[PATCH bpf-next v4 0/9] Verify BPF signed loader at load time

[PATCH bpf-next v4 0/9] Verify BPF signed loader at load time

[Daniel Borkmann]

The BPF signing scheme signs a light skeleton's loader program and lets
the loader vouch for everything else: bpftool bakes the SHA256 of the
metadata map into the loader's instructions, signs the instructions, and
the loader compares the (frozen, exclusive) map against that hash from
within BPF once it runs. The construction is sound as a trusted hash
chain, but the kernel itself never attests the metadata, and that split
has been the recurring objection from the LSM / integrity side since the
scheme was proposed.

This proposal closes both gaps by having the kernel verify the metadata
at BPF_PROG_LOAD time, before the LSM admission hook and before the
verifier, /without/ growing the UAPI. A signed loader binds its metadata
map(s) through the existing fd_array/fd_array_cnt, and exclusive maps
are already bound to the loader's digest via excl_prog_hash. When a
signature is present, the kernel collects the exclusive maps from the
fd_array and appends their frozen contents to the instructions before
PKCS#7 verification, so the signature covers ...

    insns || metadata_0 || metadata_1 || [...]

... in fd_array order. The in-loader hash check is dropped from the
gen_loader entirely: generated loaders carry no verification logic
anymore, and signing or verifying a skeleton becomes an ordinary CMS
operation over bytes that sit verbatim in the skeleton, reproducible
offline. A signed program is either BPF_SIG_UNSIGNED or BPF_SIG_VERIFIED
with nothing in between.

There is no new UAPI, we now have a single signature scheme, no LSM
code reaching into BPF internals, no new LSM hook, and unsigned loads
are completely unaffected. It is also less complex since the loader
does not need to deal with BTF, an extra kfunc, etc, as proposed in
an earlier series [0]. Tested against full BPF CI which came back
green. For more details and examples, see the documentation patch in
this series.

  [0] https://lore.kernel.org/bpf/20260522023234.3778588-1-kpsingh@kernel.org/

v3 -> v4:
  - Fix upper limit in MAX_FD_ARRAY_CNT (Anton)
  - Reject !fd_array && attr->fd_array_cnt (Anton)
  - Add bpftool patch wrt ignored return value of EVP_Digest() (sashiko)
  - Fix setting of gen_loader_fixture_init (sashiko)
  - Fix unused map_fd cleanup branch in selftest (bot+bpf-ci)
  - Remove now unused map->excl member and adjust selftests
  - Added more BPF signed_loader corner case selftest coverage
  - Added Paul's Nack wrt bpf_prog_load LSM hook dispute
  - Added patch 2 to move bigger allocations below fd_array
    resolution (Paul)
v2 -> v3:
  - Added first commit to cache and work on objects in fd_array
    which was the most recent issue sashiko rightfully complained
  - Added more BPF signed_loader selftest coverage to cover that
    usage of sparse fd_array or map fds gets rejected
  - I left the security_bpf_prog_load as in v2 given preference
    from BPF side over adding new hook
v1 -> v2:
  - Addressed both sashiko complaints, the TOCTOU bug regarding
    fd_array processing, as well as exclusive map checking to
    only allow array maps. The validation is now moved into the
    verifier before the main verification work happens. This also
    gives the opportunity to utilize the verifier log.

Daniel Borkmann (9):
  bpf: Resolve and cache fd_array objects at load time
  bpf: Move bigger allocations below fd_array resolution
  bpf: Verify signed loader metadata at load time
  libbpf: Drop in-loader metadata check for load-time verification
  bpftool: Check EVP_Digest when computing excl_prog_hash
  bpftool: Cover loader metadata with the program signature
  selftests/bpf: Adjust bpf_map layout in verifier_map_ptr
  selftests/bpf: Verify load-time signed loader metadata
  Documentation/bpf: Add BPF signing and enforcement doc

 Documentation/bpf/index.rst                   |    1 +
 Documentation/bpf/signing.rst                 |  496 ++++++++
 include/linux/bpf.h                           |    1 -
 include/linux/bpf_verifier.h                  |   23 +-
 kernel/bpf/syscall.c                          |   83 +-
 kernel/bpf/verifier.c                         |  450 ++++++--
 tools/bpf/bpftool/gen.c                       |    2 +
 tools/bpf/bpftool/sign.c                      |   24 +-
 tools/lib/bpf/bpf_gen_internal.h              |    1 -
 tools/lib/bpf/gen_loader.c                    |   76 +-
 tools/lib/bpf/libbpf_internal.h               |    1 -
 tools/lib/bpf/skel_internal.h                 |   31 +-
 .../selftests/bpf/prog_tests/signed_loader.c  | 1004 ++++++++++++++---
 .../selftests/bpf/progs/test_signed_loader.c  |    9 +-
 .../selftests/bpf/progs/verifier_map_ptr.c    |   23 +-
 15 files changed, 1786 insertions(+), 439 deletions(-)
 create mode 100644 Documentation/bpf/signing.rst

-- 
2.43.0

[PATCH bpf-next v4 1/9] bpf: Resolve and cache fd_array objects at load time

[Daniel Borkmann]

The fd_array passed to BPF_PROG_LOAD carries the map and module BTF file
descriptors a program binds. The verifier reads it more than once during
a load: process_fd_array() walks it to bind the maps and BTFs, and
check_and_resolve_insns() and the kfunc BTF resolver later read it again
to resolve the program's BPF_PSEUDO_MAP_IDX* and module kfunc refs.

For signed BPF, we need these upfront in memory, thus resolve each fd to
its object once and cache it by fd_array index, then bind that cached
object for the rest of the load. env->fd_array becomes a small per-slot
{map, btf} cache rather than a bpfptr_t; every later reference is then
an in-bounds lookup of an already-resolved object, and an index outside
the cache is rejected instead of read from user memory:

  - continuous (fd_array_cnt given): the caller declares the length and
    every entry is resolved and bound up front (used also by the BPF
    signed loader)

  - sparse (no fd_array_cnt): left as the legacy path with no fd_array
    cache; each reference reads its fd from the caller's fd_array and
    resolves it on the spot. Deduplication in used_maps and the kfunc BTF
    table keeps this correct, and only unsigned programs use this shape.

Split these into separate helpers to make it easier to follow.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Anton Protopopov <a.s.protopopov@gmail.com>
---
 include/linux/bpf_verifier.h |  22 +++-
 kernel/bpf/verifier.c        | 223 +++++++++++++++++++++++++++--------
 2 files changed, 193 insertions(+), 52 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 76b8b7627a10..bb57773cde37 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -898,6 +898,14 @@ struct bpf_scc_info {
 
 struct bpf_liveness;
 
+struct bpf_fd_array {
+	union {
+		struct bpf_map *map;
+		struct btf *btf;
+		unsigned long val;
+	};
+};
+
 /* single container for all structs
  * one verifier_env per bpf_check() call
  */
@@ -989,7 +997,19 @@ struct bpf_verifier_env {
 	u32 free_list_size;
 	u32 explored_states_size;
 	u32 num_backedges;
-	bpfptr_t fd_array;
+	/*
+	 * The program's fd_array comes in two shapes, told apart by whether
+	 * the caller passed fd_array_cnt. They are mutually exclusive:
+	 *  - continuous (fd_array_cnt given): ->fd_array holds every entry
+	 *    resolved to its object up front, indexed by fd_array position,
+	 *    with ->fd_array_cnt slots; ->fd_array_raw is unused.
+	 *  - sparse (no fd_array_cnt): ->fd_array is NULL, and entries are
+	 *    read from ->fd_array_raw (the caller's fd_array) and resolved
+	 *    on the spot at each reference.
+	 */
+	struct bpf_fd_array *fd_array;
+	u32 fd_array_cnt;
+	bpfptr_t fd_array_raw;
 
 	/* bit mask to keep track of whether a register has been accessed
 	 * since the last time the function state was printed
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d46f7db20d8f..33f9c47ee197 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2490,6 +2490,79 @@ int bpf_get_kfunc_addr(const struct bpf_prog *prog, u32 func_id,
 	return 0;
 }
 
+#define BPF_FD_SLOT_BTF	1UL
+
+static void fd_slot_set_map(struct bpf_fd_array *slot, struct bpf_map *map)
+{
+	slot->val = (unsigned long)map;
+}
+
+static void fd_slot_set_btf(struct bpf_fd_array *slot, struct btf *btf)
+{
+	slot->val = (unsigned long)btf | BPF_FD_SLOT_BTF;
+}
+
+static struct bpf_map *fd_slot_map(struct bpf_fd_array slot)
+{
+	if (slot.val & BPF_FD_SLOT_BTF)
+		return NULL;
+	return (struct bpf_map *)slot.val;
+}
+
+static struct btf *fd_slot_btf(struct bpf_fd_array slot)
+{
+	if (!(slot.val & BPF_FD_SLOT_BTF))
+		return NULL;
+	return (struct btf *)(slot.val & ~BPF_FD_SLOT_BTF);
+}
+
+static struct btf *
+fd_array_get_btf_continuous(struct bpf_verifier_env *env, u32 idx)
+{
+	struct btf *btf;
+
+	if (idx >= env->fd_array_cnt) {
+		verbose(env, "kfunc fd_idx %u out of bounds, fd_array_cnt %u\n",
+			idx, env->fd_array_cnt);
+		return ERR_PTR(-EINVAL);
+	}
+	btf = fd_slot_btf(env->fd_array[idx]);
+	if (!btf) {
+		verbose(env, "kfunc fd_idx %u is not a module BTF\n", idx);
+		return ERR_PTR(-EINVAL);
+	}
+	btf_get(btf);
+	return btf;
+}
+
+static struct btf *
+fd_array_get_btf_sparse(struct bpf_verifier_env *env, u32 idx)
+{
+	struct btf *btf;
+	int btf_fd;
+
+	if (copy_from_bpfptr_offset(&btf_fd, env->fd_array_raw,
+				    (size_t)idx * sizeof(btf_fd), sizeof(btf_fd)))
+		return ERR_PTR(-EFAULT);
+	btf = btf_get_by_fd(btf_fd);
+	if (IS_ERR(btf)) {
+		verbose(env, "invalid module BTF fd specified\n");
+		return btf;
+	}
+	return btf;
+}
+
+static struct btf *fd_array_get_btf(struct bpf_verifier_env *env, u32 idx)
+{
+	if (env->fd_array)
+		return fd_array_get_btf_continuous(env, idx);
+	if (!bpfptr_is_null(env->fd_array_raw))
+		return fd_array_get_btf_sparse(env, idx);
+
+	verbose(env, "kfunc offset > 0 without fd_array is invalid\n");
+	return ERR_PTR(-EPROTO);
+}
+
 static struct btf *__find_kfunc_desc_btf(struct bpf_verifier_env *env,
 					 s16 offset)
 {
@@ -2498,7 +2571,6 @@ static struct btf *__find_kfunc_desc_btf(struct bpf_verifier_env *env,
 	struct bpf_kfunc_btf *b;
 	struct module *mod;
 	struct btf *btf;
-	int btf_fd;
 
 	tab = env->prog->aux->kfunc_btf_tab;
 	b = bsearch(&kf_btf, tab->descs, tab->nr_descs,
@@ -2509,22 +2581,9 @@ static struct btf *__find_kfunc_desc_btf(struct bpf_verifier_env *env,
 			return ERR_PTR(-E2BIG);
 		}
 
-		if (bpfptr_is_null(env->fd_array)) {
-			verbose(env, "kfunc offset > 0 without fd_array is invalid\n");
-			return ERR_PTR(-EPROTO);
-		}
-
-		if (copy_from_bpfptr_offset(&btf_fd, env->fd_array,
-					    offset * sizeof(btf_fd),
-					    sizeof(btf_fd)))
-			return ERR_PTR(-EFAULT);
-
-		btf = btf_get_by_fd(btf_fd);
-		if (IS_ERR(btf)) {
-			verbose(env, "invalid module BTF fd specified\n");
+		btf = fd_array_get_btf(env, offset);
+		if (IS_ERR(btf))
 			return btf;
-		}
-
 		if (!btf_is_module(btf)) {
 			verbose(env, "BTF fd for kfunc is not a module BTF\n");
 			btf_put(btf);
@@ -17923,6 +17982,44 @@ static int add_used_map(struct bpf_verifier_env *env, int fd)
 	return __add_used_map(env, map);
 }
 
+static int fd_array_get_map_idx_continuous(struct bpf_verifier_env *env, u32 idx)
+{
+	struct bpf_map *map;
+
+	if (idx >= env->fd_array_cnt) {
+		verbose(env, "fd_idx %u out of bounds, fd_array_cnt %u\n",
+			idx, env->fd_array_cnt);
+		return -EINVAL;
+	}
+	map = fd_slot_map(env->fd_array[idx]);
+	if (!map) {
+		verbose(env, "fd_idx %u is not a map\n", idx);
+		return -EINVAL;
+	}
+	return __add_used_map(env, map);
+}
+
+static int fd_array_get_map_idx_sparse(struct bpf_verifier_env *env, u32 idx)
+{
+	int fd;
+
+	if (copy_from_bpfptr_offset(&fd, env->fd_array_raw,
+				    (size_t)idx * sizeof(fd), sizeof(fd)))
+		return -EFAULT;
+	return add_used_map(env, fd);
+}
+
+static int fd_array_get_map_idx(struct bpf_verifier_env *env, u32 idx)
+{
+	if (env->fd_array)
+		return fd_array_get_map_idx_continuous(env, idx);
+	if (!bpfptr_is_null(env->fd_array_raw))
+		return fd_array_get_map_idx_sparse(env, idx);
+
+	verbose(env, "fd_idx without fd_array is invalid\n");
+	return -EPROTO;
+}
+
 static int check_alu_fields(struct bpf_verifier_env *env, struct bpf_insn *insn)
 {
 	u8 class = BPF_CLASS(insn->code);
@@ -18140,7 +18237,6 @@ static int check_and_resolve_insns(struct bpf_verifier_env *env)
 			struct bpf_map *map;
 			int map_idx;
 			u64 addr;
-			u32 fd;
 
 			if (i == insn_cnt - 1 || insn[1].code != 0 ||
 			    insn[1].dst_reg != 0 || insn[1].src_reg != 0 ||
@@ -18192,21 +18288,13 @@ static int check_and_resolve_insns(struct bpf_verifier_env *env)
 			switch (insn[0].src_reg) {
 			case BPF_PSEUDO_MAP_IDX_VALUE:
 			case BPF_PSEUDO_MAP_IDX:
-				if (bpfptr_is_null(env->fd_array)) {
-					verbose(env, "fd_idx without fd_array is invalid\n");
-					return -EPROTO;
-				}
-				if (copy_from_bpfptr_offset(&fd, env->fd_array,
-							    insn[0].imm * sizeof(fd),
-							    sizeof(fd)))
-					return -EFAULT;
+				map_idx = fd_array_get_map_idx(env, insn[0].imm);
 				break;
 			default:
-				fd = insn[0].imm;
+				map_idx = add_used_map(env, insn[0].imm);
 				break;
 			}
 
-			map_idx = add_used_map(env, fd);
 			if (map_idx < 0)
 				return map_idx;
 			map = env->used_maps[map_idx];
@@ -19481,7 +19569,7 @@ struct btf *bpf_get_btf_vmlinux(void)
  * 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)
+static int add_fd_from_fd_array(struct bpf_verifier_env *env, u32 idx, int fd)
 {
 	struct bpf_map *map;
 	struct btf *btf;
@@ -19493,51 +19581,83 @@ static int add_fd_from_fd_array(struct bpf_verifier_env *env, int fd)
 		err = __add_used_map(env, map);
 		if (err < 0)
 			return err;
+		fd_slot_set_map(&env->fd_array[idx], map);
 		return 0;
 	}
 
 	btf = __btf_get_by_fd(f);
 	if (!IS_ERR(btf)) {
 		btf_get(btf);
-		return __add_used_btf(env, btf);
+		err = __add_used_btf(env, btf);
+		if (err < 0)
+			return err;
+		fd_slot_set_btf(&env->fd_array[idx], btf);
+		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)
+/*
+ * A continuous fd_array is resolved into an in-memory cache with one slot
+ * per entry. The bound here is deliberately generous and not derived from
+ * the per-program object limits: Duplicate entries /are/ permitted, and
+ * the number of distinct maps and BTFs a program can bind is enforced when
+ * each entry is resolved by __add_used_map() and __add_used_btf().
+ */
+#define MAX_FD_ARRAY_CNT 4096
+
+static int process_fd_array_continuous(struct bpf_verifier_env *env,
+				       bpfptr_t fd_array, u32 cnt)
 {
-	size_t size = sizeof(int);
-	int ret;
-	int fd;
+	int fd, ret;
 	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;
+	if (cnt > MAX_FD_ARRAY_CNT) {
+		verbose(env, "fd_array has too many entries (%u, max %u)\n",
+			cnt, MAX_FD_ARRAY_CNT);
+		return -E2BIG;
 	}
 
-	for (i = 0; i < attr->fd_array_cnt; i++) {
-		if (copy_from_bpfptr_offset(&fd, env->fd_array, i * size, size))
+	env->fd_array = kvcalloc(cnt, sizeof(*env->fd_array),
+				 GFP_KERNEL_ACCOUNT);
+	if (!env->fd_array)
+		return -ENOMEM;
+	env->fd_array_cnt = cnt;
+	for (i = 0; i < cnt; i++) {
+		if (copy_from_bpfptr_offset(&fd, fd_array,
+					    (size_t)i * sizeof(fd), sizeof(fd)))
 			return -EFAULT;
-
-		ret = add_fd_from_fd_array(env, fd);
+		ret = add_fd_from_fd_array(env, i, fd);
 		if (ret)
 			return ret;
 	}
+	return 0;
+}
 
+static int process_fd_array(struct bpf_verifier_env *env,
+			    union bpf_attr *attr, bpfptr_t uattr)
+{
+	bpfptr_t fd_array = make_bpfptr(attr->fd_array, uattr.is_kernel);
+
+	if (bpfptr_is_null(fd_array)) {
+		if (attr->fd_array_cnt) {
+			verbose(env, "fd_array_cnt %u without fd_array is invalid\n",
+				attr->fd_array_cnt);
+			return -EINVAL;
+		}
+		return 0;
+	}
+	/*
+	 * New API: the caller passes fd_array_cnt and a continuous array that
+	 * is resolved and bound up front. Legacy API (no fd_array_cnt): keep
+	 * the caller's array and resolve entries on the spot at each reference.
+	 */
+	if (attr->fd_array_cnt)
+		return process_fd_array_continuous(env, fd_array,
+						   attr->fd_array_cnt);
+	env->fd_array_raw = fd_array;
 	return 0;
 }
 
@@ -20038,6 +20158,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 		mutex_unlock(&bpf_verifier_lock);
 	bpf_clear_insn_aux_data(env, 0, env->prog->len);
 err_free_env:
+	kvfree(env->fd_array);
 	bpf_stack_liveness_free(env);
 	kvfree(env->cfg.insn_postorder);
 	kvfree(env->scc_info);
-- 
2.43.0

[PATCH bpf-next v4 2/9] bpf: Move bigger allocations below fd_array resolution

[Daniel Borkmann]

Reorder the preparation work in bpf_check() such that only the minimally
necessary setup happens up front: allocating the env, initializing the
verifier log and resolving the fd_array that a signed BPF metadata map
needs.

The worst case allocation (until hitting the security_bpf_prog_load()
admission hook once placed after fd_array) for this preparation part is
~90K which is the env itself (~54K) plus the continuous fd_array cache
(at most 32K). The insn_aux_data array is moved into a later stage in
the verification process.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/verifier.c | 52 +++++++++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 22 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 33f9c47ee197..e227c76a8dd9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19894,18 +19894,6 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 		return -ENOMEM;
 
 	env->bt.env = env;
-
-	len = (*prog)->len;
-	env->insn_aux_data =
-		vzalloc(array_size(sizeof(struct bpf_insn_aux_data), len));
-	ret = -ENOMEM;
-	if (!env->insn_aux_data)
-		goto err_free_env;
-	for (i = 0; i < len; i++)
-		env->insn_aux_data[i].orig_idx = i;
-	env->succ = bpf_iarray_realloc(NULL, 2);
-	if (!env->succ)
-		goto err_free_env;
 	env->prog = *prog;
 	env->ops = bpf_verifier_ops[env->prog->type];
 
@@ -19915,21 +19903,33 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 	env->bypass_spec_v4 = bpf_bypass_spec_v4(env->prog->aux->token);
 	env->bpf_capable = is_priv = bpf_token_capable(env->prog->aux->token, CAP_BPF);
 
-	bpf_get_btf_vmlinux();
-
-	/* grab the mutex to protect few globals used by verifier */
-	if (!is_priv)
-		mutex_lock(&bpf_verifier_lock);
-
 	/* user could have requested verbose verifier output
 	 * and supplied buffer to store the verification trace
 	 */
 	ret = bpf_vlog_init(&env->log, attr_log->level, attr_log->ubuf, attr_log->size);
 	if (ret)
-		goto err_unlock;
+		goto err_free_env;
 
 	ret = process_fd_array(env, attr, uattr);
 	if (ret)
+		goto err_prep;
+
+	bpf_get_btf_vmlinux();
+
+	/* grab the mutex to protect few globals used by verifier */
+	if (!is_priv)
+		mutex_lock(&bpf_verifier_lock);
+
+	len = env->prog->len;
+	env->insn_aux_data =
+		vzalloc(array_size(sizeof(struct bpf_insn_aux_data), len));
+	ret = -ENOMEM;
+	if (!env->insn_aux_data)
+		goto skip_full_check;
+	for (i = 0; i < len; i++)
+		env->insn_aux_data[i].orig_idx = i;
+	env->succ = bpf_iarray_realloc(NULL, 2);
+	if (!env->succ)
 		goto skip_full_check;
 
 	mark_verifier_state_clean(env);
@@ -20153,18 +20153,26 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 	*prog = env->prog;
 
 	module_put(env->attach_btf_mod);
-err_unlock:
 	if (!is_priv)
 		mutex_unlock(&bpf_verifier_lock);
-	bpf_clear_insn_aux_data(env, 0, env->prog->len);
+	goto err_free_env;
+err_prep:
+	err = bpf_log_attr_finalize(attr_log, &env->log);
+	if (err)
+		ret = err;
+	release_insn_arrays(env);
+	release_maps(env);
+	release_btfs(env);
 err_free_env:
+	if (env->insn_aux_data)
+		bpf_clear_insn_aux_data(env, 0, env->prog->len);
+	vfree(env->insn_aux_data);
 	kvfree(env->fd_array);
 	bpf_stack_liveness_free(env);
 	kvfree(env->cfg.insn_postorder);
 	kvfree(env->scc_info);
 	kvfree(env->succ);
 	kvfree(env->gotox_tmp_buf);
-	vfree(env->insn_aux_data);
 	kvfree(env);
 	return ret;
 }
-- 
2.43.0

[PATCH bpf-next v4 3/9] bpf: Verify signed loader metadata at load time

[Daniel Borkmann]

A signed gen_loader program carries the programs, maps and relocations
it installs in a metadata array map. The loader instructions are covered
by the PKCS#7 signature, but the metadata map is not: Today the loader
compares the map contents from within BPF against a hash baked into its
(signed) instructions, using the kernel-cached map hash. The kernel
itself never actually attests that the metadata the loader installs is
the metadata that was signed.

This split is the core of the long-standing objection to the BPF signing
scheme from the LSM / integrity side: the integrity check of a light
skeleton only completes once the loader program runs, that is, after the
security_bpf_prog_load() hook, so at admission time an LSM observes a
program whose payload has not yet been verified. Auditing the chain
link is also not a purely cryptographic operation: whoever signs or
reviews an lskel has to disassemble the loader's preamble to convince
themselves that the embedded hash check is present and correct [0][1].
Two acceptable fixes were identified in those threads: Complete the
integrity check before the admission hook fires, or add a second hook
that collects the verification result after the loader ran [2]. Covering
both the loader and its maps directly with the PKCS#7 signature is what
Blaise Boscaccy's patchsets proposed in several forms. Let's implement
the former, without growing the UAPI, and in particular as a single
unified scheme where the signature spans the raw bytes rather than
derived hashes.

A signed loader binds its metadata map(s) through the existing fd_array,
and an exclusive map is already bound to a program digest (excl_prog_hash).
So when a signature is present, collect the exclusive maps from fd_array
and append their frozen contents to the instructions before verification:
The signature now covers insns || metadata_0 || metadata_1 || [...] in
the fd_array order, and verification completes in bpf_check(), once the
fd_array maps are resolved into used_maps, before the LSM admission hook
and the rest of verification. A program is either BPF_SIG_UNSIGNED or
BPF_SIG_VERIFIED, with nothing in between. While folding the fd_array
maps, a non-exclusive map bound to a signed program is rejected, so every
map folded into the signature is exclusive. A signed loader that fails
to cover its metadata thus does not load, and BPF_SIG_VERIFIED always
means the instructions and every exclusive map are authentic. The maps
must be frozen so the hashed bytes cannot change before the loader runs;
the map <-> program digest binding is enforced by the verifier for every
used map. Binding maps through fd_array_cnt makes the verifier resolve
and excl-check them (excl_prog_sha vs prog->digest) before it would
otherwise compute the digest, so compute prog->digest up front in
bpf_check(), over the unmodified instructions the signature covers, for
a load that folds metadata.

Unsigned programs are not affected by the signature path; for them the
LSM admission hook merely moves below fd_array resolution, with minimal
bounded work in between (see the previous commit). Note, signed loaders
generated by older libbpf/bpftool versions need to be regenerated; some
of the recent fixes we've had on the signed loader side require the
latter already to close gaps.

Finally, some remarks around the security_bpf_prog_load() placement
given there was pushback, demanding either a new hook or a reuse of
the existing security_bpf_prog() hook [3]: Just for loading a single
BPF program it would then need to pass through four layers of LSM hooks:

  1) security_bpf (cmd=PROG_LOAD): for gating various bpf subcmds
  2) security_bpf_prog_load: historical admission hook (CAP/token,
     prog_type, attach point), pre-verification
  3) security_bpf_prog_verify_signature: newly asked admission hook,
     same role as 2), plus the BPF signature verdict
  4) security_bpf_prog: gate handing the prog fd back to userspace,
     verification done & signature verified

The use-cases of 2) and 3) conflate, thus BPF community prefers to just
keep a total of 3 LSM hooks (as-is today): 3) makes 2) incoherent given
they are the /same class/ of hook, that is, access-control admission on
the load and split only by _what_ they can see. Worse, with the split,
for a signed BPF program security_bpf_prog_load 2) admits a program whose
signature has not been checked, so a policy gating at 2) is structurally
unable to express "admit only verified" and every such policy is forced
onto 3) *anyway*. In other words, one doesn't get two complementary hooks,
but rather, one real admission hook aka 3) plus a now-degraded /legacy/
hook 2) that can't answer the question operators actually want to ask.

