This patch introduces hash chain support for signature verification of arbitrary bpf map objects which was described here: https://lore.kernel.org/linux-security-module/20250721211958.1881379-1-kpsingh@xxxxxxxxxx/ The UAPI is extended to allow for in-kernel checking of maps passed in via the fd_array. A hash chain is constructed from the maps, in order specified by the signature_maps field. The hash chain is terminated with the hash of the program itself. Signed-off-by: Blaise Boscaccy <bboscaccy@xxxxxxxxxxxxxxxxxxx> --- include/uapi/linux/bpf.h | 6 +++ kernel/bpf/syscall.c | 75 ++++++++++++++++++++++++++++++++-- tools/include/uapi/linux/bpf.h | 6 +++ 3 files changed, 83 insertions(+), 4 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index b42c3740e053e..c83f2a34674fd 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -1617,6 +1617,12 @@ union bpf_attr { * verification. */ __u32 keyring_id; + /* Pointer to a buffer containing the maps used in the signature + * hash chain of the BPF program. + */ + __aligned_u64 signature_maps; + /* Size of the signature maps buffer. */ + __u32 signature_maps_size; }; struct { /* anonymous struct used by BPF_OBJ_* commands */ diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 10fd3ea5d91fd..f7e9bcabd9dcc 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -2780,15 +2780,36 @@ static bool is_perfmon_prog_type(enum bpf_prog_type prog_type) } } +static inline int bpf_map_get_hash(int map_fd, void *buffer) +{ + struct bpf_map *map; + + CLASS(fd, f)(map_fd); + map = __bpf_map_get(f); + if (IS_ERR(map)) + return PTR_ERR(map); + + if (!map->ops->map_get_hash) + return -EINVAL; + + return map->ops->map_get_hash(map, SHA256_DIGEST_SIZE, buffer); +} + static noinline int bpf_prog_verify_signature(struct bpf_prog *prog, union bpf_attr *attr, bool is_kernel) { bpfptr_t usig = make_bpfptr(attr->signature, is_kernel); - struct bpf_dynptr_kern sig_ptr, insns_ptr; + bpfptr_t umaps; + struct bpf_dynptr_kern sig_ptr, insns_ptr, hash_ptr; struct bpf_key *key = NULL; void *sig; + int *maps; + int map_fd; int err = 0; + u64 buffer[8]; + u64 hash[4]; + int n; if (system_keyring_id_check(attr->keyring_id) == 0) key = bpf_lookup_system_key(attr->keyring_id); @@ -2808,16 +2829,62 @@ static noinline int bpf_prog_verify_signature(struct bpf_prog *prog, bpf_dynptr_init(&insns_ptr, prog->insnsi, BPF_DYNPTR_TYPE_LOCAL, 0, prog->len * sizeof(struct bpf_insn)); - err = bpf_verify_pkcs7_signature((struct bpf_dynptr *)&insns_ptr, - (struct bpf_dynptr *)&sig_ptr, key); + if (!attr->signature_maps_size) { + err = bpf_verify_pkcs7_signature((struct bpf_dynptr *)&insns_ptr, + (struct bpf_dynptr *)&sig_ptr, key); + } else { + bpf_dynptr_init(&hash_ptr, hash, BPF_DYNPTR_TYPE_LOCAL, 0, + sizeof(hash)); + umaps = make_bpfptr(attr->signature_maps, is_kernel); + maps = kvmemdup_bpfptr(umaps, attr->signature_maps_size * sizeof(*maps)); + if (!maps) { + err = -ENOMEM; + goto out; + } + n = attr->signature_maps_size - 1; + err = copy_from_bpfptr_offset(&map_fd, make_bpfptr(attr->fd_array, is_kernel), + maps[n] * sizeof(map_fd), + sizeof(map_fd)); + if (err < 0) + goto free_maps; + + err = bpf_map_get_hash(map_fd, hash); + if (err != 0) + goto free_maps; + + n--; + while (n >= 0) { + memcpy(buffer, hash, sizeof(hash)); + err = copy_from_bpfptr_offset(&map_fd, + make_bpfptr(attr->fd_array, is_kernel), + maps[n] * sizeof(map_fd), + sizeof(map_fd)); + if (err < 0) + goto free_maps; + + err = bpf_map_get_hash(map_fd, buffer+4); + if (err != 0) + goto free_maps; + sha256((u8 *)buffer, sizeof(buffer), (u8 *)&hash); + n--; + } + sha256((u8 *)prog->insnsi, prog->len * sizeof(struct bpf_insn), (u8 *)&buffer); + memcpy(buffer+4, hash, sizeof(hash)); + sha256((u8 *)buffer, sizeof(buffer), (u8 *)&hash); + err = bpf_verify_pkcs7_signature((struct bpf_dynptr *)&hash_ptr, + (struct bpf_dynptr *)&sig_ptr, key); +free_maps: + kvfree(maps); + } +out: bpf_key_put(key); kvfree(sig); return err; } /* last field in 'union bpf_attr' used by this command */ -#define BPF_PROG_LOAD_LAST_FIELD keyring_id +#define BPF_PROG_LOAD_LAST_FIELD signature_maps_size static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size) { diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index b42c3740e053e..c83f2a34674fd 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -1617,6 +1617,12 @@ union bpf_attr { * verification. */ __u32 keyring_id; + /* Pointer to a buffer containing the maps used in the signature + * hash chain of the BPF program. + */ + __aligned_u64 signature_maps; + /* Size of the signature maps buffer. */ + __u32 signature_maps_size; }; struct { /* anonymous struct used by BPF_OBJ_* commands */ -- 2.48.1
