Re: [PATCH bpf-next] bpf: Fix propagation of bounds from 64-bit min/max into 32-bit and var_off.
From: Yonghong Song <hidden>
Date: 2021-10-29 18:29:22
Also in:
bpf
On 10/29/21 9:31 AM, Alexei Starovoitov wrote:
From: Alexei Starovoitov <ast@kernel.org>
Before this fix:
166: (b5) if r2 <= 0x1 goto pc+22
from 166 to 189: R2=invP(id=1,umax_value=1,var_off=(0x0; 0xffffffff))
After this fix:
166: (b5) if r2 <= 0x1 goto pc+22
from 166 to 189: R2=invP(id=1,umax_value=1,var_off=(0x0; 0x1))
While processing BPF_JLE the reg_set_min_max() would set true_reg->umax_value = 1
and call __reg_combine_64_into_32(true_reg).
Without the fix it would not pass the condition:
if (__reg64_bound_u32(reg->umin_value) && __reg64_bound_u32(reg->umax_value))
since umin_value == 0 at this point.
Before commit 10bf4e83167c the umin was incorrectly ingored.
The commit 10bf4e83167c fixed the correctness issue, but pessimized
propagation of 64-bit min max into 32-bit min max and corresponding var_off.
Fixes: 10bf4e83167c ("bpf: Fix propagation of 32 bit unsigned bounds from 64 bit bounds")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>See an unrelated nits below. Acked-by: Yonghong Song <redacted>
quoted hunk ↗ jump to hunk
--- kernel/bpf/verifier.c | 2 +- tools/testing/selftests/bpf/verifier/array_access.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 3c8aa7df1773..29671ed49ee8 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c@@ -1425,7 +1425,7 @@ static bool __reg64_bound_s32(s64 a)
We have
static bool __reg64_bound_s32(s64 a)
{
return a > S32_MIN && a < S32_MAX;
}
Should we change to
return a >= S32_MIN && a <= S32_MAX
?
quoted hunk ↗ jump to hunk
static bool __reg64_bound_u32(u64 a) { - return a > U32_MIN && a < U32_MAX; + return a >= U32_MIN && a <= U32_MAX; } static void __reg_combine_64_into_32(struct bpf_reg_state *reg)diff --git a/tools/testing/selftests/bpf/verifier/array_access.c b/tools/testing/selftests/bpf/verifier/array_access.c index 1b1c798e9248..1b138cd2b187 100644 --- a/tools/testing/selftests/bpf/verifier/array_access.c +++ b/tools/testing/selftests/bpf/verifier/array_access.c@@ -186,7 +186,7 @@ }, .fixup_map_hash_48b = { 3 }, .errstr_unpriv = "R0 leaks addr", - .errstr = "R0 unbounded memory access", + .errstr = "invalid access to map value, value_size=48 off=44 size=8", .result_unpriv = REJECT, .result = REJECT, .flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,