Reusing security_bpf_prog() 4) for admission is no alternative either:
it fires only after the entire verifier (and JIT) pipeline ran, so
denying a not-yet-verified program at that point burns exactly the
work a denial is supposed to avoid, and by then the program has an id
assigned and the kallsyms/perf/audit load events fired. Policies are
free to also consume the signature verdict at 4), but admission control
belongs into security_bpf_prog_load(). Hence the latter remains the only
admission hook, merely moved past signature verification; with moving
large allocations further down into the BPF verifier, there is now only
minimal work between the old and new location.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Nacked-by: Paul Moore <paul@paul-moore.com> # (don't move bpf_prog_load LSM hook)
Link: https://lore.kernel.org/bpf/2f71d6c03698eb17d51f7247efde777627ee578a.camel@HansenPartnership.com [0]
Link: https://lore.kernel.org/lkml/ecf0521ed302db672672ebfbc670ecfba36a6e00.camel@HansenPartnership.com [1]
Link: https://lore.kernel.org/bpf/88703f00d5b7a779728451008626efa45e42db3d.camel@HansenPartnership.com [2]
Link: https://lore.kernel.org/bpf/DJOFY21DYUI4.19WKQ3NPZ4H5R@gmail.com [3]
---
 include/linux/bpf_verifier.h |   1 +
 kernel/bpf/syscall.c         |  76 +--------------
 kernel/bpf/verifier.c        | 175 +++++++++++++++++++++++++++++++++++
 3 files changed, 178 insertions(+), 74 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index bb57773cde37..317e99b9acc0 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -947,6 +947,7 @@ struct bpf_verifier_env {
 	bool bypass_spec_v4;
 	bool seen_direct_write;
 	bool seen_exception;
+	bool signature;
 	struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
 	const struct bpf_line_info *prev_linfo;
 	struct bpf_verifier_log log;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6db306d23b47..e898fad01aaf 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -40,7 +40,6 @@
 #include <linux/tracepoint.h>
 #include <linux/overflow.h>
 #include <linux/cookie.h>
-#include <linux/verification.h>
 #include <linux/btf_ids.h>
 
 #include <net/netfilter/nf_bpf_link.h>
@@ -2886,64 +2885,6 @@ static bool is_perfmon_prog_type(enum bpf_prog_type prog_type)
 	}
 }
 
-static enum bpf_sig_keyring bpf_classify_keyring(s32 keyring_id)
-{
-	switch (keyring_id) {
-	case 0:
-		return BPF_SIG_KEYRING_BUILTIN;
-	case (s32)(unsigned long)VERIFY_USE_SECONDARY_KEYRING:
-		return BPF_SIG_KEYRING_SECONDARY;
-	case (s32)(unsigned long)VERIFY_USE_PLATFORM_KEYRING:
-		return BPF_SIG_KEYRING_PLATFORM;
-	default:
-		return BPF_SIG_KEYRING_USER;
-	}
-}
-
-static int bpf_prog_verify_signature(struct bpf_prog *prog, union bpf_attr *attr,
-				     bool is_kernel, s32 *keyring_serial)
-{
-	bpfptr_t usig = make_bpfptr(attr->signature, is_kernel);
-	struct bpf_dynptr_kern sig_ptr, insns_ptr;
-	struct bpf_key *key = NULL;
-	void *sig;
-	int err = 0;
-
-	/*
-	 * Don't attempt to use kmalloc_large or vmalloc for signatures.
-	 * Practical signature for BPF program should be below this limit.
-	 */
-	if (attr->signature_size > KMALLOC_MAX_CACHE_SIZE)
-		return -EINVAL;
-
-	if (system_keyring_id_check(attr->keyring_id) == 0)
-		key = bpf_lookup_system_key(attr->keyring_id);
-	else
-		key = bpf_lookup_user_key(attr->keyring_id, 0);
-
-	if (!key)
-		return -EINVAL;
-
-	sig = kvmemdup_bpfptr(usig, attr->signature_size);
-	if (IS_ERR(sig)) {
-		bpf_key_put(key);
-		return PTR_ERR(sig);
-	}
-
-	bpf_dynptr_init(&sig_ptr, sig, BPF_DYNPTR_TYPE_LOCAL, 0,
-			attr->signature_size);
-	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 (!err)
-		*keyring_serial = bpf_key_serial(key);
-	bpf_key_put(key);
-	kvfree(sig);
-	return err;
-}
-
 static int bpf_prog_mark_insn_arrays_ready(struct bpf_prog *prog)
 {
 	int err;
@@ -3133,17 +3074,8 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, struct bpf_log_at
 
 	/* eBPF programs must be GPL compatible to use GPL-ed functions */
 	prog->gpl_compatible = license_is_gpl_compatible(license) ? 1 : 0;
-	if (attr->signature) {
-		err = bpf_prog_verify_signature(prog, attr, uattr.is_kernel,
-						&prog->aux->sig.keyring_serial);
-		if (err)
-			goto free_prog;
-		prog->aux->sig.keyring_type = bpf_classify_keyring(attr->keyring_id);
-		prog->aux->sig.verdict = BPF_SIG_VERIFIED;
-	} else {
-		prog->aux->sig.keyring_type = BPF_SIG_KEYRING_NONE;
-		prog->aux->sig.verdict = BPF_SIG_UNSIGNED;
-	}
+	prog->aux->sig.keyring_type = BPF_SIG_KEYRING_NONE;
+	prog->aux->sig.verdict = BPF_SIG_UNSIGNED;
 	prog->orig_prog = NULL;
 	prog->jited = 0;
 
@@ -3189,10 +3121,6 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, struct bpf_log_at
 	if (err < 0)
 		goto free_prog;
 
-	err = security_bpf_prog_load(prog, attr, token, uattr.is_kernel);
-	if (err)
-		goto free_prog;
-
 	/* run eBPF verifier */
 	err = bpf_check(&prog, attr, uattr, attr_log);
 	if (err < 0)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e227c76a8dd9..65f53128fc33 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -22,6 +22,8 @@
 #include <linux/ctype.h>
 #include <linux/error-injection.h>
 #include <linux/bpf_lsm.h>
+#include <linux/security.h>
+#include <linux/verification.h>
 #include <linux/btf_ids.h>
 #include <linux/poison.h>
 #include <linux/module.h>
@@ -2554,6 +2556,10 @@ fd_array_get_btf_sparse(struct bpf_verifier_env *env, u32 idx)
 
 static struct btf *fd_array_get_btf(struct bpf_verifier_env *env, u32 idx)
 {
+	if (env->signature) {
+		verbose(env, "signed program cannot bind any BTF\n");
+		return ERR_PTR(-EACCES);
+	}
 	if (env->fd_array)
 		return fd_array_get_btf_continuous(env, idx);
 	if (!bpfptr_is_null(env->fd_array_raw))
@@ -17648,6 +17654,11 @@ static int __add_used_btf(struct bpf_verifier_env *env, struct btf *btf)
 		if (env->used_btfs[i].btf == btf)
 			goto ret_put;
 
+	if (env->signature) {
+		verbose(env, "signed program cannot bind any BTF\n");
+		ret = -EACCES;
+		goto ret_put;
+	}
 	if (env->used_btf_cnt >= MAX_USED_BTFS) {
 		verbose(env, "The total number of btfs per program has reached the limit of %u\n",
 			MAX_USED_BTFS);
@@ -17930,6 +17941,12 @@ static int __add_used_map(struct bpf_verifier_env *env, struct bpf_map *map)
 		if (env->used_maps[i] == map)
 			return i;
 
+	if (env->signature &&
+	    env->prog->aux->sig.verdict == BPF_SIG_VERIFIED) {
+		verbose(env, "signed program cannot bind map '%s' not covered by the signature\n",
+			map->name);
+		return -EACCES;
+	}
 	if (env->used_map_cnt >= MAX_USED_MAPS) {
 		verbose(env, "The total number of maps per program has reached the limit of %u\n",
 			MAX_USED_MAPS);
@@ -18013,6 +18030,10 @@ static int fd_array_get_map_idx(struct bpf_verifier_env *env, u32 idx)
 {
 	if (env->fd_array)
 		return fd_array_get_map_idx_continuous(env, idx);
+	if (env->signature) {
+		verbose(env, "signed program must bind maps via a continuous fd_array (fd_array_cnt)\n");
+		return -EACCES;
+	}
 	if (!bpfptr_is_null(env->fd_array_raw))
 		return fd_array_get_map_idx_sparse(env, idx);
 
@@ -18291,6 +18312,10 @@ static int check_and_resolve_insns(struct bpf_verifier_env *env)
 				map_idx = fd_array_get_map_idx(env, insn[0].imm);
 				break;
 			default:
+				if (env->signature) {
+					verbose(env, "signed program cannot reference a map by fd, only via fd_array index\n");
+					return -EINVAL;
+				}
 				map_idx = add_used_map(env, insn[0].imm);
 				break;
 			}
@@ -19872,6 +19897,139 @@ int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	return 0;
 }
 
+static enum bpf_sig_keyring bpf_classify_keyring(s32 keyring_id)
+{
+	switch (keyring_id) {
+	case 0:
+		return BPF_SIG_KEYRING_BUILTIN;
+	case (s32)(unsigned long)VERIFY_USE_SECONDARY_KEYRING:
+		return BPF_SIG_KEYRING_SECONDARY;
+	case (s32)(unsigned long)VERIFY_USE_PLATFORM_KEYRING:
+		return BPF_SIG_KEYRING_PLATFORM;
+	default:
+		return BPF_SIG_KEYRING_USER;
+	}
+}
+
+/*
+ * Verify the PKCS#7 signature of a loaded program. Called from bpf_check()
+ * once the program's metadata maps have been resolved into used_maps, so
+ * the exact maps folded into the signature are the ones the program binds.
+ *
+ * The signature covers the instructions followed by the frozen contents of
+ * each map, in @maps order: insns || map_0 || map_1 || [...]. On success the
+ * verdict and keyring info are recorded on prog->aux.
+ */
+static int bpf_prog_verify_signature(struct bpf_verifier_env *env,
+				     union bpf_attr *attr, bool is_kernel)
+{
+	bpfptr_t usig = make_bpfptr(attr->signature, is_kernel);
+	struct bpf_dynptr_kern sig_ptr, data_ptr;
+	struct bpf_prog *prog = env->prog;
+	struct bpf_map **maps = env->used_maps;
+	struct bpf_key *key = NULL;
+	void *sig, *data = NULL;
+	u32 map_cnt = env->used_map_cnt;
+	u32 i, off, insns_sz;
+	u64 data_sz;
+	int err = 0;
+
+	/*
+	 * Don't attempt to use kmalloc_large or vmalloc for signatures.
+	 * Practical signature for BPF program should be below this limit.
+	 */
+	if (attr->signature_size > KMALLOC_MAX_CACHE_SIZE)
+		return -EINVAL;
+	if (system_keyring_id_check(attr->keyring_id) == 0)
+		key = bpf_lookup_system_key(attr->keyring_id);
+	else
+		key = bpf_lookup_user_key(attr->keyring_id, 0);
+	if (!key) {
+		verbose(env, "cannot resolve signing keyring with keyring_id %d\n",
+			attr->keyring_id);
+		return -EINVAL;
+	}
+
+	sig = kvmemdup_bpfptr(usig, attr->signature_size);
+	if (IS_ERR(sig)) {
+		bpf_key_put(key);
+		return PTR_ERR(sig);
+	}
+
+	insns_sz = prog->len * sizeof(struct bpf_insn);
+	data_sz = insns_sz;
+	for (i = 0; i < map_cnt; i++) {
+		struct bpf_map *map = maps[i];
+
+		if (map->map_type != BPF_MAP_TYPE_ARRAY ||
+		    !map->ops->map_direct_value_addr) {
+			verbose(env, "signed program metadata map '%s' must be an array\n",
+				map->name);
+			err = -EINVAL;
+			goto out;
+		}
+		if (!READ_ONCE(map->frozen)) {
+			verbose(env, "signed program metadata map '%s' must be frozen\n",
+				map->name);
+			err = -EPERM;
+			goto out;
+		}
+		if (!map->excl_prog_sha) {
+			verbose(env, "signed program metadata map '%s' must be exclusive\n",
+				map->name);
+			err = -EPERM;
+			goto out;
+		}
+		data_sz += map->value_size;
+	}
+	if (bpf_dynptr_check_size(data_sz)) {
+		verbose(env, "signed payload too large: %llu bytes\n", data_sz);
+		err = -E2BIG;
+		goto out;
+	}
+	data = kvmalloc(data_sz, GFP_KERNEL_ACCOUNT | __GFP_ZERO);
+	if (!data) {
+		err = -ENOMEM;
+		goto out;
+	}
+	memcpy(data, prog->insnsi, insns_sz);
+	off = insns_sz;
+	for (i = 0; i < map_cnt; i++) {
+		struct bpf_map *map = maps[i];
+		u64 addr;
+
+		err = map->ops->map_direct_value_addr(map, &addr, 0);
+		if (err) {
+			verbose(env, "failed to read signed metadata map '%s': %d\n",
+				map->name, err);
+			goto out;
+		}
+		memcpy(data + off, (void *)(unsigned long)addr,
+		       map->value_size);
+		off += map->value_size;
+	}
+
+	bpf_dynptr_init(&data_ptr, data, BPF_DYNPTR_TYPE_LOCAL, 0, data_sz);
+	bpf_dynptr_init(&sig_ptr, sig, BPF_DYNPTR_TYPE_LOCAL, 0,
+			attr->signature_size);
+
+	err = bpf_verify_pkcs7_signature((struct bpf_dynptr *)&data_ptr,
+					 (struct bpf_dynptr *)&sig_ptr, key);
+	if (err) {
+		verbose(env, "signature verification failed: %d\n", err);
+	} else {
+		verbose(env, "signature verification passed\n");
+		prog->aux->sig.keyring_serial = bpf_key_serial(key);
+		prog->aux->sig.keyring_type = bpf_classify_keyring(attr->keyring_id);
+		prog->aux->sig.verdict = BPF_SIG_VERIFIED;
+	}
+out:
+	kvfree(data);
+	bpf_key_put(key);
+	kvfree(sig);
+	return err;
+}
+
 int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 	      struct bpf_log_attr *attr_log)
 {
@@ -19902,6 +20060,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 	env->bypass_spec_v1 = bpf_bypass_spec_v1(env->prog->aux->token);
 	env->bypass_spec_v4 = bpf_bypass_spec_v4(env->prog->aux->token);
 	env->bpf_capable = is_priv = bpf_token_capable(env->prog->aux->token, CAP_BPF);
+	env->signature = attr->signature;
 
 	/* user could have requested verbose verifier output
 	 * and supplied buffer to store the verification trace
@@ -19909,11 +20068,27 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 	ret = bpf_vlog_init(&env->log, attr_log->level, attr_log->ubuf, attr_log->size);
 	if (ret)
 		goto err_free_env;
+	if (env->signature) {
+		ret = bpf_prog_calc_tag(env->prog);
+		if (ret < 0)
+			goto err_prep;
+	}
 
 	ret = process_fd_array(env, attr, uattr);
 	if (ret)
 		goto err_prep;
 
+	if (env->signature) {
+		ret = bpf_prog_verify_signature(env, attr, uattr.is_kernel);
+		if (ret)
+			goto err_prep;
+	}
+
+	ret = security_bpf_prog_load(env->prog, attr, env->prog->aux->token,
+				     uattr.is_kernel);
+	if (ret)
+		goto err_prep;
+
 	bpf_get_btf_vmlinux();
 
 	/* grab the mutex to protect few globals used by verifier */
-- 
2.43.0

[PATCH bpf-next v4 4/9] libbpf: Drop in-loader metadata check for load-time verification

[Daniel Borkmann]

The signed gen_loader used to police its own metadata map from within
BPF: emit_signature_match() read the kernel-cached map->sha[] back
through hardcoded struct bpf_map offsets and compared it against a hash
that compute_sha_update_offsets() baked into the signed instructions,
after a BPF_OBJ_GET_INFO_BY_FD round-trip to populate map->sha[].

The kernel now verifies the metadata at BPF_PROG_LOAD time by folding
the frozen contents of the loader's exclusive fd_array maps into the
signature, so the loader no longer checks anything itself. Generated
loaders thus carry no verification logic of their own anymore: Nothing
in the signing chain depends on emitted loader bytecode doing the right
thing.

On the loading side, skel_internal.h now sets fd_array_cnt for a signed
load so the kernel scans fd_array for the exclusive metadata map -
still frozen, as the kernel requires - and the BPF_OBJ_GET_INFO_BY_FD
round-trip to populate map->sha[] is gone. The struct bpf_map layout
BUILD_BUG_ON()s on the kernel side are removed as well: they only
pinned the ABI for the in-BPF read of map->sha[] that is no longer
needed. Same for the map->excl member. Note: gen_hash is retained; it
still marks a loader as signed so an untrusted host cannot re-dimension
maps or override initial values now covered by the signature.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 include/linux/bpf.h              |  1 -
 kernel/bpf/syscall.c             |  7 ---
 tools/lib/bpf/bpf_gen_internal.h |  1 -
 tools/lib/bpf/gen_loader.c       | 76 +++-----------------------------
 tools/lib/bpf/libbpf_internal.h  |  1 -
 tools/lib/bpf/skel_internal.h    | 31 +------------
 6 files changed, 9 insertions(+), 108 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index ba09795e0bfd..2e0f12fb4cea 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -299,7 +299,6 @@ struct bpf_map_owner {
 
 struct bpf_map {
 	u8 sha[SHA256_DIGEST_SIZE];
-	u32 excl;
 	const struct bpf_map_ops *ops;
 	struct bpf_map *inner_map_meta;
 #ifdef CONFIG_SECURITY
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e898fad01aaf..358f2b0ce2bd 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1598,13 +1598,6 @@ static int map_create_alloc(union bpf_attr *attr, bpfptr_t uattr, struct bpf_ver
 			err = -EFAULT;
 			goto free_map;
 		}
-
-		/* See libbpf: emit_signature_match() */
-		BUILD_BUG_ON(offsetof(struct bpf_map, excl) != SHA256_DIGEST_SIZE);
-		BUILD_BUG_ON(!__same_type(map->excl, u32));
-		BUILD_BUG_ON(offsetof(struct bpf_map, sha)  != 0);
-		BUILD_BUG_ON(!__same_type(map->sha, u8[SHA256_DIGEST_SIZE]));
-		map->excl = 1;
 	} else if (attr->excl_prog_hash_size) {
 		bpf_log(log, "Invalid excl_prog_hash_size.\n");
 		err = -EINVAL;
diff --git a/tools/lib/bpf/bpf_gen_internal.h b/tools/lib/bpf/bpf_gen_internal.h
index 49af4260b8e6..042569187752 100644
--- a/tools/lib/bpf/bpf_gen_internal.h
+++ b/tools/lib/bpf/bpf_gen_internal.h
@@ -51,7 +51,6 @@ struct bpf_gen {
 	__u32 nr_ksyms;
 	int fd_array;
 	int nr_fd_array;
-	int hash_insn_offset[SHA256_DWORD_SIZE];
 };
 
 void bpf_gen__init(struct bpf_gen *gen, int log_level, int nr_progs, int nr_maps);
diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index c7f2d2ac7bb3..6e3dd5242761 100644
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -111,7 +111,6 @@ static void emit2(struct bpf_gen *gen, struct bpf_insn insn1, struct bpf_insn in
 
 static int add_data(struct bpf_gen *gen, const void *data, __u32 size);
 static void emit_sys_close_blob(struct bpf_gen *gen, int blob_off);
-static void emit_signature_match(struct bpf_gen *gen);
 
 void bpf_gen__init(struct bpf_gen *gen, int log_level, int nr_progs, int nr_maps)
 {
@@ -154,8 +153,6 @@ void bpf_gen__init(struct bpf_gen *gen, int log_level, int nr_progs, int nr_maps
 	/* R7 contains the error code from sys_bpf. Copy it into R0 and exit. */
 	emit(gen, BPF_MOV64_REG(BPF_REG_0, BPF_REG_7));
 	emit(gen, BPF_EXIT_INSN());
-	if (OPTS_GET(gen->opts, gen_hash, false))
-		emit_signature_match(gen);
 }
 
 static int add_data(struct bpf_gen *gen, const void *data, __u32 size)
@@ -377,8 +374,6 @@ static void emit_sys_close_blob(struct bpf_gen *gen, int blob_off)
 	__emit_sys_close(gen);
 }
 
-static void compute_sha_update_offsets(struct bpf_gen *gen);
-
 int bpf_gen__finish(struct bpf_gen *gen, int nr_progs, int nr_maps)
 {
 	int i;
@@ -408,9 +403,6 @@ int bpf_gen__finish(struct bpf_gen *gen, int nr_progs, int nr_maps)
 	if (!gen->error) {
 		struct gen_loader_opts *opts = gen->opts;
 
-		if (OPTS_GET(opts, gen_hash, false))
-			compute_sha_update_offsets(gen);
-
 		opts->insns = gen->insn_start;
 		opts->insns_sz = gen->insn_cur - gen->insn_start;
 		opts->data = gen->data_start;
@@ -460,22 +452,6 @@ void bpf_gen__free(struct bpf_gen *gen)
 	_val;							\
 })
 
-static void compute_sha_update_offsets(struct bpf_gen *gen)
-{
-	__u64 sha[SHA256_DWORD_SIZE];
-	__u64 sha_dw;
-	int i;
-
-	libbpf_sha256(gen->data_start, gen->data_cur - gen->data_start, (__u8 *)sha);
-	for (i = 0; i < SHA256_DWORD_SIZE; i++) {
-		struct bpf_insn *insn =
-			(struct bpf_insn *)(gen->insn_start + gen->hash_insn_offset[i]);
-		sha_dw = tgt_endian(sha[i]);
-		insn[0].imm = (__u32)sha_dw;
-		insn[1].imm = sha_dw >> 32;
-	}
-}
-
 void bpf_gen__load_btf(struct bpf_gen *gen, const void *btf_raw_data,
 		       __u32 btf_raw_size)
 {
@@ -557,8 +533,9 @@ void bpf_gen__map_create(struct bpf_gen *gen,
 	 * Conditionally update max_entries from the host-supplied loader
 	 * ctx. This sizes the map at runtime, but for a signed loader
 	 * (gen_hash) it would let an untrusted host re-dimension the
-	 * program's maps after emit_signature_match(), outside what the
-	 * signature attests to. Keep the signer-provided max_entries
+	 * program's maps, outside what the signature attests to: the
+	 * metadata blob is covered by the program signature and verified
+	 * by the kernel at load time. Keep the signer-provided max_entries
 	 * baked into the blob in that case.
 	 */
 	if (map_idx >= 0 && !OPTS_GET(gen->opts, gen_hash, false))
@@ -596,45 +573,6 @@ void bpf_gen__map_create(struct bpf_gen *gen,
 		emit_sys_close_stack(gen, stack_off(inner_map_fd));
 }
 
-static void emit_signature_match(struct bpf_gen *gen)
-{
-	__s64 off;
-	int i;
-
-	/*
-	 * Reject if the metadata map is not exclusive. Without exclusivity
-	 * the cached map->sha[] verified above can be stale: another BPF
-	 * program with map access could have mutated the contents between
-	 * BPF_OBJ_GET_INFO_BY_FD and loader execution.
-	 */
-	emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX,
-					 0, 0, 0, 0));
-	emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, SHA256_DIGEST_LENGTH));
-	off = -(gen->insn_cur - gen->insn_start - gen->cleanup_label) / 8 - 2;
-	if (is_simm16(off)) {
-		emit(gen, BPF_MOV64_IMM(BPF_REG_7, -EINVAL));
-		emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 1, off));
-	} else {
-		gen->error = -ERANGE;
-	}
-
-	for (i = 0; i < SHA256_DWORD_SIZE; i++) {
-		emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX,
-						 0, 0, 0, 0));
-		emit(gen, BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1, i * sizeof(__u64)));
-		gen->hash_insn_offset[i] = gen->insn_cur - gen->insn_start;
-		emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_3, 0, 0, 0, 0, 0));
-
-		off = -(gen->insn_cur - gen->insn_start - gen->cleanup_label) / 8 - 2;
-		if (is_simm16(off)) {
-			emit(gen, BPF_MOV64_IMM(BPF_REG_7, -EINVAL));
-			emit(gen, BPF_JMP_REG(BPF_JNE, BPF_REG_2, BPF_REG_3, off));
-		} else {
-			gen->error = -ERANGE;
-		}
-	}
-}
-
 void bpf_gen__record_attach_target(struct bpf_gen *gen, const char *attach_name,
 				   enum bpf_attach_type type)
 {
@@ -1211,10 +1149,10 @@ void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *pvalue,
 	 * }
 	 *
 	 * The runtime initial_value comes from the host-supplied loader
-	 * ctx and would overwrite the blob value after emit_signature_match()
-	 * has already validated map->sha[]. For a signed loader (gen_hash)
-	 * the attested blob value must be authoritative, so skip the override
-	 * and leave the hashed value in place.
+	 * ctx and would overwrite the blob value that the program signature
+	 * covers and the kernel verifies at load time. For a signed loader
+	 * (gen_hash) the attested blob value must be authoritative, so skip
+	 * the override and leave the signed value in place.
 	 */
 	if (!OPTS_GET(gen->opts, gen_hash, false)) {
 		emit(gen, BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_6,
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 04cd303fb5a8..d5b7db703b3f 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -768,7 +768,6 @@ int elf_resolve_pattern_offsets(const char *binary_path, const char *pattern,
 int probe_fd(int fd);
 
 #define SHA256_DIGEST_LENGTH 32
-#define SHA256_DWORD_SIZE SHA256_DIGEST_LENGTH / sizeof(__u64)
 
 void libbpf_sha256(const void *data, size_t len, __u8 out[SHA256_DIGEST_LENGTH]);
 int probe_sys_bpf_ext(void);
diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h
index 74503d358bc8..53fee53d36d5 100644
--- a/tools/lib/bpf/skel_internal.h
+++ b/tools/lib/bpf/skel_internal.h
@@ -18,10 +18,6 @@
 #include "bpf.h"
 #endif
 
-#ifndef SHA256_DIGEST_LENGTH
-#define SHA256_DIGEST_LENGTH 32
-#endif
-
 #ifndef __NR_bpf
 # if defined(__mips__) && defined(_ABIO32)
 #  define __NR_bpf 4355
@@ -320,25 +316,6 @@ static inline int skel_link_create(int prog_fd, int target_fd,
 	return skel_sys_bpf(BPF_LINK_CREATE, &attr, attr_sz);
 }
 
-static inline int skel_obj_get_info_by_fd(int fd)
-{
-	const size_t attr_sz = offsetofend(union bpf_attr, info);
-	__u8 sha[SHA256_DIGEST_LENGTH];
-	struct bpf_map_info info;
-	__u32 info_len = sizeof(info);
-	union bpf_attr attr;
-
-	memset(&info, 0, sizeof(info));
-	info.hash = (long) &sha;
-	info.hash_size = SHA256_DIGEST_LENGTH;
-
-	memset(&attr, 0, attr_sz);
-	attr.info.bpf_fd = fd;
-	attr.info.info = (long) &info;
-	attr.info.info_len = info_len;
-	return skel_sys_bpf(BPF_OBJ_GET_INFO_BY_FD, &attr, attr_sz);
-}
-
 static inline int skel_map_freeze(int fd)
 {
 	const size_t attr_sz = offsetofend(union bpf_attr, map_fd);
@@ -384,12 +361,6 @@ static inline int bpf_load_and_run(struct bpf_load_and_run_opts *opts)
 		set_err;
 		goto out;
 	}
-	err = skel_obj_get_info_by_fd(map_fd);
-	if (err < 0) {
-		opts->errstr = "failed to fetch obj info";
-		set_err;
-		goto out;
-	}
 #endif
 
 	memset(&attr, 0, prog_load_attr_sz);
@@ -400,6 +371,8 @@ static inline int bpf_load_and_run(struct bpf_load_and_run_opts *opts)
 #ifndef __KERNEL__
 	attr.signature = (long) opts->signature;
 	attr.signature_size = opts->signature_sz;
+	if (opts->signature)
+		attr.fd_array_cnt = 1;
 #else
 	if (opts->signature || opts->signature_sz)
 		pr_warn("signatures are not supported from bpf_preload\n");
-- 
2.43.0

[PATCH bpf-next v4 5/9] bpftool: Check EVP_Digest when computing excl_prog_hash

[Daniel Borkmann]

bpftool_prog_sign() ignores the return value of EVP_Digest(). If the
digest computation fails (context allocation failure, or a digest
fetch failure under OpenSSL), EVP_Digest() returns 0 and leaves the
output buffer untouched, but the function still reports success.

Fixes: 40863f4d6ef2 ("bpftool: Add support for signing BPF programs")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 tools/bpf/bpftool/sign.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/sign.c b/tools/bpf/bpftool/sign.c
index f9b742f4bb10..1257dba8ef2f 100644
--- a/tools/bpf/bpftool/sign.c
+++ b/tools/bpf/bpftool/sign.c
@@ -175,8 +175,11 @@ int bpftool_prog_sign(struct bpf_load_and_run_opts *opts)
 		goto cleanup;
 	}
 
-	EVP_Digest(opts->insns, opts->insns_sz, opts->excl_prog_hash,
-		   &opts->excl_prog_hash_sz, EVP_sha256(), NULL);
+	if (EVP_Digest(opts->insns, opts->insns_sz, opts->excl_prog_hash,
+		       &opts->excl_prog_hash_sz, EVP_sha256(), NULL) != 1) {
+		err = -EIO;
+		goto cleanup;
+	}
 
 		bd_out = BIO_new(BIO_s_mem());
 	if (!bd_out) {
-- 
2.43.0

[PATCH bpf-next v4 6/9] bpftool: Cover loader metadata with the program signature

[Daniel Borkmann]

bpftool_prog_sign() signed only the loader instructions. The metadata
blob the loader installs was left to an in-loader hash check, which
the kernel now performs at load time over insns || metadata.

Sign that same concatenation: pass the metadata blob (gen_loader_opts
data) through to bpftool_prog_sign() and feed insns || metadata to
CMS_final(). The excl_prog_hash stays a digest of the instructions
alone; it binds the metadata map to the loader and is matched against
prog->digest by the verifier, independent of what the signature covers.

The signed artifact is now plain data: both bytes the signature
covers are embedded verbatim in the generated skeleton, so signing
and verifying an lskel is an ordinary CMS operation that a signer or
auditor can perform (or reproduce) offline, without analyzing loader
bytecode to establish what the signature actually attests to.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 tools/bpf/bpftool/gen.c  |  2 ++
 tools/bpf/bpftool/sign.c | 17 +++++++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 6ae7262ebe0c..a01d06d22d1a 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -793,6 +793,8 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
 	if (sign_progs) {
 		sopts.insns = opts.insns;
 		sopts.insns_sz = opts.insns_sz;
+		sopts.data = opts.data;
+		sopts.data_sz = opts.data_sz;
 		sopts.excl_prog_hash = prog_sha;
 		sopts.excl_prog_hash_sz = sizeof(prog_sha);
 		sopts.signature = sig_buf;
diff --git a/tools/bpf/bpftool/sign.c b/tools/bpf/bpftool/sign.c
index 1257dba8ef2f..88726a6db6d0 100644
--- a/tools/bpf/bpftool/sign.c
+++ b/tools/bpf/bpftool/sign.c
@@ -135,9 +135,21 @@ int bpftool_prog_sign(struct bpf_load_and_run_opts *opts)
 	CMS_ContentInfo *cms = NULL;
 	long actual_sig_len = 0;
 	X509 *x509 = NULL;
+	void *data = NULL;
+	size_t data_sz;
 	int err = 0;
 
-	bd_in = BIO_new_mem_buf(opts->insns, opts->insns_sz);
+	data_sz = (size_t)opts->insns_sz + opts->data_sz;
+	data = malloc(data_sz);
+	if (!data) {
+		err = -ENOMEM;
+		goto cleanup;
+	}
+	memcpy(data, opts->insns, opts->insns_sz);
+	if (opts->data_sz)
+		memcpy((char *)data + opts->insns_sz, opts->data, opts->data_sz);
+
+	bd_in = BIO_new_mem_buf(data, data_sz);
 	if (!bd_in) {
 		err = -ENOMEM;
 		goto cleanup;
@@ -181,7 +193,7 @@ int bpftool_prog_sign(struct bpf_load_and_run_opts *opts)
 		goto cleanup;
 	}
 
-		bd_out = BIO_new(BIO_s_mem());
+	bd_out = BIO_new(BIO_s_mem());
 	if (!bd_out) {
 		err = -ENOMEM;
 		goto cleanup;
@@ -215,6 +227,7 @@ int bpftool_prog_sign(struct bpf_load_and_run_opts *opts)
 	X509_free(x509);
 	EVP_PKEY_free(private_key);
 	BIO_free(bd_in);
+	free(data);
 	DISPLAY_OSSL_ERR(err < 0);
 	return err;
 }
-- 
2.43.0

[PATCH bpf-next v4 7/9] selftests/bpf: Adjust bpf_map layout in verifier_map_ptr

[Daniel Borkmann]

With write-only excl member removed from struct bpf_map, ops moves
to offset 32 and inner_map_meta to offset 40. Update the expected
verifier message for the former and retarget the latter at the sha
byte array, so the beyond-member-end rejection path stays covered:

  # LDLIBS=-static PKG_CONFIG='pkg-config --static' ./vmtest.sh -- ./test_progs -t verifier_map_ptr
  [...]
  #619/5   verifier_map_ptr/bpf_map_ptr: read non-existent field rejected:OK
  #619/6   verifier_map_ptr/bpf_map_ptr: read non-existent field rejected @unpriv:OK
  #619/7   verifier_map_ptr/bpf_map_ptr: read beyond sha field rejected:OK
  #619/8   verifier_map_ptr/bpf_map_ptr: read beyond sha field rejected @unpriv:OK
  #619/9   verifier_map_ptr/bpf_map_ptr: read ops field accepted:OK
  #619/10  verifier_map_ptr/bpf_map_ptr: read ops field accepted @unpriv:OK
  [...]
  #620     verifier_map_ptr_mixing:OK
  Summary: 2/20 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../selftests/bpf/progs/verifier_map_ptr.c    | 23 ++++++++++---------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/verifier_map_ptr.c b/tools/testing/selftests/bpf/progs/verifier_map_ptr.c
index 166193659870..e0a65835c861 100644
--- a/tools/testing/selftests/bpf/progs/verifier_map_ptr.c
+++ b/tools/testing/selftests/bpf/progs/verifier_map_ptr.c
@@ -72,14 +72,15 @@ __naked void bpf_map_ptr_write_rejected(void)
 
 /*
  * struct bpf_map starts with the SHA256 hash sha[32] at offset 0 (a readable
- * byte array), the u32 excl field at offset 32, and the ops pointer at offset
- * 40. Reading a u32 at offset 41 reaches into the middle of the ops pointer,
- * i.e. a partial pointer access, which is rejected.
+ * byte array), followed by the ops pointer at offset 32 and the inner_map_meta
+ * pointer at offset 40. Reading a u32 at offset 41 reaches into the middle of
+ * the inner_map_meta pointer, i.e. a partial pointer access, which is
+ * rejected.
  */
 SEC("socket")
 __description("bpf_map_ptr: read non-existent field rejected")
 __failure
-__msg("cannot access ptr member ops with moff 40 in struct bpf_map with off 41 size 4")
+__msg("cannot access ptr member inner_map_meta with moff 40 in struct bpf_map with off 41 size 4")
 __failure_unpriv
 __msg_unpriv("access is allowed only to CAP_PERFMON and CAP_SYS_ADMIN")
 __flag(BPF_F_ANY_ALIGNMENT)
@@ -97,23 +98,23 @@ __naked void read_non_existent_field_rejected(void)
 }
 
 /*
- * The u32 excl field spans offsets 32..35 (mend 36). Reading a u32 at offset
- * 33 starts inside excl but extends past its end, which the verifier rejects
+ * The sha byte array spans offsets 0..31 (mend 32). Reading a u32 at offset
+ * 30 starts inside sha but extends past its end, which the verifier rejects
  * as an out-of-bounds scalar access.
  */
 SEC("socket")
-__description("bpf_map_ptr: read beyond excl field rejected")
+__description("bpf_map_ptr: read beyond sha field rejected")
 __failure
-__msg("access beyond the end of member excl (mend:36) in struct bpf_map with off 33 size 4")
+__msg("access beyond the end of member sha (mend:32) in struct bpf_map with off 30 size 4")
 __failure_unpriv
 __msg_unpriv("access is allowed only to CAP_PERFMON and CAP_SYS_ADMIN")
 __flag(BPF_F_ANY_ALIGNMENT)
-__naked void read_beyond_excl_field_rejected(void)
+__naked void read_beyond_sha_field_rejected(void)
 {
 	asm volatile ("					\
 	r6 = 0;						\
 	r1 = %[map_array_48b] ll;			\
-	r6 = *(u32*)(r1 + 33);				\
+	r6 = *(u32*)(r1 + 30);				\
 	r0 = 1;						\
 	exit;						\
 "	:
@@ -131,7 +132,7 @@ __naked void ptr_read_ops_field_accepted(void)
 	asm volatile ("					\
 	r6 = 0;						\
 	r1 = %[map_array_48b] ll;			\
-	r6 = *(u64*)(r1 + 40);				\
+	r6 = *(u64*)(r1 + 32);				\
 	r0 = 1;						\
 	exit;						\
 "	:
-- 
2.43.0

[PATCH bpf-next v4 8/9] selftests/bpf: Verify load-time signed loader metadata

[Daniel Borkmann]

The signed gen_loader no longer checks its metadata map from within
BPF; the kernel does it at BPF_PROG_LOAD by folding the loader's frozen
exclusive fd_array maps into the signature. Exercise that path end to
end. Extend with more test cases (e.g. map-less program, asserting the
LSM admission hook observes BPF_SIG_UNSIGNED and BPF_SIG_VERIFIED), and
retire the subtests that asserted the old in-loader check, which no
longer exists.

  # LDLIBS=-static PKG_CONFIG='pkg-config --static' ./vmtest.sh -- ./test_progs -t signed_loader
  [...]
  #411/1   signed_loader/loadtime_no_map:OK
  #411/2   signed_loader/loadtime_with_map:OK
  #411/3   signed_loader/metadata_match:OK
  #411/4   signed_loader/signature_enforced:OK
  #411/5   signed_loader/signed_nonexcl_fd_array_rejected:OK
  #411/6   signed_loader/signed_unfrozen_fd_array_rejected:OK
  #411/7   signed_loader/signed_nonarray_fd_array_rejected:OK
  #411/8   signed_loader/signed_btf_fd_array_rejected:OK
  #411/9   signed_loader/signed_module_kfunc_rejected:OK
  #411/10  signed_loader/signature_failure_logs:OK
  #411/11  signed_loader/signature_too_large:OK
  #411/12  signed_loader/signature_bad_keyring:OK
  #411/13  signed_loader/metadata_ctx_max_entries_ignored:OK
  #411/14  signed_loader/metadata_ctx_initial_value_ignored:OK
  #411/15  signed_loader/signature_authenticates_insns:OK
  #411/16  signed_loader/signature_authenticates_metadata:OK
  #411/17  signed_loader/hash_requires_frozen:OK
  #411/18  signed_loader/no_update_after_freeze:OK
  #411/19  signed_loader/freeze_writable_mmap:OK
  #411/20  signed_loader/no_writable_mmap_frozen:OK
  #411/21  signed_loader/map_hash_matches_libbpf:OK
  #411/22  signed_loader/map_hash_multi_element:OK
  #411/23  signed_loader/map_hash_bad_size:OK
  #411/24  signed_loader/map_hash_unsupported_type:OK
  #411/25  signed_loader/lsm_signature_verdict:OK
  #411/26  signed_loader/signed_no_fd_array:OK
  #411/27  signed_loader/signed_map_by_fd_rejected:OK
  #411/28  signed_loader/signed_sparse_fd_array_rejected:OK
  #411     signed_loader:OK
  Summary: 1/28 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../selftests/bpf/prog_tests/signed_loader.c  | 1004 ++++++++++++++---
 .../selftests/bpf/progs/test_signed_loader.c  |    9 +-
 2 files changed, 845 insertions(+), 168 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/signed_loader.c b/tools/testing/selftests/bpf/prog_tests/signed_loader.c
index 5fc417e31fc6..56d1f072de4c 100644
--- a/tools/testing/selftests/bpf/prog_tests/signed_loader.c
+++ b/tools/testing/selftests/bpf/prog_tests/signed_loader.c
@@ -11,6 +11,8 @@
 #include <linux/keyctl.h>
 #include <linux/bpf.h>
 
