Re: [PATCH bpf-next v2 0/2] bpf: Add multi-level pointer parameter support for trampolines

On Wed, 2026-02-18 at 09:13 +1100, Slava Imameev wrote:

[...]

The verifier assigns SCALAR type to single-level pointers (void*, int*).

So, the simplest change for pointers to pointers would be as below, right?

  --- a/kernel/bpf/btf.c
  +++ b/kernel/bpf/btf.c
  @@ -6906,7 +6906,8 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
           * If it's a pointer to void, it's the same as scalar from the verifier
           * safety POV. Either way, no futher pointer walking is allowed.
           */
  -       if (is_void_or_int_ptr(btf, t))
  +       if (is_void_or_int_ptr(btf, t) || !is_ptr_to_struct(btf, t))
                  return true;

          /* this is a pointer to another type */

Except that loaded value would be marked as scalar() and one would
need to cast it using e.g. bpf_core_cast() to obtain an untrusted
pointer.

For multi-level pointers, I selected PTR_TO_MEM to enable memory access
through a single load instruction for the first level of dereference,
with subsequent dereferences becoming SCALAR. This design eliminates
helper call for parameter dereference, replacing it with a load
instruction (e.g., void* ptr = *pptr).

If going this route instead, is there a technical reason to limit this
logic to multi-level pointers? Applying same rules to `int *` and
alike seem more consistent.

[...]