Merge branch 'enhance-bpf-global-subprogs-with-argument-tags'

Andrii Nakryiko says:

====================
Enhance BPF global subprogs with argument tags

This patch set adds verifier support for annotating user's global BPF subprog
arguments with few commonly requested annotations, to improve global subprog
verification experience.

These tags are:
  - ability to annotate a special PTR_TO_CTX argument;
  - ability to annotate a generic PTR_TO_MEM as non-null.

We utilize btf_decl_tag attribute for this and provide two helper macros as
part of bpf_helpers.h in libbpf (patch #8).

Besides this we also add abilit to pass a pointer to dynptr into global
subprog. This is done based on type name match (struct bpf_dynptr *). This
allows to pass dynptrs into global subprogs, for use cases that deal with
variable-sized generic memory pointers.

Big chunk of the patch set (patches #1 through #5) are various refactorings to
make verifier internals around global subprog validation logic easier to
extend and support long term, eliminating BTF parsing logic duplication,
factoring out argument expectation definitions from BTF parsing, etc.

New functionality is added in patch #6 (ctx and non-null) and patch #7
(dynptr), extending global subprog checks with awareness for arg tags.

Patch #9 adds simple tests validating each of the added tags and dynptr
argument passing.

Patch #10 adds a simple negative case for freplace programs to make sure that
target BPF programs with "unreliable" BTF func proto cannot be freplaced.

v2->v3:
  - patch #10 improved by checking expected verifier error (Eduard);
v1->v2:
  - dropped packet args for now (Eduard);
  - added back unreliable=true detection for entry BPF programs (Eduard);
  - improved subprog arg validation (Eduard);
  - switched dynptr arg from tag to just type name based check (Eduard).
====================

Link: https://lore.kernel.org/r/20231215011334.2307144-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>