+#include <bpf/btf.h>
+
 #include "bpf/libbpf_internal.h" /* for libbpf_sha256() */
 #include "bpf/skel_internal.h"	 /* for loader ctx layout (bpf_loader_ctx etc) */
 
@@ -19,8 +21,6 @@
 #include "test_signed_loader_data.skel.h"
 #include "test_signed_loader_lsm.skel.h"
 
-#define SIG_MATCH_INSNS 33 /* excl (5) + 4 * sha-dword (7) */
-
 enum {
 	BPF_SIG_UNSIGNED = 0,
 	BPF_SIG_VERIFIED,
@@ -35,7 +35,8 @@ enum {
 };
 
 static int load_loader(const void *insns, __u32 insns_sz, int map_fd,
-		       const void *sig, __u32 sig_sz, __s32 keyring_id)
+		       const void *sig, __u32 sig_sz, __s32 keyring_id,
+		       __u32 fd_array_cnt)
 {
 	union bpf_attr attr;
 	int fd;
@@ -52,6 +53,7 @@ static int load_loader(const void *insns, __u32 insns_sz, int map_fd,
 		attr.signature_size = sig_sz;
 		attr.keyring_id = keyring_id;
 	}
+	attr.fd_array_cnt = fd_array_cnt;
 	memcpy(attr.prog_name, "__loader.prog", sizeof("__loader.prog"));
 	fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
 		     offsetofend(union bpf_attr, keyring_id));
@@ -62,14 +64,12 @@ static int run_gen_loader(const void *insns, __u32 insns_sz,
 			  const void *data, __u32 data_sz,
 			  const void *excl, __u32 excl_sz,
 			  const void *sig, __u32 sig_sz,
-			  bool get_hash, void *ctx, __u32 ctx_sz, bool *loader_ran)
+			  void *ctx, __u32 ctx_sz, bool *loader_ran)
 {
 	LIBBPF_OPTS(bpf_map_create_opts, mopts,
 		    .excl_prog_hash = excl,
 		    .excl_prog_hash_size = excl_sz);
-	__u8 hbuf[SHA256_DIGEST_LENGTH];
-	struct bpf_map_info info;
-	__u32 ilen = sizeof(info), key = 0;
+	__u32 key = 0;
 	union bpf_attr attr;
 	int map_fd, prog_fd, ret;
 
@@ -87,15 +87,6 @@ static int run_gen_loader(const void *insns, __u32 insns_sz,
 		ret = -errno;
 		goto out_map;
 	}
-	if (get_hash) {
-		memset(&info, 0, sizeof(info));
-		info.hash = ptr_to_u64(hbuf);
-		info.hash_size = sizeof(hbuf);
-		if (bpf_map_get_info_by_fd(map_fd, &info, &ilen)) {
-			ret = -errno;
-			goto out_map;
-		}
-	}
 
 	memset(&attr, 0, sizeof(attr));
 	attr.prog_type = BPF_PROG_TYPE_SYSCALL;
@@ -108,6 +99,7 @@ static int run_gen_loader(const void *insns, __u32 insns_sz,
 		attr.signature = ptr_to_u64(sig);
 		attr.signature_size = sig_sz;
 		attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
+		attr.fd_array_cnt = 1;
 	}
 	memcpy(attr.prog_name, "__loader.prog", sizeof("__loader.prog"));
 	prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
@@ -236,79 +228,6 @@ static int sign_buf(const char *dir, const void *buf, __u32 len,
 	return ret;
 }
 
-static void check_sig_match_shape(const struct bpf_insn *in, int n)
-{
-	int a = -1, cleanup = -1, i, base, t, br[5], nb = 0;
-
-	/* BPF_PSEUDO_MAP_IDX (the struct bpf_map * form) is used only here. */
-	for (i = 0; i + 1 < n; i++) {
-		if (in[i].code == (BPF_LD | BPF_IMM | BPF_DW) &&
-		    in[i].src_reg == BPF_PSEUDO_MAP_IDX) {
-			a = i;
-			break;
-		}
-	}
-	if (!ASSERT_GE(a, 0, "emit_signature_match present"))
-		return;
-	if (!ASSERT_LE(a + SIG_MATCH_INSNS, n, "block fits in program"))
-		return;
-
-	/* excl check: r2 = *(u32 *)(map + 32); if r2 != 1 goto cleanup */
-	ASSERT_EQ(in[a + 2].code, (BPF_LDX | BPF_MEM | BPF_W), "excl load width");
-	ASSERT_EQ(in[a + 2].off, SHA256_DIGEST_LENGTH, "excl field offset");
-	ASSERT_EQ(in[a + 4].code, (BPF_JMP | BPF_JNE | BPF_K), "excl branch op");
-	ASSERT_EQ(in[a + 4].imm, 1, "excl compared to 1");
-	br[nb++] = a + 4;
-
-	/* 4 sha-dword checks: r2 = *(u64 *)(map + i*8); if r2 != r3 goto cleanup */
-	for (i = 0; i < 4; i++) {
-		base = a + 5 + i * 7;
-		ASSERT_EQ(in[base + 2].code, (BPF_LDX | BPF_MEM | BPF_DW), "sha load width");
-		ASSERT_EQ(in[base + 2].off, i * 8, "sha dword offset");
-		ASSERT_EQ(in[base + 3].code, (BPF_LD | BPF_IMM | BPF_DW), "sha imm64 (H_meta)");
-		ASSERT_EQ(in[base + 6].code, (BPF_JMP | BPF_JNE | BPF_X), "sha branch op");
-		br[nb++] = base + 6;
-	}
-
-	/*
-	 * Locate the real cleanup label so we can pin the exact jump target,
-	 * not just "some backward label". bpf_gen__init() emits the cleanup
-	 * block as a prog-fd close loop whose first instruction is the label
-	 * every error branch jumps to.
-	 */
-	for (i = 0; i + 2 < a; i++) {
-		if (in[i].code == (BPF_LDX | BPF_MEM | BPF_W) &&
-		    in[i].dst_reg == BPF_REG_1 && in[i].src_reg == BPF_REG_10 &&
-		    in[i + 1].code == (BPF_JMP | BPF_JSLE | BPF_K) &&
-		    in[i + 1].dst_reg == BPF_REG_1 && in[i + 1].imm == 0 &&
-		    in[i + 1].off == 1 &&
-		    in[i + 2].code == (BPF_JMP | BPF_CALL) &&
-		    in[i + 2].imm == BPF_FUNC_sys_close) {
-			cleanup = i;
-			break;
-		}
-	}
-	if (!ASSERT_GE(cleanup, 0, "cleanup label located"))
-		return;
-	for (i = 0; i < nb; i++) {
-		t = br[i] + 1 + in[br[i]].off;
-		ASSERT_EQ(t, cleanup, "sig-match lands on cleanup");
-	}
-	/*
-	 * Same invariant for every other cleanup-bound jump in the program:
-	 * emit_check_err() is the only source of "if (r7 < 0) goto cleanup",
-	 * so each of those must also resolve exactly to cleanup.
-	 */
-	for (i = 0, t = 0; i < n; i++) {
-		if (in[i].code != (BPF_JMP | BPF_JSLT | BPF_K) ||
-		    in[i].dst_reg != BPF_REG_7 || in[i].imm != 0 || in[i].off >= 0)
-			continue;
-		ASSERT_EQ(i + 1 + in[i].off, cleanup, "err-check lands on cleanup");
-		t++;
-	}
-	ASSERT_GT(t, 0, "found emit_check_err jumps");
-}
-
 struct gen_loader_fixture {
 	struct test_signed_loader *skel;
 	struct gen_loader_opts gopts;
@@ -372,16 +291,6 @@ static void gen_loader_fixture_fini(struct gen_loader_fixture *f)
 	test_signed_loader__destroy(f->skel);
 }
 
-static void metadata_check_shape(void)
-{
-	struct gen_loader_fixture f;
-
-	if (gen_loader_fixture_init(&f) == 0)
-		check_sig_match_shape((const struct bpf_insn *)f.gopts.insns,
-				      f.gopts.insns_sz / sizeof(struct bpf_insn));
-	gen_loader_fixture_fini(&f);
-}
-
 static void metadata_match(void)
 {
 	struct gen_loader_fixture f;
@@ -391,94 +300,263 @@ static void metadata_match(void)
 	if (gen_loader_fixture_init(&f) == 0) {
 		r = run_gen_loader(f.gopts.insns, f.gopts.insns_sz, f.blob,
 				   f.data_sz, f.excl, sizeof(f.excl), NULL, 0,
-				   true, f.ctx, f.ctx_sz, &ran);
+				   f.ctx, f.ctx_sz, &ran);
 		ASSERT_TRUE(ran, "loader ran");
 		ASSERT_EQ(r, 0, "honest loader retval");
 	}
 	gen_loader_fixture_fini(&f);
 }
 
-static void metadata_sha_mismatch(void)
+static void signature_enforced(void)
 {
+	static const __u8 junk[64] = { 0x30, 0x42, 0x13, 0x37, };
 	struct gen_loader_fixture f;
-	bool ran;
-	int r;
+	int fd;
 
 	if (gen_loader_fixture_init(&f) == 0) {
 		/*
-		 * blob[0] lives in the loader's fd_array scratch (first add_data in
-		 * bpf_gen__init); a 0-map program never reads it, so flipping it
-		 * changes only map->sha. The metadata check is the only thing that
-		 * can notice -> isolates emit_signature_match.
+		 * A present-but-invalid signature (the cert bytes are not a
+		 * PKCS#7 signature) must be rejected at load: the signature
+		 * path is honored, not ignored. (The valid path is covered by
+		 * the signed lskels.) Pin -EBADMSG, the PKCS#7 parse failure:
+		 * a looser fd < 0 check could also be satisfied by the sparse
+		 * fd_array rejection (-EACCES) that the loader's map reference
+		 * would trip even if the signature were silently ignored.
 		 */
-		f.blob[0] ^= 0xff;
-		r = run_gen_loader(f.gopts.insns, f.gopts.insns_sz, f.blob,
-				   f.data_sz, f.excl, sizeof(f.excl), NULL, 0,
-				   true, f.ctx, f.ctx_sz, &ran);
-		ASSERT_TRUE(ran, "loader ran");
-		ASSERT_EQ(r, -EINVAL, "tampered blob rejected by emit_signature_match");
+		fd = load_loader(f.gopts.insns, f.gopts.insns_sz, -1, junk,
+				 sizeof(junk), KEY_SPEC_SESSION_KEYRING, 0);
+		ASSERT_EQ(fd, -EBADMSG, "invalid signature rejected at load");
 	}
 	gen_loader_fixture_fini(&f);
 }
 
-static void metadata_not_exclusive(void)
+static void signed_nonexcl_fd_array_rejected(void)
 {
+	static const __u8 junk[64] = { 0x30, 0x42, 0x13, 0x37, };
 	struct gen_loader_fixture f;
-	bool ran;
-	int r;
+	int map_fd, fd;
 
 	if (gen_loader_fixture_init(&f) == 0) {
 		/*
-		 * Correct blob but a non-exclusive metadata map: the verifier does
-		 * not reject (excl_prog_sha unset), so the runtime map->excl == 1
-		 * check in the loader must.
+		 * A signed program may only bind exclusive maps through fd_array
+		 * (their contents are folded into the signature). Binding a
+		 * non-exclusive map is rejected, before the signature is even
+		 * examined.
 		 */
-		r = run_gen_loader(f.gopts.insns, f.gopts.insns_sz, f.blob,
-				   f.data_sz, NULL, 0, NULL, 0, true, f.ctx,
-				   f.ctx_sz, &ran);
-		ASSERT_TRUE(ran, "loader ran");
-		ASSERT_EQ(r, -EINVAL, "non-exclusive metadata map rejected");
+		map_fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, "nonexcl", 4,
+					f.data_sz, 1, NULL);
+		if (ASSERT_OK_FD(map_fd, "nonexcl_map")) {
+			if (ASSERT_OK(bpf_map_freeze(map_fd), "freeze")) {
+				fd = load_loader(f.gopts.insns, f.gopts.insns_sz,
+						 map_fd, junk, sizeof(junk),
+						 KEY_SPEC_SESSION_KEYRING, 1);
+				ASSERT_EQ(fd, -EPERM,
+					  "non-exclusive map in signed fd_array rejected");
+				if (fd >= 0)
+					close(fd);
+			}
+			close(map_fd);
+		}
 	}
 	gen_loader_fixture_fini(&f);
 }
 
-static void metadata_hash_not_computed(void)
+static void signed_unfrozen_fd_array_rejected(void)
 {
+	static const __u8 junk[64] = { 0x30, 0x42, 0x13, 0x37, };
+	LIBBPF_OPTS(bpf_map_create_opts, mopts);
 	struct gen_loader_fixture f;
-	bool ran;
-	int r;
+	__u32 key = 0;
+	int map_fd, fd;
 
 	if (gen_loader_fixture_init(&f) == 0) {
 		/*
-		 * Correct, exclusive, frozen map, but its hash was never computed
-		 * (no OBJ_GET_INFO_BY_FD), so map->sha stays zero. The loader must
-		 * fail closed rather than treat an unset hash as a match.
+		 * The metadata map must be frozen before a signed load so the
+		 * folded bytes cannot change afterwards. Bind an exclusive map
+		 * with matching contents but skip the freeze: the load must be
+		 * rejected by the frozen check with -EPERM. The exclusivity
+		 * check right after it would pass, so the errno uniquely pins
+		 * the freeze requirement.
 		 */
-		r = run_gen_loader(f.gopts.insns, f.gopts.insns_sz, f.blob,
-				   f.data_sz, f.excl, sizeof(f.excl), NULL, 0,
-				   false, f.ctx, f.ctx_sz, &ran);
-		ASSERT_TRUE(ran, "loader ran");
-		ASSERT_EQ(r, -EINVAL, "uncomputed metadata hash rejected");
+		mopts.excl_prog_hash = f.excl;
+		mopts.excl_prog_hash_size = sizeof(f.excl);
+		map_fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, "unfrozen", 4,
+					f.data_sz, 1, &mopts);
+		if (ASSERT_OK_FD(map_fd, "unfrozen_map")) {
+			if (ASSERT_OK(bpf_map_update_elem(map_fd, &key, f.blob, 0),
+				      "update")) {
+				fd = load_loader(f.gopts.insns, f.gopts.insns_sz,
+						 map_fd, junk, sizeof(junk),
+						 KEY_SPEC_SESSION_KEYRING, 1);
+				ASSERT_EQ(fd, -EPERM,
+					  "unfrozen map in signed fd_array rejected");
+				if (fd >= 0)
+					close(fd);
+			}
+			close(map_fd);
+		}
 	}
 	gen_loader_fixture_fini(&f);
 }
 
