Re: [PATCH v2 bpf-next 0/4] Fix global subprog PTR_TO_CTX arg handling

[Eduard Zingerman <eddyz87@gmail.com>]

On Mon, 2024-02-12 at 15:32 -0800, Andrii Nakryiko wrote:
> Fix confusing and incorrect inference of PTR_TO_CTX argument type in BPF
> global subprogs. For some program types (iters, tracepoint, any program type
> that doesn't have fixed named "canonical" context type) when user uses (in
> a correct and valid way) a pointer argument to user-defined anonymous struct
> type, verifier will incorrectly assume that it has to be PTR_TO_CTX argument.
> While it should be just a PTR_TO_MEM argument with allowed size calculated
> from user-provided (even if anonymous) struct.
> 
> This did come up in practice and was very confusing to users, so let's prevent
> this going forward. We had to do a slight refactoring of
> btf_get_prog_ctx_type() to make it easy to support a special s390x KPROBE use
> cases. See details in respective patches.
> 
> v1->v2:
>   - special-case typedef bpf_user_pt_regs_t handling for KPROBE programs,
>     fixing s390x after changes in patch #2.
> 
> Andrii Nakryiko (4):
>   bpf: simplify btf_get_prog_ctx_type() into btf_is_prog_ctx_type()
>   bpf: handle bpf_user_pt_regs_t typedef explicitly for PTR_TO_CTX
>     global arg
>   bpf: don't infer PTR_TO_CTX for programs with unnamed context type
>   selftests/bpf: add anonymous user struct as global subprog arg test
> 
>  include/linux/btf.h                           | 17 ++++---
>  kernel/bpf/btf.c                              | 45 +++++++++++++------
>  kernel/bpf/verifier.c                         |  2 +-
>  .../bpf/progs/test_global_func_ctx_args.c     | 19 ++++++++
>  .../bpf/progs/verifier_global_subprogs.c      | 29 ++++++++++++
>  5 files changed, 88 insertions(+), 24 deletions(-)
> 

I have a nit for patch #2 but that might be not important.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>