe(r9)::check_ids() would add a pair 2->1 and return true,
which is an error.
If states_equal() maintains single 'idmap' for all frames the mapping
at (6) would be { 1->1, 2->2 } and regsafe(r9)::check_ids() would
return false when trying to add a pair 2->1.
This issue was suggested in the following discussion:
https://lore.kernel.org/bpf/CAEf4BzbFB5g4oUfyxk9rHy-PJSLQ3h8q9mV=rVoXfr_JVm8+1Q@mail.gmail.com/
Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20221209135733.28851-4-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/verifier.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 97645f767354..00c8e0a28203 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13260,7 +13260,6 @@ static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_stat { int i; - memset(env->idmap_scratch, 0, sizeof(env->idmap_scratch)); for (i = 0; i < MAX_BPF_REG; i++) if (!regsafe(env, &old->regs[i], &cur->regs[i], env->idmap_scratch)) @@ -13284,6 +13283,8 @@ static bool states_equal(struct bpf_verifier_env *env, if (old->curframe != cur->curframe) return false; + memset(env->idmap_scratch, 0, sizeof(env->idmap_scratch)); + /* Verification state from speculative execution simulation * must never prune a non-speculative execution one. */ |