bpf: Refactor btf_struct_access

Instead of having to pass multiple arguments that describe the register,
pass the bpf_reg_state into the btf_struct_access callback. Currently,
all call sites simply reuse the btf and btf_id of the reg they want to
check the access of. The only exception to this pattern is the callsite
in check_ptr_to_map_access, hence for that case create a dummy reg to
simulate PTR_TO_BTF_ID access.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221114191547.1694267-8-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -771,6 +771,7 @@ struct bpf_prog_ops {
 			union bpf_attr __user *uattr);
 };
 
+struct bpf_reg_state;
 struct bpf_verifier_ops {
 	/* return eBPF function prototype for verification */
 	const struct bpf_func_proto *
@@ -792,9 +793,8 @@ struct bpf_verifier_ops {
 				  struct bpf_insn *dst,
 				  struct bpf_prog *prog, u32 *target_size);
 	int (*btf_struct_access)(struct bpf_verifier_log *log,
-				 const struct btf *btf,
+				 const struct bpf_reg_state *reg,
-				 const struct btf_type *t, int off, int size,
+				 int off, int size, enum bpf_access_type atype,
-				 enum bpf_access_type atype,
 				 u32 *next_btf_id, enum bpf_type_flag *flag);
 };
 
@@ -2080,9 +2080,9 @@ static inline bool bpf_tracing_btf_ctx_access(int off, int size,
 	return btf_ctx_access(off, size, type, prog, info);
 }
 
-int btf_struct_access(struct bpf_verifier_log *log, const struct btf *btf,
+int btf_struct_access(struct bpf_verifier_log *log,
-		      const struct btf_type *t, int off, int size,
+		      const struct bpf_reg_state *reg,
-		      enum bpf_access_type atype,
+		      int off, int size, enum bpf_access_type atype,
 		      u32 *next_btf_id, enum bpf_type_flag *flag);
 bool btf_struct_ids_match(struct bpf_verifier_log *log,
 			  const struct btf *btf, u32 id, int off,
@@ -2333,9 +2333,8 @@ static inline struct bpf_prog *bpf_prog_by_id(u32 id)
 }
 
 static inline int btf_struct_access(struct bpf_verifier_log *log,
-				    const struct btf *btf,
+				    const struct bpf_reg_state *reg,
-				    const struct btf_type *t, int off, int size,
+				    int off, int size, enum bpf_access_type atype,
-				    enum bpf_access_type atype,
 				    u32 *next_btf_id, enum bpf_type_flag *flag)
 {
 	return -EACCES;

include/linux/filter.h

@@ -568,10 +568,10 @@ struct sk_filter {
 DECLARE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
 
 extern struct mutex nf_conn_btf_access_lock;
-extern int (*nfct_btf_struct_access)(struct bpf_verifier_log *log, const struct btf *btf,
+extern int (*nfct_btf_struct_access)(struct bpf_verifier_log *log,
-				     const struct btf_type *t, int off, int size,
+				     const struct bpf_reg_state *reg,
-				     enum bpf_access_type atype, u32 *next_btf_id,
+				     int off, int size, enum bpf_access_type atype,
-				     enum bpf_type_flag *flag);
+				     u32 *next_btf_id, enum bpf_type_flag *flag);
 
 typedef unsigned int (*bpf_dispatcher_fn)(const void *ctx,
 					  const struct bpf_insn *insnsi,

kernel/bpf/btf.c

@@ -6017,15 +6017,18 @@ error:
 	return -EINVAL;
 }
 
-int btf_struct_access(struct bpf_verifier_log *log, const struct btf *btf,
+int btf_struct_access(struct bpf_verifier_log *log,
-		      const struct btf_type *t, int off, int size,
+		      const struct bpf_reg_state *reg,
-		      enum bpf_access_type atype __maybe_unused,
+		      int off, int size, enum bpf_access_type atype __maybe_unused,
 		      u32 *next_btf_id, enum bpf_type_flag *flag)
 {
+	const struct btf *btf = reg->btf;
 	enum bpf_type_flag tmp_flag = 0;
+	const struct btf_type *t;
+	u32 id = reg->btf_id;
 	int err;
-	u32 id;
 
