bpf: prepare btf_prepare_func_args() for handling static subprogs

Generalize btf_prepare_func_args() to support both global and static
subprogs. We are going to utilize this property in the next patch,
reusing btf_prepare_func_args() for subprog call logic instead of
reparsing BTF information in a completely separate implementation.

btf_prepare_func_args() now detects whether subprog is global or static
makes slight logic adjustments for static func cases, like not failing
fatally (-EFAULT) for conditions that are allowable for static subprogs.

Somewhat subtle (but major!) difference is the handling of pointer arguments.
Both global and static functions need to handle special context
arguments (which are pointers to predefined type names), but static
subprogs give up on any other pointers, falling back to marking subprog
as "unreliable", disabling the use of BTF type information altogether.

For global functions, though, we are assuming that such pointers to
unrecognized types are just pointers to fixed-sized memory region (or
error out if size cannot be established, like for `void *` pointers).

This patch accommodates these small differences and sets up a stage for
refactoring in the next patch, eliminating a separate BTF-based parsing
logic in btf_check_func_arg_match().

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231215011334.2307144-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 5742e9c0a7b8..d3ea9ef04767 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -738,6 +738,11 @@ struct bpf_verifier_env {
 	char tmp_str_buf[TMP_STR_BUF_LEN];
 };
 
+static inline struct bpf_func_info_aux *subprog_aux(struct bpf_verifier_env *env, int subprog)
+{
+	return &env->prog->aux->func_info_aux[subprog];
+}
+
 static inline struct bpf_subprog_info *subprog_info(struct bpf_verifier_env *env, int subprog)
 {
 	return &env->subprog_info[subprog];