bpf: add __arg_trusted global func arg tag

Add support for passing PTR_TO_BTF_ID registers to global subprogs.
Currently only PTR_TRUSTED flavor of PTR_TO_BTF_ID is supported.
Non-NULL semantics is assumed, so caller will be forced to prove
PTR_TO_BTF_ID can't be NULL.

Note, we disallow global subprogs to destroy passed in PTR_TO_BTF_ID
arguments, even the trusted one. We achieve that by not setting
ref_obj_id when validating subprog code. This basically enforces (in
Rust terms) borrowing semantics vs move semantics. Borrowing semantics
seems to be a better fit for isolated global subprog validation
approach.

Implementation-wise, we utilize existing logic for matching
user-provided BTF type to kernel-side BTF type, used by BPF CO-RE logic
and following same matching rules. We enforce a unique match for types.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240130000648.2144827-2-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7f5816482a10..0dcde339dc7e 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -610,6 +610,7 @@ struct bpf_subprog_arg_info {
 	enum bpf_arg_type arg_type;
 	union {
 		u32 mem_size;
+		u32 btf_id;
 	};
 };