bpf: Add BPF token support to BPF_MAP_CREATE command

Allow providing token_fd for BPF_MAP_CREATE command to allow controlled
BPF map creation from unprivileged process through delegated BPF token.
New BPF_F_TOKEN_FD flag is added to specify together with BPF token FD
for BPF_MAP_CREATE command.

Wire through a set of allowed BPF map types to BPF token, derived from
BPF FS at BPF token creation time. This, in combination with allowed_cmds
allows to create a narrowly-focused BPF token (controlled by privileged
agent) with a restrictive set of BPF maps that application can attempt
to create.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20240124022127.2379740-5-andrii@kernel.org

include/uapi/linux/bpf.h

@@ -983,6 +983,7 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_BLOOM_FILTER,
 	BPF_MAP_TYPE_USER_RINGBUF,
 	BPF_MAP_TYPE_CGRP_STORAGE,
+	__MAX_BPF_MAP_TYPE
 };
 
 /* Note that tracing related programs such as
@@ -1365,6 +1366,9 @@ enum {
 
 /* Flag for value_type_btf_obj_fd, the fd is available */
 	BPF_F_VTYPE_BTF_OBJ_FD	= (1U << 15),
+
+/* BPF token FD is passed in a corresponding command's token_fd field */
+	BPF_F_TOKEN_FD          = (1U << 16),
 };
 
 /* Flags for BPF_PROG_QUERY. */
@@ -1443,6 +1447,10 @@ union bpf_attr {
 						 * type data for
 						 * btf_vmlinux_value_type_id.
 						 */
+		/* BPF token FD to use with BPF_MAP_CREATE operation.
+		 * If provided, map_flags should have BPF_F_TOKEN_FD flag set.
+		 */
+		__s32	map_token_fd;
 	};
 
 	struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */