On Sun, Apr 13, 2025 at 01:06:25AM +0800, KaFai Wan wrote:
> Adding support to access arguments with const void pointer arguments
> in tracing programs.
>
> Currently we allow tracing programs to access void pointers. If we try to
> access argument which is pointer to const void like 2nd argument in kfree,
> verifier will fail to load the program with;
>
> 0: R1=ctx() R10=fp0
> ; asm volatile ("r2 = *(u64 *)(r1 + 8); ");
> 0: (79) r2 = *(u64 *)(r1 +8)
> func 'kfree' arg1 type UNKNOWN is not a struct
>
> Adding is_void_ptr to generic void pointer check.
>
> Cc: Leon Hwang <leon.hw...@linux.dev>
> Signed-off-by: KaFai Wan <kafai....@hotmail.com>
> ---
> kernel/bpf/btf.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 16ba36f34dfa..e11d3afd0562 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -6383,6 +6383,14 @@ struct btf *bpf_prog_get_target_btf(const struct
> bpf_prog *prog)
> return prog->aux->attach_btf;
> }
>
> +static bool is_void_ptr(struct btf *btf, const struct btf_type *t)
> +{
> + /* skip modifiers */
> + t = btf_type_skip_modifiers(btf, t->type, NULL);
> +
> + return t->type == 0;
I think you can use btf_type_is_void in here
> +}
> +
> static bool is_int_ptr(struct btf *btf, const struct btf_type *t)
> {
> /* skip modifiers */
> @@ -6776,7 +6784,7 @@ bool btf_ctx_access(int off, int size, enum
> bpf_access_type type,
> }
> }
>
> - if (t->type == 0)
> + if (is_void_ptr(btf, t))
lgtm,
nit, the is_void_ptr name suggest there's also ptr check in the helper function,
which is not the case. I understand it follows is_int_ptr name, but perhaps we
could rename both helpers to is_void and is_int ... feel free to ignore ;-)
jirka
> /* This is a pointer to void.
> * It is the same as scalar from the verifier safety pov.
> * No further pointer walking is allowed.
> --
> 2.43.0
>
