Re: [PATCH bpf-next v4 1/2] bpf: Support new pointer param types via SCALAR_VALUE for trampolines

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2026-03-10 at 23:16 +1100, Slava Imameev wrote:

[...]

> I verified whether PTR->FUNC, PTR->DATASEC, PTR->VAR can be passed to
> btf_ctx_access() in the current mainline.
> 
> I added helpers that inject PTR->FUNC, PTR->DATASEC, PTR->VAR as pre or
> post calls to btf_check_meta(). In all cases, the BPF program load
> failed with errors "arg0 type FUNC / DATASEC / VAR is not a struct",
> which indicates that btf_check_meta() can indeed be called with
> PTR->FUNC, PTR->DATASEC, PTR->VAR.
> 
> If the condition for pointer check is changed to
> `if (!btf_type_is_struct_ptr(btf, t))`, these BPF programs will load
> successfully with arguments set to scalar().
> 
> Do we accept this change in behavior?

Kernel validates BTF before loading, see kernel/bpf/btf.c:btf_resolve().
Validation is applied to kernel, module and program-level BTF.
Does BTF containing PTR->DATASEC and PTR->VAR pass validation?
If it does, validation should be updated to reject such cases.
For PTR->FUNC, which one is legit PTR->FUNC or PTR->FUNC_PROTO?
The legit one should be allowed and invalid should be rejected
at validation phase.

You can craft invalid BTF as in the following selftest:
tools/testing/selftests/bpf/prog_tests/btf.c.

[...]