linux-kernel - Re: [PATCH v3 2/2] selftests/bpf: Add tests for alu on PTR_TO_FLOW

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Message-ID: <ea5b102e-2a4e-4363-a1d4-28e050ac9e1a@linux.dev>
Date: Fri, 12 Jan 2024 10:14:36 -0800
From: Yonghong Song <yonghong.song@...ux.dev>
To: Hao Sun <sunhao.th@...il.com>, bpf@...r.kernel.org
Cc: willemb@...gle.com, ast@...nel.org, andrii@...nel.org,
 daniel@...earbox.net, eddyz87@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] selftests/bpf: Add tests for alu on
 PTR_TO_FLOW_KEYS


On 1/12/24 7:20 AM, Hao Sun wrote:
> Add two cases for PTR_TO_FLOW_KEYS alu. One for rejecting alu with
> variable offset, another for fixed offset.
>
> Signed-off-by: Hao Sun <sunhao.th@...il.com>
> ---
>   .../bpf/progs/verifier_value_illegal_alu.c    | 36 +++++++++++++++++++
>   1 file changed, 36 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c b/tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c
> index 71814a753216..3bcccb4cbc85 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c
> @@ -146,4 +146,40 @@ l0_%=:	exit;						\
>   	: __clobber_all);
>   }
>   
> +SEC("flow_dissector")
> +__description("flow_keys illegal alu op with variable offset")
> +__failure __msg("R7 pointer arithmetic on flow_keys prohibited")
> +__naked void flow_keys_illegal_variable_offset_alu(void)
> +{
> +	asm volatile("					\
> +	r6 = r1;					\
> +	r7 = *(u64*)(r6 + %[flow_keys_off]);		\
> +	r8 = 8;						\
> +	r8 /= 1;					\
> +	r8 &= 8;					\
> +	r7 += r8;					\
> +	r0 = *(u64*)(r7 + 0);				\
> +	exit;						\
> +"	:
> +	: __imm_const(flow_keys_off, offsetof(struct __sk_buff, flow_keys))
> +	: __clobber_all);
> +}
> +
> +SEC("flow_dissector")
> +__description("flow_keys valid alu op with fixed offset")
> +__success
> +__naked void flow_keys_legal_fixed_offset_alu(void)
> +{
> +	asm volatile("					\
> +	r6 = r1;					\
> +	r7 = *(u64*)(r6 + %[flow_keys_off]);		\
> +	r8 = 8;						\
> +	r7 += r8;					\
> +	r0 = *(u64*)(r7 + 0);				\
> +	exit;						\
> +"	:
> +	: __imm_const(flow_keys_off, offsetof(struct __sk_buff, flow_keys))
> +	: __clobber_all);
> +}

Please remove the above '__success' case from this file. This file,
verifier_value_illegal_alu.c, only contains failure cases.

For the fixed offset, we already have C code to verify,
e.g., in bpf_flow.c.