linux-kernel - Re: [PATCH 1/2] bpf: Fix 32bit bounds update in ALU64

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Message-ID: <5d2addca-10e5-f7a6-9efd-43322eec8347@iogearbox.net>
Date:   Wed, 17 Aug 2022 22:31:30 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Youlin Li <liulin063@...il.com>, haoluo@...gle.com
Cc:     ast@...nel.org, john.fastabend@...il.com, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        kpsingh@...nel.org, sdf@...gle.com, jolsa@...nel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] bpf: Fix 32bit bounds update in ALU64

On 8/10/22 12:08 PM, Youlin Li wrote:
> The commit ("bpf: Do more tight ALU bounds tracking") introduces a bug
> that fails some selftests.
> 
> in previous versions of the code, when
> __reg_combine_64_into_32() was called, the 32bit boundary was
> completely deduced from the 64bit boundary, so there was a call to
> __mark_reg32_unbounded() in __reg_combine_64_into_32(). But before
> adjust_scalar_min_max_vals() calls
> __reg_combine_64_into_32() , the 32bit bounds are already calculated
> to some extent, and __mark_reg32_unbounded() will eliminate these
> information.
> 
> Simply remove the call to __reg_combine_64_into_32() and copying a code
> without __mark_reg32_unbounded() should work.
> 
> Before:
>      ./test_verifier 142
>      #142/p bounds check after truncation of non-boundary-crossing range FAIL
>      Failed to load prog 'Permission denied'!
>      invalid access to map value, value_size=8 off=16777215 size=1
>      R0 max value is outside of the allowed memory range
>      verification time 149 usec
>      stack depth 8
>      processed 15 insns (limit 1000000) max_states_per_insn 0
>      total_states 0 peak_states 0 mark_read 0
>      Summary: 0 PASSED, 1 SKIPPED, 1 FAILED
> 
> After:
>      ./test_verifier 142
>      #142/p bounds check after truncation of non-boundary-crossing range OK
>      Summary: 1 PASSED, 1 SKIPPED, 0 FAILED
> 
> Signed-off-by: Youlin Li <liulin063@...il.com>
> ---
>   kernel/bpf/verifier.c | 12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 11d8bb54ba6b..7ea6e0372d62 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -9014,7 +9014,17 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
>   		/* ALU32 ops are zero extended into 64bit register */
>   		zext_32_to_64(dst_reg);
>   	} else {
> -		__reg_combine_64_into_32(dst_reg);
> +		if (__reg64_bound_s32(dst_reg->smin_value) &&
> +		    __reg64_bound_s32(dst_reg->smax_value)) {
> +			dst_reg->s32_min_value = (s32)dst_reg->smin_value;
> +			dst_reg->s32_max_value = (s32)dst_reg->smax_value;
> +		}
> +		if (__reg64_bound_u32(dst_reg->umin_value) &&
> +		    __reg64_bound_u32(dst_reg->umax_value)) {
> +			dst_reg->u32_min_value = (u32)dst_reg->umin_value;
> +			dst_reg->u32_max_value = (u32)dst_reg->umax_value;
> +		}
> +		reg_bounds_sync(dst_reg);

Hm, this doesn't apply to the bpf tree. Is this on top of your previous patch [0]?
Please squash both together in that case and resubmit your previous one as a v2.

   [0] https://lore.kernel.org/bpf/9f954e67-67fc-e3b9-d810-22bfea95d2aa@iogearbox.net/

Thanks,
Daniel