+	t = btf_type_by_id(btf, id);
 	do {
 		err = btf_struct_walk(log, btf, t, off, size, &id, &tmp_flag);
 

kernel/bpf/verifier.c

@@ -4688,16 +4688,14 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
 	}
 
 	if (env->ops->btf_struct_access) {
-		ret = env->ops->btf_struct_access(&env->log, reg->btf, t,
+		ret = env->ops->btf_struct_access(&env->log, reg, off, size, atype, &btf_id, &flag);
-						  off, size, atype, &btf_id, &flag);
 	} else {
 		if (atype != BPF_READ) {
 			verbose(env, "only read is supported\n");
 			return -EACCES;
 		}
 
-		ret = btf_struct_access(&env->log, reg->btf, t, off, size,
+		ret = btf_struct_access(&env->log, reg, off, size, atype, &btf_id, &flag);
-					atype, &btf_id, &flag);
 	}
 
 	if (ret < 0)
@@ -4723,6 +4721,7 @@ static int check_ptr_to_map_access(struct bpf_verifier_env *env,
 {
 	struct bpf_reg_state *reg = regs + regno;
 	struct bpf_map *map = reg->map_ptr;
+	struct bpf_reg_state map_reg;
 	enum bpf_type_flag flag = 0;
 	const struct btf_type *t;
 	const char *tname;
@@ -4761,7 +4760,10 @@ static int check_ptr_to_map_access(struct bpf_verifier_env *env,
 		return -EACCES;
 	}
 
-	ret = btf_struct_access(&env->log, btf_vmlinux, t, off, size, atype, &btf_id, &flag);
+	/* 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 = btf_struct_access(&env->log, &map_reg, off, size, atype, &btf_id, &flag);
 	if (ret < 0)
 		return ret;
 

net/bpf/bpf_dummy_struct_ops.c

@@ -156,29 +156,29 @@ static bool bpf_dummy_ops_is_valid_access(int off, int size,
 }
 
 static int bpf_dummy_ops_btf_struct_access(struct bpf_verifier_log *log,
-					   const struct btf *btf,
+					   const struct bpf_reg_state *reg,
-					   const struct btf_type *t, int off,
+					   int off, int size, enum bpf_access_type atype,
-					   int size, enum bpf_access_type atype,
 					   u32 *next_btf_id,
 					   enum bpf_type_flag *flag)
 {
 	const struct btf_type *state;
+	const struct btf_type *t;
 	s32 type_id;
 	int err;
 
-	type_id = btf_find_by_name_kind(btf, "bpf_dummy_ops_state",
+	type_id = btf_find_by_name_kind(reg->btf, "bpf_dummy_ops_state",
 					BTF_KIND_STRUCT);
 	if (type_id < 0)
 		return -EINVAL;
 
-	state = btf_type_by_id(btf, type_id);
+	t = btf_type_by_id(reg->btf, reg->btf_id);
+	state = btf_type_by_id(reg->btf, type_id);
 	if (t != state) {
 		bpf_log(log, "only access to bpf_dummy_ops_state is supported\n");
 		return -EACCES;
 	}
 
-	err = btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+	err = btf_struct_access(log, reg, off, size, atype, next_btf_id, flag);
-				flag);
 	if (err < 0)
 		return err;
 

net/core/filter.c

@@ -8651,28 +8651,25 @@ static bool tc_cls_act_is_valid_access(int off, int size,
 DEFINE_MUTEX(nf_conn_btf_access_lock);
 EXPORT_SYMBOL_GPL(nf_conn_btf_access_lock);
 
-int (*nfct_btf_struct_access)(struct bpf_verifier_log *log, const struct btf *btf,
+int (*nfct_btf_struct_access)(struct bpf_verifier_log *log,
-			      const struct btf_type *t, int off, int size,
+			      const struct bpf_reg_state *reg,
-			      enum bpf_access_type atype, u32 *next_btf_id,
+			      int off, int size, enum bpf_access_type atype,
-			      enum bpf_type_flag *flag);
+			      u32 *next_btf_id, enum bpf_type_flag *flag);
 EXPORT_SYMBOL_GPL(nfct_btf_struct_access);
 
 static int tc_cls_act_btf_struct_access(struct bpf_verifier_log *log,
-					const struct btf *btf,
+					const struct bpf_reg_state *reg,
-					const struct btf_type *t, int off,
+					int off, int size, enum bpf_access_type atype,
-					int size, enum bpf_access_type atype,
+					u32 *next_btf_id, enum bpf_type_flag *flag)
-					u32 *next_btf_id,
-					enum bpf_type_flag *flag)
 {
 	int ret = -EACCES;
 