-static void signature_enforced(void)
+static void signed_nonarray_fd_array_rejected(void)
 {
 	static const __u8 junk[64] = { 0x30, 0x42, 0x13, 0x37, };
+	LIBBPF_OPTS(bpf_map_create_opts, mopts);
 	struct gen_loader_fixture f;
+	int map_fd, fd;
+
+	if (gen_loader_fixture_init(&f) == 0) {
+		/*
+		 * Only a plain BPF_MAP_TYPE_ARRAY may be folded into the
+		 * signature. An exclusive map of any other type is rejected
+		 * (-EINVAL) rather than folded - this is the type gate that
+		 * keeps arena maps (map_direct_value_addr() returns a user
+		 * address) and insn-array maps (buffer smaller than value_size)
+		 * out of the hashed region, where the old code would have
+		 * memcpy()'d from them. A hash map stands in here: it is
+		 * exclusive (bound to the loader digest) but not an array.
+		 */
+		mopts.excl_prog_hash = f.excl;
+		mopts.excl_prog_hash_size = sizeof(f.excl);
+		map_fd = bpf_map_create(BPF_MAP_TYPE_HASH, "excl_hash", 4, 4, 1,
+					&mopts);
+		if (ASSERT_OK_FD(map_fd, "excl_hash_map")) {
+			fd = load_loader(f.gopts.insns, f.gopts.insns_sz, map_fd,
+					 junk, sizeof(junk),
+					 KEY_SPEC_SESSION_KEYRING, 1);
+			ASSERT_EQ(fd, -EINVAL,
+				  "non-array map in signed fd_array rejected");
+			if (fd >= 0)
+				close(fd);
+			close(map_fd);
+		}
+	}
+	gen_loader_fixture_fini(&f);
+}
+
+static int setup_meta_map(const struct gen_loader_fixture *f);
+
+static void signed_btf_fd_array_rejected(void)
+{
+	char dir_tmpl[] = "/tmp/signed_loader_btfXXXXXX", *dir = NULL;
+	__u32 sig_sz = 8192;
+	int map_fd = -1, prog_fd = -1;
+	unsigned char *buf = NULL;
+	struct gen_loader_fixture f;
+	bool have_fixture = false;
+	struct btf *btf = NULL;
+	union bpf_attr attr;
+	int fds[2];
+	__u8 sig[8192];
+
+	syscall(__NR_request_key, "keyring", "_uid.0", NULL,
+		KEY_SPEC_SESSION_KEYRING);
+	dir = mkdtemp(dir_tmpl);
+	if (!ASSERT_OK_PTR(dir, "mkdtemp"))
+		return;
+	if (!ASSERT_OK(run_setup("setup", dir), "verify_sig_setup")) {
+		rmdir(dir);
+		return;
+	}
+	have_fixture = true;
+	if (gen_loader_fixture_init(&f) != 0)
+		goto out;
+
+	/*
+	 * fd_array binds maps and BTFs alike, but only exclusive array maps are
+	 * folded into the signature. Build an otherwise genuinely signed load -
+	 * insns || metadata, exclusive frozen map at fd_array[0] - then smuggle
+	 * an extra BTF into fd_array[1]. A signed program may not bind any BTF,
+	 * so resolving the fd_array entries rejects the BTF with -EACCES (in
+	 * __add_used_btf(), before the signature is even verified).
+	 */
+	buf = malloc((size_t)f.gopts.insns_sz + f.data_sz);
+	if (!ASSERT_OK_PTR(buf, "signbuf"))
+		goto out;
+	memcpy(buf, f.gopts.insns, f.gopts.insns_sz);
+	memcpy(buf + f.gopts.insns_sz, f.blob, f.data_sz);
+	if (!ASSERT_OK(sign_buf(dir, buf, f.gopts.insns_sz + f.data_sz, sig,
+			       &sig_sz), "sign insns||metadata"))
+		goto out;
+
+	map_fd = setup_meta_map(&f);
+	if (!ASSERT_OK_FD(map_fd, "meta_map"))
+		goto out;
+	btf = btf__new_empty();
+	if (!ASSERT_OK_PTR(btf, "btf_new_empty"))
+		goto out;
+	btf__add_int(btf, "int", 4, BTF_INT_SIGNED);
+	if (!ASSERT_OK(btf__load_into_kernel(btf), "btf_load"))
+		goto out;
+
+	fds[0] = map_fd;
+	fds[1] = btf__fd(btf);
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_type = BPF_PROG_TYPE_SYSCALL;
+	attr.insns = ptr_to_u64(f.gopts.insns);
+	attr.insn_cnt = f.gopts.insns_sz / sizeof(struct bpf_insn);
+	attr.license = ptr_to_u64("Dual BSD/GPL");
+	attr.prog_flags = BPF_F_SLEEPABLE;
+	attr.fd_array = ptr_to_u64(fds);
+	attr.fd_array_cnt = 2;
+	attr.signature = ptr_to_u64(sig);
+	attr.signature_size = sig_sz;
+	attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
+	memcpy(attr.prog_name, "__loader.prog", sizeof("__loader.prog"));
+	prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
+			  offsetofend(union bpf_attr, keyring_id));
+	ASSERT_EQ(prog_fd < 0 ? -errno : prog_fd, -EACCES,
+		  "BTF in signed fd_array rejected");
+	if (prog_fd >= 0)
+		close(prog_fd);
+out:
+	if (btf)
+		btf__free(btf);
+	if (map_fd >= 0)
+		close(map_fd);
+	if (have_fixture)
+		gen_loader_fixture_fini(&f);
+	if (dir)
+		run_setup("cleanup", dir);
+	free(buf);
+}
+
+static void signature_failure_logs(void)
+{
+	static const __u8 junk[64] = { 0x30, 0x42, 0x13, 0x37, };
+	char log_buf[1024] = {};
+	struct gen_loader_fixture f;
+	union bpf_attr attr;
 	int fd;
 
 	if (gen_loader_fixture_init(&f) == 0) {
 		/*
-		 * A present-but-invalid signature (the cert bytes are not a
-		 * PKCS#7 signature) must be rejected at load: the signature
-		 * path is honored, not ignored. (The valid path is covered by
-		 * the signed lskels.)
+		 * Signature verification now runs inside bpf_check(), so a
+		 * failure is reported through the verifier log. A present-but-
+		 * invalid signature is rejected and the log says why.
 		 */
-		fd = load_loader(f.gopts.insns, f.gopts.insns_sz, -1, junk,
-				 sizeof(junk), KEY_SPEC_SESSION_KEYRING);
+		memset(&attr, 0, sizeof(attr));
+		attr.prog_type = BPF_PROG_TYPE_SYSCALL;
+		attr.insns = ptr_to_u64(f.gopts.insns);
+		attr.insn_cnt = f.gopts.insns_sz / sizeof(struct bpf_insn);
+		attr.license = ptr_to_u64("Dual BSD/GPL");
+		attr.prog_flags = BPF_F_SLEEPABLE;
+		attr.signature = ptr_to_u64(junk);
+		attr.signature_size = sizeof(junk);
+		attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
+		attr.log_level = 1;
+		attr.log_buf = ptr_to_u64(log_buf);
+		attr.log_size = sizeof(log_buf);
+		memcpy(attr.prog_name, "__loader.prog", sizeof("__loader.prog"));
+
+		fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
+			     offsetofend(union bpf_attr, keyring_id));
 		ASSERT_LT(fd, 0, "invalid signature rejected at load");
+		if (fd >= 0)
+			close(fd);
+		ASSERT_HAS_SUBSTR(log_buf, "signature verification failed",
+				  "verifier logs signature failure");
 	}
 	gen_loader_fixture_fini(&f);
 }
@@ -495,7 +573,7 @@ static void signature_too_large(void)
 		 * is rejected before the buffer is read.
 		 */
 		fd = load_loader(f.gopts.insns, f.gopts.insns_sz, -1, junk,
-				 64 << 20, KEY_SPEC_SESSION_KEYRING);
+				 64 << 20, KEY_SPEC_SESSION_KEYRING, 0);
 		ASSERT_EQ(fd, -EINVAL, "oversized signature rejected");
 	}
 	gen_loader_fixture_fini(&f);
@@ -515,7 +593,7 @@ static void signature_bad_keyring(void)
 		 * large positive serial takes the user-keyring path and won't exist.
 		 */
 		fd = load_loader(f.gopts.insns, f.gopts.insns_sz, -1, junk,
-				 sizeof(junk), INT_MAX);
+				 sizeof(junk), INT_MAX, 0);
 		ASSERT_EQ(fd, -EINVAL, "signature with bad keyring_id rejected");
 	}
 	gen_loader_fixture_fini(&f);
@@ -575,7 +653,7 @@ static void metadata_ctx_max_entries_ignored(void)
 	memcpy(blob, gopts.data, data_sz);
 
 	r = run_gen_loader(gopts.insns, gopts.insns_sz, blob, data_sz,
-			   excl, sizeof(excl), NULL, 0, true, ctx, ctx_sz, &ran);
+			   excl, sizeof(excl), NULL, 0, ctx, ctx_sz, &ran);
 	if (!ASSERT_TRUE(ran, "loader ran") ||
 	    !ASSERT_EQ(r, 0, "loader retval"))
 		goto free_blob;
@@ -661,7 +739,7 @@ static void metadata_ctx_initial_value_ignored(void)
 	memcpy(blob, gopts.data, data_sz);
 
 	r = run_gen_loader(gopts.insns, gopts.insns_sz, blob, data_sz,
-			   excl, sizeof(excl), NULL, 0, true, ctx, ctx_sz, &ran);
+			   excl, sizeof(excl), NULL, 0, ctx, ctx_sz, &ran);
 	if (!ASSERT_TRUE(ran, "loader ran") ||
 	    !ASSERT_EQ(r, 0, "loader retval"))
 		goto free_blob;
@@ -714,6 +792,7 @@ static void signature_authenticates_insns(void)
 	__u8 excl[SHA256_DIGEST_LENGTH], sig[8192];
 	__u32 sig_sz = sizeof(sig), insns_sz, data_sz, ctx_sz;
 	unsigned char *insns = NULL, *tampered = NULL, *blob = NULL;
+	unsigned char *signbuf = NULL;
 	int nr_maps = 0, nr_progs = 0, r;
 	struct bpf_program *p;
 	struct bpf_map *m;
@@ -760,29 +839,141 @@ static void signature_authenticates_insns(void)
 	memcpy(blob, gopts.data, data_sz);
 	libbpf_sha256(insns, insns_sz, excl);
 
-	if (!ASSERT_OK(sign_buf(dir, insns, insns_sz, sig, &sig_sz), "sign-file"))
+	signbuf = malloc((size_t)insns_sz + data_sz);
+	if (!ASSERT_OK_PTR(signbuf, "signbuf"))
+		goto cleanup;
+	memcpy(signbuf, insns, insns_sz);
+	memcpy(signbuf + insns_sz, blob, data_sz);
+	if (!ASSERT_OK(sign_buf(dir, signbuf, insns_sz + data_sz, sig, &sig_sz),
+		       "sign-file"))
 		goto cleanup;
 
 	memset(ctx, 0, ctx_sz);
 	((struct bpf_loader_ctx *)ctx)->sz = ctx_sz;
 	r = run_gen_loader(insns, insns_sz, blob, data_sz, excl, sizeof(excl),
-			   sig, sig_sz, true, ctx, ctx_sz, &ran);
+			   sig, sig_sz, ctx, ctx_sz, &ran);
 	ASSERT_TRUE(ran, "valid signature: loader loaded and ran");
 	ASSERT_EQ(r, 0, "valid signature accepted");
 	close_loader_ctx_fds(ctx, nr_maps, nr_progs);
 
