bpf: verifier: refactor check_attach_btf_id()

The check_attach_btf_id() function really does three things:

1. It performs a bunch of checks on the program to ensure that the
   attachment is valid.

2. It stores a bunch of state about the attachment being requested in
   the verifier environment and struct bpf_prog objects.

3. It allocates a trampoline for the attachment.

This patch splits out (1.) and (3.) into separate functions which will
perform the checks, but return the computed values instead of directly
modifying the environment. This is done in preparation for reusing the
checks when the actual attachment is happening, which will allow tracing
programs to have multiple (compatible) attachments.

This also fixes a bug where a bunch of checks were skipped if a trampoline
already existed for the tracing target.

Fixes: 6ba43b761c41 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Fixes: 1e6c62a88215 ("bpf: Introduce sleepable BPF programs")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7bc9276c4ef4..363b4f1c562a 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -450,4 +450,17 @@ bpf_prog_offload_remove_insns(struct bpf_verifier_env *env, u32 off, u32 cnt);
 int check_ctx_reg(struct bpf_verifier_env *env,
 		  const struct bpf_reg_state *reg, int regno);
 
+/* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
+static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
+					     u32 btf_id)
+{
+        return tgt_prog ? (((u64)tgt_prog->aux->id) << 32 | btf_id) : btf_id;
+}
+
+int bpf_check_attach_target(struct bpf_verifier_log *log,
+			    const struct bpf_prog *prog,
+			    const struct bpf_prog *tgt_prog,
+			    u32 btf_id,
+			    struct bpf_attach_target_info *tgt_info);
+
 #endif /* _LINUX_BPF_VERIFIER_H */