 	if (atype == BPF_READ)
-		return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+		return btf_struct_access(log, reg, off, size, atype, next_btf_id, flag);
-					 flag);
 
 	mutex_lock(&nf_conn_btf_access_lock);
 	if (nfct_btf_struct_access)
-		ret = nfct_btf_struct_access(log, btf, t, off, size, atype, next_btf_id, flag);
+		ret = nfct_btf_struct_access(log, reg, off, size, atype, next_btf_id, flag);
 	mutex_unlock(&nf_conn_btf_access_lock);
 
 	return ret;
@@ -8738,21 +8735,18 @@ void bpf_warn_invalid_xdp_action(struct net_device *dev, struct bpf_prog *prog,
 EXPORT_SYMBOL_GPL(bpf_warn_invalid_xdp_action);
 
 static int xdp_btf_struct_access(struct bpf_verifier_log *log,
-				 const struct btf *btf,
+				 const struct bpf_reg_state *reg,
-				 const struct btf_type *t, int off,
+				 int off, int size, enum bpf_access_type atype,
-				 int size, enum bpf_access_type atype,
+				 u32 *next_btf_id, enum bpf_type_flag *flag)
-				 u32 *next_btf_id,
-				 enum bpf_type_flag *flag)
 {
 	int ret = -EACCES;
 
 	if (atype == BPF_READ)
-		return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+		return btf_struct_access(log, reg, off, size, atype, next_btf_id, flag);
-					 flag);
 
 	mutex_lock(&nf_conn_btf_access_lock);
 	if (nfct_btf_struct_access)
-		ret = nfct_btf_struct_access(log, btf, t, off, size, atype, next_btf_id, flag);
+		ret = nfct_btf_struct_access(log, reg, off, size, atype, next_btf_id, flag);
 	mutex_unlock(&nf_conn_btf_access_lock);
 
 	return ret;

net/ipv4/bpf_tcp_ca.c

@@ -69,18 +69,17 @@ static bool bpf_tcp_ca_is_valid_access(int off, int size,
 }
 
 static int bpf_tcp_ca_btf_struct_access(struct bpf_verifier_log *log,
-					const struct btf *btf,
+					const struct bpf_reg_state *reg,
-					const struct btf_type *t, int off,
+					int off, int size, enum bpf_access_type atype,
-					int size, enum bpf_access_type atype,
+					u32 *next_btf_id, enum bpf_type_flag *flag)
-					u32 *next_btf_id,
-					enum bpf_type_flag *flag)
 {
+	const struct btf_type *t;
 	size_t end;
 
 	if (atype == BPF_READ)
-		return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+		return btf_struct_access(log, reg, off, size, atype, next_btf_id, flag);
-					 flag);
 
+	t = btf_type_by_id(reg->btf, reg->btf_id);
 	if (t != tcp_sock_type) {
 		bpf_log(log, "only read is supported\n");
 		return -EACCES;

net/netfilter/nf_conntrack_bpf.c

@@ -191,19 +191,16 @@ BTF_ID(struct, nf_conn___init)
 
 /* Check writes into `struct nf_conn` */
 static int _nf_conntrack_btf_struct_access(struct bpf_verifier_log *log,
-					   const struct btf *btf,
+					   const struct bpf_reg_state *reg,
-					   const struct btf_type *t, int off,
+					   int off, int size, enum bpf_access_type atype,
-					   int size, enum bpf_access_type atype,
+					   u32 *next_btf_id, enum bpf_type_flag *flag)
-					   u32 *next_btf_id,
-					   enum bpf_type_flag *flag)
 {
-	const struct btf_type *ncit;
+	const struct btf_type *ncit, *nct, *t;
-	const struct btf_type *nct;
 	size_t end;
 
-	ncit = btf_type_by_id(btf, btf_nf_conn_ids[1]);
+	ncit = btf_type_by_id(reg->btf, btf_nf_conn_ids[1]);
-	nct = btf_type_by_id(btf, btf_nf_conn_ids[0]);
+	nct = btf_type_by_id(reg->btf, btf_nf_conn_ids[0]);
-
+	t = btf_type_by_id(reg->btf, reg->btf_id);
 	if (t != nct && t != ncit) {
 		bpf_log(log, "only read is supported\n");
 		return -EACCES;