[bpf-next,1/3] bpf: call btf_is_projection_of() conditionally

Commit Message

Maciej Fijalkowski Feb. 20, 2025, 1:45 p.m. UTC

Currently verifier thinks when sk_buff is used as kfunc's argument it is
coming as pointer to context (KF_ARG_PTR_TO_CTX) but in kfuncs that are
going to be introduced for sk_buff's refcount handling we want it to be
interpreted as KF_ARG_PTR_TO_BTF_ID.

Make it possible by calling btf_is_projection_of() conditionally.

Signed-off-by: Maciej Fijalkowski <[e-mail]>
---
 include/linux/btf.h   |  4 ++--
 kernel/bpf/btf.c      | 11 ++++++-----
 kernel/bpf/verifier.c |  3 ++-
 3 files changed, 10 insertions(+), 8 deletions(-)

Patch

diff --git a/include/linux/btf.h b/include/linux/btf.h
index ebc0c0c9b944..1307ea17542a 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -585,7 +585,7 @@  struct btf_struct_meta *btf_find_struct_meta(const struct btf *btf, u32 btf_id);
 bool btf_is_projection_of(const char *pname, const char *tname);
 bool btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
 			   const struct btf_type *t, enum bpf_prog_type prog_type,
-			   int arg);
+			   int arg, bool check_proj);
 int get_kern_ctx_btf_id(struct bpf_verifier_log *log, enum bpf_prog_type prog_type);
 bool btf_types_are_same(const struct btf *btf1, u32 id1,
 			const struct btf *btf2, u32 id2);
@@ -661,7 +661,7 @@  static inline struct btf_struct_meta *btf_find_struct_meta(const struct btf *btf
 static inline bool
 btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
 		     const struct btf_type *t, enum bpf_prog_type prog_type,
-		     int arg)
+		     int arg, bool check_proj)
 {
 	return false;
 }
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 69f5752e880b..62bdf6980cfb 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5909,7 +5909,7 @@  bool btf_is_projection_of(const char *pname, const char *tname)
 
 bool btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
 			  const struct btf_type *t, enum bpf_prog_type prog_type,
-			  int arg)
+			  int arg, bool check_proj)
 {
 	const struct btf_type *ctx_type;
 	const char *tname, *ctx_tname;
@@ -5969,8 +5969,9 @@  bool btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
 	 * int socket_filter_bpf_prog(struct __sk_buff *skb)
 	 * { // no fields of skb are ever used }
 	 */
-	if (btf_is_projection_of(ctx_tname, tname))
-		return true;
+	if (check_proj)
+		if (btf_is_projection_of(ctx_tname, tname))
+			return true;
 	if (strcmp(ctx_tname, tname)) {
 		/* bpf_user_pt_regs_t is a typedef, so resolve it to
 		 * underlying struct and check name again
@@ -6133,7 +6134,7 @@  static int btf_translate_to_vmlinux(struct bpf_verifier_log *log,
 				     enum bpf_prog_type prog_type,
 				     int arg)
 {
-	if (!btf_is_prog_ctx_type(log, btf, t, prog_type, arg))
+	if (!btf_is_prog_ctx_type(log, btf, t, prog_type, arg, true))
 		return -ENOENT;
 	return find_kern_ctx_type_id(prog_type);
 }
@@ -7739,7 +7740,7 @@  int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 		if (!btf_type_is_ptr(t))
 			goto skip_pointer;
 
-		if ((tags & ARG_TAG_CTX) || btf_is_prog_ctx_type(log, btf, t, prog_type, i)) {
+		if ((tags & ARG_TAG_CTX) || btf_is_prog_ctx_type(log, btf, t, prog_type, i, true)) {
 			if (tags & ~ARG_TAG_CTX) {
 				bpf_log(log, "arg#%d has invalid combination of tags\n", i);
 				return -EINVAL;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e57b7c949860..6492bfa4bc7a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11997,7 +11997,8 @@  get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
 	 * type to our caller. When a set of conditions hold in the BTF type of
 	 * arguments, we resolve it to a known kfunc_ptr_arg_type.
 	 */
-	if (btf_is_prog_ctx_type(&env->log, meta->btf, t, resolve_prog_type(env->prog), argno))
+	if (btf_is_prog_ctx_type(&env->log, meta->btf, t, resolve_prog_type(env->prog),
+				 argno, false))
 		return KF_ARG_PTR_TO_CTX;
 
 	if (is_kfunc_arg_nullable(meta->btf, &args[argno]) && register_is_null(reg))