* [PATCH] bpf/verifier: fix control flow issues in __reg64_bound_u32()
@ 2022-07-29 5:49 Zeng Jingxiang
2022-07-29 17:15 ` Yonghong Song
0 siblings, 1 reply; 3+ messages in thread
From: Zeng Jingxiang @ 2022-07-29 5:49 UTC (permalink / raw)
To: ast, daniel, john.fastabend, andrii, martin.lau, song, yhs,
kpsingh, sdf, haoluo, jolsa
Cc: bpf, linux-kernel, Zeng Jingxiang
From: Zeng Jingxiang <linuszeng@tencent.com>
This greater-than-or-equal-to-zero comparison of an unsigned value
is always true. "a >= U32_MIN".
1632 return a >= U32_MIN && a <= U32_MAX;
Fixes: b9979db83401 ("bpf: Fix propagation of bounds from 64-bit min/max into 32-bit and var_off.")
Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
---
kernel/bpf/verifier.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0efbac0fd126..dd67108fb1d7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1629,7 +1629,7 @@ static bool __reg64_bound_s32(s64 a)
static bool __reg64_bound_u32(u64 a)
{
- return a >= U32_MIN && a <= U32_MAX;
+ return a <= U32_MAX;
}
static void __reg_combine_64_into_32(struct bpf_reg_state *reg)
--
2.27.0
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] bpf/verifier: fix control flow issues in __reg64_bound_u32()
2022-07-29 5:49 [PATCH] bpf/verifier: fix control flow issues in __reg64_bound_u32() Zeng Jingxiang
@ 2022-07-29 17:15 ` Yonghong Song
2022-07-29 17:17 ` Hao Luo
0 siblings, 1 reply; 3+ messages in thread
From: Yonghong Song @ 2022-07-29 17:15 UTC (permalink / raw)
To: Zeng Jingxiang, ast, daniel, john.fastabend, andrii, martin.lau,
song, kpsingh, sdf, haoluo, jolsa
Cc: bpf, linux-kernel, Zeng Jingxiang
On 7/28/22 10:49 PM, Zeng Jingxiang wrote:
> From: Zeng Jingxiang <linuszeng@tencent.com>
>
> This greater-than-or-equal-to-zero comparison of an unsigned value
> is always true. "a >= U32_MIN".
> 1632 return a >= U32_MIN && a <= U32_MAX;
>
> Fixes: b9979db83401 ("bpf: Fix propagation of bounds from 64-bit min/max into 32-bit and var_off.")
> Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
> ---
> kernel/bpf/verifier.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 0efbac0fd126..dd67108fb1d7 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1629,7 +1629,7 @@ static bool __reg64_bound_s32(s64 a)
>
> static bool __reg64_bound_u32(u64 a)
> {
> - return a >= U32_MIN && a <= U32_MAX;
> + return a <= U32_MAX;
> }
I cannot find the related link. But IIRC, Alexei commented that
the code is written this way to express the intention (within
32bit bounds) so this patch is unnecessary...
>
> static void __reg_combine_64_into_32(struct bpf_reg_state *reg)
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] bpf/verifier: fix control flow issues in __reg64_bound_u32()
2022-07-29 17:15 ` Yonghong Song
@ 2022-07-29 17:17 ` Hao Luo
0 siblings, 0 replies; 3+ messages in thread
From: Hao Luo @ 2022-07-29 17:17 UTC (permalink / raw)
To: Yonghong Song
Cc: Zeng Jingxiang, ast, daniel, john.fastabend, andrii, martin.lau,
song, kpsingh, sdf, jolsa, bpf, linux-kernel, Zeng Jingxiang
On Fri, Jul 29, 2022 at 10:15 AM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 7/28/22 10:49 PM, Zeng Jingxiang wrote:
> > From: Zeng Jingxiang <linuszeng@tencent.com>
> >
> > This greater-than-or-equal-to-zero comparison of an unsigned value
> > is always true. "a >= U32_MIN".
> > 1632 return a >= U32_MIN && a <= U32_MAX;
> >
> > Fixes: b9979db83401 ("bpf: Fix propagation of bounds from 64-bit min/max into 32-bit and var_off.")
> > Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
> > ---
> > kernel/bpf/verifier.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 0efbac0fd126..dd67108fb1d7 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -1629,7 +1629,7 @@ static bool __reg64_bound_s32(s64 a)
> >
> > static bool __reg64_bound_u32(u64 a)
> > {
> > - return a >= U32_MIN && a <= U32_MAX;
> > + return a <= U32_MAX;
> > }
>
> I cannot find the related link. But IIRC, Alexei commented that
> the code is written this way to express the intention (within
> 32bit bounds) so this patch is unnecessary...
>
Yeah, I agree with Yonghong. I was about to reply.
Jingxiang, you are absolutely correct that a <= U32_MAX is redundant,
but I feel having both sides checked explicitly makes code more
readable.
> >
> > static void __reg_combine_64_into_32(struct bpf_reg_state *reg)
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-07-29 17:17 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2022-07-29 5:49 [PATCH] bpf/verifier: fix control flow issues in __reg64_bound_u32() Zeng Jingxiang
2022-07-29 17:15 ` Yonghong Song
2022-07-29 17:17 ` Hao Luo
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