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

[Slava Imameev <slava.imameev@crowdstrike.com>]

On 2026-03-03 20:05 UTC, Eduard Zingerman wrote:

> > @@ -6902,11 +6921,7 @@ 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_ptr_treated_as_scalar(btf, t))
> >               return true;
> 
> I'm probably missing a point here, but what's wrong with Alexei's
> suggestion to do this instead:
> 
>         if (is_ptr_treated_as_scalar(btf, t))
>                  return true;
> ?

This reflects my belief in a cautious approach: adding support
only for selected types with tests added for each new type. That said,
I can add the suggested broader condition and make it pass the tests,
but I cannot be sure it will be future-proof against conflicts.

I think the broader check like

	/* skip modifiers */
	tt = t;
	while (btf_type_is_modifier(tt))
		tt = btf_type_by_id(btf, tt->type);
	if (!btf_type_is_struct(tt))
		return true;

might have some incompatibility with future changes, compared to
explicit type checks for selected types. This condition is
open-ended, including anything instead of selecting specific types.

This broader check also needs to be moved down closer to the exit
from btf_ctx_access; otherwise, btf_ctx_access can exit early
without executing the following code. In my case, this resulted in
existing test failures if the above !btf_type_is_struct(tt) replaces
current master's branch condition

	if (is_void_or_int_ptr(btf, t))
		return true;

The result for: 

./vmtest.sh -- ./test_progs

was:

	Summary: 617/5770 PASSED, 80 SKIPPED, 82 FAILED

with a lot of:

	unexpected_load_success

Compared to:

	Summary: 692/6045 PASSED, 80 SKIPPED, 7 FAILED

for the master branch.

As I noted this diff, closer to the exit from btf_ctx_access,
makes tests to pass:

        if (!btf_type_is_struct(t)) {
-               bpf_log(log,
-                       "func '%s' arg%d type %s is not a struct\n",
-                       tname, arg, btf_type_str(t));
-               return false;
+               info->reg_type = SCALAR_VALUE;
+               return true;
        }


> Only two new tests fail:
> - #554/62  verifier_ctx_ptr_param/fentry/pointer to float - invalid ctx access:FAIL
> - #554/63  verifier_ctx_ptr_param/fentry/double pointer to float - invalid ctx access:FAIL

> But I'd say this shouldn't matter.
> This will also make selftests much simpler.

Yes, I decided not to add support for pointers to float.