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Message-ID: <CAEf4BzYN2Mdx6zY01Uq3Kod41j96H3WfuN=PjCcOO=ZrUbVB9w@mail.gmail.com>
Date: Tue, 19 Dec 2023 10:42:03 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: andrii@...nel.org, eddyz87@...il.com, yonghong.song@...ux.dev,
alexei.starovoitov@...il.com, ast@...nel.org, daniel@...earbox.net,
john.fastabend@...il.com, martin.lau@...ux.dev, song@...nel.org,
kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
mykolal@...com, shuah@...nel.org, bpf@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 4/4] selftests/bpf: add testcase to
verifier_bounds.c for BPF_JNE
On Tue, Dec 19, 2023 at 5:51 AM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> Add testcase for the logic that the verifier tracks the BPF_JNE for regs.
> The assembly function "reg_not_equal_const()" and "reg_equal_const" that
> we add is exactly converted from the following case:
>
> u32 a = bpf_get_prandom_u32();
> u64 b = 0;
>
> a %= 8;
> /* the "a > 0" here will be optimized to "a != 0" */
> if (a > 0) {
> /* now the range of a should be [1, 7] */
> bpf_skb_store_bytes(skb, 0, &b, a, 0);
> }
>
> Signed-off-by: Menglong Dong <menglong8.dong@...il.com>
> ---
> v5:
> - add some comments to the function that we add
> - add reg_not_equal_const()
> ---
> .../selftests/bpf/progs/verifier_bounds.c | 62 +++++++++++++++++++
> 1 file changed, 62 insertions(+)
>
LGTM
Acked-by: Andrii Nakryiko <andrii@...nel.org>
> diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> index ec430b71730b..960998f16306 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
> @@ -1075,4 +1075,66 @@ l0_%=: r0 = 0; \
> : __clobber_all);
> }
>
> +SEC("tc")
> +__description("bounds check with JMP_NE for reg edge")
> +__success __retval(0)
> +__naked void reg_not_equal_const(void)
> +{
> + asm volatile (" \
> + r6 = r1; \
> + r1 = 0; \
> + *(u64*)(r10 - 8) = r1; \
> + call %[bpf_get_prandom_u32]; \
> + r4 = r0; \
> + r4 &= 7; \
> + if r4 != 0 goto l0_%=; \
> + r0 = 0; \
> + exit; \
> +l0_%=: r1 = r6; \
> + r2 = 0; \
> + r3 = r10; \
> + r3 += -8; \
> + r5 = 0; \
> + /* The 4th argument of bpf_skb_store_bytes is defined as \
> + * ARG_CONST_SIZE, so 0 is not allowed. The 'r4 != 0' \
> + * is providing us this exclusion of zero from initial \
> + * [0, 7] range. \
> + */ \
> + call %[bpf_skb_store_bytes]; \
> + r0 = 0; \
> + exit; \
> +" :
> + : __imm(bpf_get_prandom_u32),
> + __imm(bpf_skb_store_bytes)
> + : __clobber_all);
> +}
> +
> +SEC("tc")
> +__description("bounds check with JMP_EQ for reg edge")
> +__success __retval(0)
> +__naked void reg_equal_const(void)
> +{
> + asm volatile (" \
> + r6 = r1; \
> + r1 = 0; \
> + *(u64*)(r10 - 8) = r1; \
> + call %[bpf_get_prandom_u32]; \
> + r4 = r0; \
> + r4 &= 7; \
> + if r4 == 0 goto l0_%=; \
> + r1 = r6; \
> + r2 = 0; \
> + r3 = r10; \
> + r3 += -8; \
> + r5 = 0; \
> + /* Just the same as what we do in reg_not_equal_const() */ \
> + call %[bpf_skb_store_bytes]; \
> +l0_%=: r0 = 0; \
> + exit; \
> +" :
> + : __imm(bpf_get_prandom_u32),
> + __imm(bpf_skb_store_bytes)
> + : __clobber_all);
> +}
> +
> char _license[] SEC("license") = "GPL";
> --
> 2.39.2
>
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