bpf: Add fd_array_cnt attribute for prog_load

The fd_array attribute of the BPF_PROG_LOAD syscall may contain a set
of file descriptors: maps or btfs. This field was introduced as a
sparse array. Introduce a new attribute, fd_array_cnt, which, if
present, indicates that the fd_array is a continuous array of the
corresponding length.

If fd_array_cnt is non-zero, then every map in the fd_array will be
bound to the program, as if it was used by the program. This
functionality is similar to the BPF_PROG_BIND_MAP syscall, but such
maps can be used by the verifier during the program load.

Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241213130934.1087929-5-aspsk@isovalent.com

include/uapi/linux/bpf.h

@@ -1573,6 +1573,16 @@ union bpf_attr {
 		 * If provided, prog_flags should have BPF_F_TOKEN_FD flag set.
 		 */
 		__s32		prog_token_fd;
+		/* The fd_array_cnt can be used to pass the length of the
+		 * fd_array array. In this case all the [map] file descriptors
+		 * passed in this array will be bound to the program, even if
+		 * the maps are not referenced directly. The functionality is
+		 * similar to the BPF_PROG_BIND_MAP syscall, but maps can be
+		 * used by the verifier during the program load. If provided,
+		 * then the fd_array[0,...,fd_array_cnt-1] is expected to be
+		 * continuous.
+		 */
+		__u32		fd_array_cnt;
 	};
 
 	struct { /* anonymous struct used by BPF_OBJ_* commands */

kernel/bpf/syscall.c

@@ -2730,7 +2730,7 @@ static bool is_perfmon_prog_type(enum bpf_prog_type prog_type)
 }
 
 /* last field in 'union bpf_attr' used by this command */
-#define BPF_PROG_LOAD_LAST_FIELD prog_token_fd
+#define BPF_PROG_LOAD_LAST_FIELD fd_array_cnt
 
 static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
 {

kernel/bpf/verifier.c

@@ -19505,22 +19505,10 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 	return 0;
 }
 
-/* Add map behind fd to used maps list, if it's not already there, and return
- * its index.
- * Returns <0 on error, or >= 0 index, on success.
- */
-static int add_used_map_from_fd(struct bpf_verifier_env *env, int fd)
+static int __add_used_map(struct bpf_verifier_env *env, struct bpf_map *map)
 {
-	CLASS(fd, f)(fd);
-	struct bpf_map *map;
 	int i, err;
 
-	map = __bpf_map_get(f);
-	if (IS_ERR(map)) {
-		verbose(env, "fd %d is not pointing to valid bpf_map\n", fd);
-		return PTR_ERR(map);
-	}
-
 	/* check whether we recorded this map already */
 	for (i = 0; i < env->used_map_cnt; i++)
 		if (env->used_maps[i] == map)
@@ -19551,6 +19539,24 @@ static int add_used_map_from_fd(struct bpf_verifier_env *env, int fd)
 	return env->used_map_cnt - 1;
 }
 
+/* Add map behind fd to used maps list, if it's not already there, and return
+ * its index.
+ * Returns <0 on error, or >= 0 index, on success.
+ */
+static int add_used_map(struct bpf_verifier_env *env, int fd)
+{
+	struct bpf_map *map;
+	CLASS(fd, f)(fd);
+
+	map = __bpf_map_get(f);
+	if (IS_ERR(map)) {
+		verbose(env, "fd %d is not pointing to valid bpf_map\n", fd);
+		return PTR_ERR(map);
+	}
+
+	return __add_used_map(env, map);
+}
+
 /* find and rewrite pseudo imm in ld_imm64 instructions:
  *
  * 1. if it accesses map FD, replace it with actual map pointer.
@@ -19642,7 +19648,7 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
 				break;
 			}
 
-			map_idx = add_used_map_from_fd(env, fd);
+			map_idx = add_used_map(env, fd);
 			if (map_idx < 0)
 				return map_idx;
 			map = env->used_maps[map_idx];
@@ -22850,6 +22856,73 @@ struct btf *bpf_get_btf_vmlinux(void)
 	return btf_vmlinux;
 }
 
