bpf: make makr_btf_ld_reg return error for unexpected reg types

Non-functional change:
mark_btf_ld_reg() expects 'reg_type' parameter to be either
SCALAR_VALUE or PTR_TO_BTF_ID. Next commit expands this set, so update
this function to fail if unexpected type is passed. Also update
callers to propagate the error.

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250704230354.1323244-2-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 39 insertions, 20 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0f6cc2275695..9e8328f40b88 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2796,22 +2796,28 @@ static void mark_reg_not_init(struct bpf_verifier_env *env,
 	__mark_reg_not_init(env, regs + regno);
 }
 
-static void mark_btf_ld_reg(struct bpf_verifier_env *env,
-			    struct bpf_reg_state *regs, u32 regno,
-			    enum bpf_reg_type reg_type,
-			    struct btf *btf, u32 btf_id,
-			    enum bpf_type_flag flag)
+static int mark_btf_ld_reg(struct bpf_verifier_env *env,
+			   struct bpf_reg_state *regs, u32 regno,
+			   enum bpf_reg_type reg_type,
+			   struct btf *btf, u32 btf_id,
+			   enum bpf_type_flag flag)
 {
-	if (reg_type == SCALAR_VALUE) {
+	switch (reg_type) {
+	case SCALAR_VALUE:
 		mark_reg_unknown(env, regs, regno);
-		return;
+		return 0;
+	case PTR_TO_BTF_ID:
+		mark_reg_known_zero(env, regs, regno);
+		regs[regno].type = PTR_TO_BTF_ID | flag;
+		regs[regno].btf = btf;
+		regs[regno].btf_id = btf_id;
+		if (type_may_be_null(flag))
+			regs[regno].id = ++env->id_gen;
+		return 0;
+	default:
+		verifier_bug(env, "unexpected reg_type %d in %s\n", reg_type, __func__);
+		return -EFAULT;
 	}
-	mark_reg_known_zero(env, regs, regno);
-	regs[regno].type = PTR_TO_BTF_ID | flag;
-	regs[regno].btf = btf;
-	regs[regno].btf_id = btf_id;
-	if (type_may_be_null(flag))
-		regs[regno].id = ++env->id_gen;
 }
 
 #define DEF_NOT_SUBREG	(0)
@@ -5965,6 +5971,7 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
 	struct bpf_insn *insn = &env->prog->insnsi[insn_idx];
 	int class = BPF_CLASS(insn->code);
 	struct bpf_reg_state *val_reg;
+	int ret;
 
 	/* Things we already checked for in check_map_access and caller:
 	 *  - Reject cases where variable offset may touch kptr
@@ -5998,8 +6005,11 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
 		/* We can simply mark the value_regno receiving the pointer
 		 * value from map as PTR_TO_BTF_ID, with the correct type.
 		 */
-		mark_btf_ld_reg(env, cur_regs(env), value_regno, PTR_TO_BTF_ID, kptr_field->kptr.btf,
-				kptr_field->kptr.btf_id, btf_ld_kptr_type(env, kptr_field));
+		ret = mark_btf_ld_reg(env, cur_regs(env), value_regno, PTR_TO_BTF_ID,
+				      kptr_field->kptr.btf, kptr_field->kptr.btf_id,
+				      btf_ld_kptr_type(env, kptr_field));
+		if (ret < 0)
+			return ret;
 	} else if (class == BPF_STX) {
 		val_reg = reg_state(env, value_regno);
 		if (!register_is_null(val_reg) &&
@@ -7298,8 +7308,11 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
 		clear_trusted_flags(&flag);
 	}
 
-	if (atype == BPF_READ && value_regno >= 0)
-		mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id, flag);
+	if (atype == BPF_READ && value_regno >= 0) {
+		ret = mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id, flag);
+		if (ret < 0)
+			return ret;
+	}
 
 	return 0;
 }
@@ -7353,13 +7366,19 @@ static int check_ptr_to_map_access(struct bpf_verifier_env *env,
 
 	/* Simulate access to a PTR_TO_BTF_ID */
 	memset(&map_reg, 0, sizeof(map_reg));
-	mark_btf_ld_reg(env, &map_reg, 0, PTR_TO_BTF_ID, btf_vmlinux, *map->ops->map_btf_id, 0);
+	ret = mark_btf_ld_reg(env, &map_reg, 0, PTR_TO_BTF_ID,
+			      btf_vmlinux, *map->ops->map_btf_id, 0);
+	if (ret < 0)
+		return ret;
 	ret = btf_struct_access(&env->log, &map_reg, off, size, atype, &btf_id, &flag, NULL);
 	if (ret < 0)
 		return ret;
 
-	if (value_regno >= 0)
-		mark_btf_ld_reg(env, regs, value_regno, ret, btf_vmlinux, btf_id, flag);
+	if (value_regno >= 0) {
+		ret = mark_btf_ld_reg(env, regs, value_regno, ret, btf_vmlinux, btf_id, flag);
+		if (ret < 0)
+			return ret;
+	}
 
 	return 0;
 }