Re: [PATCH bpf 2/2] bpf: Require ARG_PTR_TO_MEM with memory flag

[Zesen Liu <ftyghome@gmail.com>]

Hi,

It seems my mail server blocked the cover letter (0/2) of this patchset. Please ignore this thread, I will resend the complete series.
Sorry for the noise.

Thanks,
Zesen Liu

> On Jan 7, 2026, at 20:16, Zesen Liu <ftyghome@gmail.com> wrote:
> 
> Add check to ensure that ARG_PTR_TO_MEM is used with either MEM_WRITE or
> MEM_RDONLY.
> 
> Using ARG_PTR_TO_MEM alone without tags does not make sense because:
> 
> - If the helper does not change the argument, missing MEM_RDONLY causes the
> verifier to incorrectly reject a read-only buffer.
> - If the helper does change the argument, missing MEM_WRITE causes the
> verifier to incorrectly assume the memory is unchanged, leading to errors
> in code optimization.
> 
> Co-developed-by: Shuran Liu <electronlsr@gmail.com>
> Signed-off-by: Shuran Liu <electronlsr@gmail.com>
> Co-developed-by: Peili Gao <gplhust955@gmail.com>
> Signed-off-by: Peili Gao <gplhust955@gmail.com>
> Co-developed-by: Haoran Ni <haoran.ni.cs@gmail.com>
> Signed-off-by: Haoran Ni <haoran.ni.cs@gmail.com>
> Signed-off-by: Zesen Liu <ftyghome@gmail.com>
> ---
> kernel/bpf/verifier.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index f0ca69f888fa..c7ebddb66385 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -10349,10 +10349,27 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn)
> return true;
> }
> 
> +static bool check_mem_arg_rw_flag_ok(const struct bpf_func_proto *fn)
> +{
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {
> + enum bpf_arg_type arg_type = fn->arg_type[i];
> +
> + if (base_type(arg_type) != ARG_PTR_TO_MEM)
> + continue;
> + if (!(arg_type & (MEM_WRITE | MEM_RDONLY)))
> + return false;
> + }
> +
> + return true;
> +}
> +
> static int check_func_proto(const struct bpf_func_proto *fn, int func_id)
> {
> return check_raw_mode_ok(fn) &&
>       check_arg_pair_ok(fn) &&
> +   check_mem_arg_rw_flag_ok(fn) &&
>       check_btf_id_ok(fn) ? 0 : -EINVAL;
> }
> 
> 
> -- 
> 2.43.0
>