+/*
+ * The add_fd_from_fd_array() is executed only if fd_array_cnt is non-zero. In
+ * this case expect that every file descriptor in the array is either a map or
+ * a BTF. Everything else is considered to be trash.
+ */
+static int add_fd_from_fd_array(struct bpf_verifier_env *env, int fd)
+{
+	struct bpf_map *map;
+	struct btf *btf;
+	CLASS(fd, f)(fd);
+	int err;
+
+	map = __bpf_map_get(f);
+	if (!IS_ERR(map)) {
+		err = __add_used_map(env, map);
+		if (err < 0)
+			return err;
+		return 0;
+	}
+
+	btf = __btf_get_by_fd(f);
+	if (!IS_ERR(btf)) {
+		err = __add_used_btf(env, btf);
+		if (err < 0)
+			return err;
+		return 0;
+	}
+
+	verbose(env, "fd %d is not pointing to valid bpf_map or btf\n", fd);
+	return PTR_ERR(map);
+}
+
+static int process_fd_array(struct bpf_verifier_env *env, union bpf_attr *attr, bpfptr_t uattr)
+{
+	size_t size = sizeof(int);
+	int ret;
+	int fd;
+	u32 i;
+
+	env->fd_array = make_bpfptr(attr->fd_array, uattr.is_kernel);
+
+	/*
+	 * The only difference between old (no fd_array_cnt is given) and new
+	 * APIs is that in the latter case the fd_array is expected to be
+	 * continuous and is scanned for map fds right away
+	 */
+	if (!attr->fd_array_cnt)
+		return 0;
+
+	/* Check for integer overflow */
+	if (attr->fd_array_cnt >= (U32_MAX / size)) {
+		verbose(env, "fd_array_cnt is too big (%u)\n", attr->fd_array_cnt);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < attr->fd_array_cnt; i++) {
+		if (copy_from_bpfptr_offset(&fd, env->fd_array, i * size, size))
+			return -EFAULT;
+
+		ret = add_fd_from_fd_array(env, fd);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
 int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u32 uattr_size)
 {
 	u64 start_time = ktime_get_ns();
@@ -22881,7 +22954,6 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
 		env->insn_aux_data[i].orig_idx = i;
 	env->prog = *prog;
 	env->ops = bpf_verifier_ops[env->prog->type];
-	env->fd_array = make_bpfptr(attr->fd_array, uattr.is_kernel);
 
 	env->allow_ptr_leaks = bpf_allow_ptr_leaks(env->prog->aux->token);
 	env->allow_uninit_stack = bpf_allow_uninit_stack(env->prog->aux->token);
@@ -22904,6 +22976,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
 	if (ret)
 		goto err_unlock;
 
+	ret = process_fd_array(env, attr, uattr);
+	if (ret)
+		goto skip_full_check;
+
 	mark_verifier_state_clean(env);
 
 	if (IS_ERR(btf_vmlinux)) {

tools/include/uapi/linux/bpf.h

@@ -1573,6 +1573,16 @@ union bpf_attr {
 		 * If provided, prog_flags should have BPF_F_TOKEN_FD flag set.
 		 */
 		__s32		prog_token_fd;
+		/* The fd_array_cnt can be used to pass the length of the
+		 * fd_array array. In this case all the [map] file descriptors
+		 * passed in this array will be bound to the program, even if
+		 * the maps are not referenced directly. The functionality is
+		 * similar to the BPF_PROG_BIND_MAP syscall, but maps can be
+		 * used by the verifier during the program load. If provided,
+		 * then the fd_array[0,...,fd_array_cnt-1] is expected to be
+		 * continuous.
+		 */
+		__u32		fd_array_cnt;
 	};
 
 	struct { /* anonymous struct used by BPF_OBJ_* commands */