[PATCH bpf-next v4 03/13] bpf: Collect kfuncs after resolving program resources

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

The kfunc descriptors include argument prototypes generated while calls are
collected. Some argument classifications need program auxiliary state derived
from referenced maps, such as the arena associated with the program.

This avoids a footgun in get_kfunc_arg_type() checks where we do
validation on whether program has prog->aux->arena and it hasn't been
resolved yet.

check_and_resolve_insns() records used maps and populates that state. It must
remain after bpf_check_btf_info(), which applies kernel-side CO-RE relocations,
so that instruction validation and the program tag observe the relocated
instruction stream.

Move only add_kfuncs() after instruction and resource resolution. Subprogram
discovery and validation remain before the full BTF phase because that phase
needs the complete subprogram layout. Add a short comment describing the
resource resolution phase at the call site.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/verifier.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 24b163c2bd63..b62e77949542 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20344,11 +20344,6 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 	if (ret < 0)
 		goto skip_full_check;
 
-	/* Collect the kfunc descriptors used during verification. */
-	ret = add_kfuncs(env);
-	if (ret < 0)
-		goto skip_full_check;
-
 	ret = check_subprogs(env);
 	if (ret < 0)
 		goto skip_full_check;
@@ -20358,10 +20353,16 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 	if (ret < 0)
 		goto skip_full_check;
 
+	/* Validate instructions and resolve the program's referenced resources. */
 	ret = check_and_resolve_insns(env);
 	if (ret < 0)
 		goto skip_full_check;
 
+	/* Build kfunc prototypes after resolving program resources. */
+	ret = add_kfuncs(env);
+	if (ret < 0)
+		goto skip_full_check;
+
 	if (bpf_prog_is_offloaded(env->prog->aux)) {
 		ret = bpf_prog_offload_verifier_prep(env->prog);
 		if (ret)
-- 
2.53.0