 	memcpy(tampered, insns, insns_sz);
 	tampered[insns_sz / 2] ^= 0xff;
+	/*
+	 * Bind the metadata map to the tampered loader's own digest, so the
+	 * verifier's exclusive-map check (excl_prog_sha == prog->digest) passes
+	 * and the signature - verified after the maps are resolved - is what
+	 * rejects the load. This is the attacker's best case: even after
+	 * re-binding the exclusive map to their tampered loader, the signature
+	 * over the original insns || metadata still fails. (Leaving the map
+	 * bound to the original digest would instead trip the excl check first.)
+	 */
+	libbpf_sha256(tampered, insns_sz, excl);
 	memset(ctx, 0, ctx_sz);
 	((struct bpf_loader_ctx *)ctx)->sz = ctx_sz;
 	r = run_gen_loader(tampered, insns_sz, blob, data_sz, excl, sizeof(excl),
-			   sig, sig_sz, true, ctx, ctx_sz, &ran);
+			   sig, sig_sz, ctx, ctx_sz, &ran);
 	ASSERT_FALSE(ran, "tampered loader rejected before run");
 	ASSERT_EQ(r, -EKEYREJECTED, "signature is bound to the instructions");
 cleanup:
 	free(insns);
 	free(tampered);
 	free(blob);
+	free(signbuf);
+	free(ctx);
+	test_signed_loader__destroy(skel);
+	run_setup("cleanup", dir);
+}
+
+static void signature_authenticates_metadata(void)
+{
+	LIBBPF_OPTS(gen_loader_opts, gopts, .gen_hash = true);
+	char dir_tmpl[] = "/tmp/signed_loaderXXXXXX", *dir;
+	struct test_signed_loader *skel = NULL;
+	__u8 excl[SHA256_DIGEST_LENGTH], sig[8192];
+	__u32 sig_sz = sizeof(sig), insns_sz, data_sz, ctx_sz;
+	unsigned char *insns = NULL, *blob = NULL;
+	unsigned char *signbuf = NULL;
+	int nr_maps = 0, nr_progs = 0, r;
+	struct bpf_program *p;
+	struct bpf_map *m;
+	void *ctx = NULL;
+	bool ran;
+
+	syscall(__NR_request_key, "keyring", "_uid.0", NULL,
+		KEY_SPEC_SESSION_KEYRING);
+	dir = mkdtemp(dir_tmpl);
+	if (!ASSERT_OK_PTR(dir, "mkdtemp"))
+		return;
+	if (!ASSERT_OK(run_setup("setup", dir), "verify_sig_setup")) {
+		rmdir(dir);
+		return;
+	}
+
+	skel = test_signed_loader__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		goto cleanup;
+	if (!ASSERT_OK(bpf_object__gen_loader(skel->obj, &gopts), "gen_loader"))
+		goto cleanup;
+	if (!ASSERT_OK(bpf_object__load(skel->obj), "gen_load"))
+		goto cleanup;
+
+	bpf_object__for_each_program(p, skel->obj)
+		nr_progs++;
+	bpf_object__for_each_map(m, skel->obj)
+		nr_maps++;
+	ctx_sz = sizeof(struct bpf_loader_ctx) +
+		 nr_maps * sizeof(struct bpf_map_desc) +
+		 nr_progs * sizeof(struct bpf_prog_desc);
+	insns_sz = gopts.insns_sz;
+	data_sz = gopts.data_sz;
+	ctx = calloc(1, ctx_sz);
+	insns = malloc(insns_sz);
+	blob = malloc(data_sz);
+	if (!ASSERT_OK_PTR(ctx, "ctx") ||
+	    !ASSERT_OK_PTR(insns, "insns") ||
+	    !ASSERT_OK_PTR(blob, "blob"))
+		goto cleanup;
+	memcpy(insns, gopts.insns, insns_sz);
+	memcpy(blob, gopts.data, data_sz);
+	libbpf_sha256(insns, insns_sz, excl);
+
+	signbuf = malloc((size_t)insns_sz + data_sz);
+	if (!ASSERT_OK_PTR(signbuf, "signbuf"))
+		goto cleanup;
+	memcpy(signbuf, insns, insns_sz);
+	memcpy(signbuf + insns_sz, blob, data_sz);
+	if (!ASSERT_OK(sign_buf(dir, signbuf, insns_sz + data_sz, sig, &sig_sz),
+		       "sign-file"))
+		goto cleanup;
+
+	memset(ctx, 0, ctx_sz);
+	((struct bpf_loader_ctx *)ctx)->sz = ctx_sz;
+	r = run_gen_loader(insns, insns_sz, blob, data_sz, excl, sizeof(excl),
+			   sig, sig_sz, ctx, ctx_sz, &ran);
+	ASSERT_TRUE(ran, "valid signature: loader loaded and ran");
+	ASSERT_EQ(r, 0, "valid signature accepted");
+	close_loader_ctx_fds(ctx, nr_maps, nr_progs);
+
+	/*
+	 * Tamper the metadata after signing while leaving the instructions
+	 * and thus the exclusive hash binding untouched: the map freezes
+	 * fine and excl_prog_sha still matches the loader's digest, so the
+	 * load reaches signature verification, which folds the live frozen
+	 * map bytes into the checked payload and must reject the modified
+	 * blob. A kernel folding anything but the map contents themselves
+	 * would wrongly accept this load.
+	 */
+	blob[data_sz / 2] ^= 0xff;
+	memset(ctx, 0, ctx_sz);
+	((struct bpf_loader_ctx *)ctx)->sz = ctx_sz;
+	r = run_gen_loader(insns, insns_sz, blob, data_sz, excl, sizeof(excl),
+			   sig, sig_sz, ctx, ctx_sz, &ran);
+	ASSERT_FALSE(ran, "tampered metadata rejected before run");
+	ASSERT_EQ(r, -EKEYREJECTED, "signature is bound to the metadata");
+cleanup:
+	free(insns);
+	free(blob);
+	free(signbuf);
 	free(ctx);
 	test_signed_loader__destroy(skel);
 	run_setup("cleanup", dir);
@@ -1007,10 +1198,11 @@ static void lsm_signature_verdict(void)
 {
 	char dir_tmpl[] = "/tmp/signed_loader_lsmXXXXXX", *dir = NULL;
 	struct test_signed_loader_lsm *lsm = NULL;
+	__u32 sig_sz = 8192, msig_sz = 8192;
 	int map_fd = -1, prog_fd = -1;
 	bool have_fixture = false;
 	struct gen_loader_fixture f;
-	__u32 sig_sz = 8192;
+	unsigned char *buf;
 	__s32 ses_serial;
 	__u8 sig[8192];
 
@@ -1029,7 +1221,7 @@ static void lsm_signature_verdict(void)
 	if (!ASSERT_OK_FD(map_fd, "meta_map_unsigned"))
 		goto out;
 	lsm->bss->seen = 0;
-	prog_fd = load_loader(f.gopts.insns, f.gopts.insns_sz, map_fd, NULL, 0, 0);
+	prog_fd = load_loader(f.gopts.insns, f.gopts.insns_sz, map_fd, NULL, 0, 0, 0);
 	close(map_fd);
 	map_fd = -1;
 	if (!ASSERT_OK_FD(prog_fd, "unsigned loader load"))
@@ -1062,22 +1254,51 @@ static void lsm_signature_verdict(void)
 		goto out;
 	lsm->bss->seen = 0;
 	prog_fd = load_loader(f.gopts.insns, f.gopts.insns_sz, map_fd, sig,
-			      sig_sz, KEY_SPEC_SESSION_KEYRING);
+			      sig_sz, KEY_SPEC_SESSION_KEYRING, 0);
 	close(map_fd);
 	map_fd = -1;
-	if (!ASSERT_OK_FD(prog_fd, "signed loader load"))
-		goto out;
-	close(prog_fd);
+	ASSERT_EQ(prog_fd, -EACCES, "unfolded metadata rejected");
+	if (prog_fd >= 0)
+		close(prog_fd);
 	prog_fd = -1;
 
 	ses_serial = syscall(__NR_keyctl, KEYCTL_GET_KEYRING_ID,
 			     KEY_SPEC_SESSION_KEYRING, 0);
 	ASSERT_EQ(lsm->bss->seen, 1, "signed: one observed load");
-	ASSERT_EQ(lsm->bss->sig_verdict, BPF_SIG_VERIFIED, "signed verdict");
+	ASSERT_EQ(lsm->bss->sig_verdict, BPF_SIG_VERIFIED,
+		  "admission saw a valid signature");
 	ASSERT_EQ(lsm->bss->sig_keyring_type, BPF_SIG_KEYRING_USER, "signed keyring type");
 	ASSERT_GT(ses_serial, 0, "session keyring serial resolved");
 	ASSERT_EQ(lsm->bss->sig_keyring_serial, ses_serial,
 		  "signed: validated against session keyring");
+
+	buf = malloc((size_t)f.gopts.insns_sz + f.data_sz);
+	if (!ASSERT_OK_PTR(buf, "meta_signbuf"))
+		goto out;
+	memcpy(buf, f.gopts.insns, f.gopts.insns_sz);
+	memcpy(buf + f.gopts.insns_sz, f.blob, f.data_sz);
+	if (!ASSERT_OK(sign_buf(dir, buf, f.gopts.insns_sz + f.data_sz,
+				sig, &msig_sz), "sign insns||metadata")) {
+		free(buf);
+		goto out;
+	}
+	free(buf);
+
+	map_fd = setup_meta_map(&f);
+	if (!ASSERT_OK_FD(map_fd, "meta_map_bound"))
+		goto out;
+	lsm->bss->seen = 0;
+	prog_fd = load_loader(f.gopts.insns, f.gopts.insns_sz, map_fd, sig,
+			      msig_sz, KEY_SPEC_SESSION_KEYRING, 1);
+	close(map_fd);
+	map_fd = -1;
+	if (!ASSERT_OK_FD(prog_fd, "metadata-bound loader load"))
+		goto out;
+	close(prog_fd);
+	prog_fd = -1;
+	ASSERT_EQ(lsm->bss->seen, 1, "metadata: one observed load");
+	ASSERT_EQ(lsm->bss->sig_verdict, BPF_SIG_VERIFIED,
+		  "metadata-bound verdict");
 out:
 	if (map_fd >= 0)
 		close(map_fd);
@@ -1090,20 +1311,467 @@ static void lsm_signature_verdict(void)
 	test_signed_loader_lsm__destroy(lsm);
 }
 
+/*
+ * Load-time metadata verification: the kernel folds the frozen metadata map
+ * into the signature (insns || metadata) and checks it at BPF_PROG_LOAD via
+ * fd_array_cnt, rather than the loader checking from within BPF. Sign that
+ * concatenation, hand the kernel the map, and confirm the signed loader loads,
+ * runs, and installs its target.
+ */
+static int loadtime_drive(const char *dir, const void *insns, __u32 insns_sz,
+			  const void *data, __u32 data_sz, const __u8 *excl,
+			  void *ctx, __u32 ctx_sz, int *load_ret, bool *ran)
+{
+	LIBBPF_OPTS(bpf_map_create_opts, mopts,
+		    .excl_prog_hash = excl,
+		    .excl_prog_hash_size = SHA256_DIGEST_LENGTH);
+	__u32 sig_sz = 8192, key = 0;
+	unsigned char *buf = NULL;
+	int map_fd, prog_fd, ret = 0;
+	union bpf_attr attr;
+	__u8 sig[8192];
+
+	*ran = false;
+	*load_ret = 0;
+
+	/*
+	 * Metadata map, bound to the loader digest and frozen, exactly as
+	 * skel_internal.h's bpf_load_and_run() sets it up.
+	 */
+	map_fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, "__loader.map", 4,
+				data_sz, 1, &mopts);
+	if (map_fd < 0) {
+		ret = -errno;
+		goto out_load;
+	}
+	if (bpf_map_update_elem(map_fd, &key, data, 0) || bpf_map_freeze(map_fd)) {
+		ret = -errno;
+		goto out_load;
+	}
+
+	/* Sign insns || metadata, the same bytes the kernel reconstructs. */
+	buf = malloc((size_t)insns_sz + data_sz);
+	if (!buf) {
+		ret = -ENOMEM;
+		goto out_load;
+	}
+	memcpy(buf, insns, insns_sz);
+	memcpy(buf + insns_sz, data, data_sz);
+	ret = sign_buf(dir, buf, insns_sz + data_sz, sig, &sig_sz);
+	if (ret)
+		goto out_load;
+
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_type = BPF_PROG_TYPE_SYSCALL;
+	attr.insns = ptr_to_u64(insns);
+	attr.insn_cnt = insns_sz / sizeof(struct bpf_insn);
+	attr.license = ptr_to_u64("Dual BSD/GPL");
+	attr.prog_flags = BPF_F_SLEEPABLE;
+	attr.fd_array = ptr_to_u64(&map_fd);
+	attr.signature = ptr_to_u64(sig);
+	attr.signature_size = sig_sz;
+	attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
+	attr.fd_array_cnt = 1;
+	memcpy(attr.prog_name, "__loader.prog", sizeof("__loader.prog"));
+	prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
+			  offsetofend(union bpf_attr, keyring_id));
+	if (prog_fd < 0) {
+		ret = -errno;
+		goto out_load;
+	}
+
+	memset(&attr, 0, sizeof(attr));
+	attr.test.prog_fd = prog_fd;
+	attr.test.ctx_in = ptr_to_u64(ctx);
+	attr.test.ctx_size_in = ctx_sz;
+	if (syscall(__NR_bpf, BPF_PROG_RUN, &attr,
+		    offsetofend(union bpf_attr, test)) < 0) {
+		ret = -errno;
+		goto out_prog;
+	}
+	*ran = true;
+	ret = (int)attr.test.retval;
+out_prog:
+	close(prog_fd);
+	goto out_map;
+out_load:
+	*load_ret = ret;
+out_map:
+	free(buf);
+	if (map_fd >= 0)
+		close(map_fd);
+	return ret;
+}
+
+static void loadtime_verify(struct bpf_object *obj, int expect_maps)
+{
+	LIBBPF_OPTS(gen_loader_opts, gopts, .gen_hash = true);
+	char dir_tmpl[] = "/tmp/signed_loader_ltXXXXXX", *dir = NULL;
+	int nr_maps = 0, nr_progs = 0, load_ret = 0, r;
+	__u8 excl[SHA256_DIGEST_LENGTH];
+	struct bpf_prog_desc *pd;
+	struct bpf_map_desc *md;
+	unsigned char *blob = NULL;
+	struct bpf_program *p;
+	struct bpf_map *m;
+	__u32 ctx_sz, data_sz;
+	void *ctx = NULL;
+	bool ran = false;
+
+	syscall(__NR_request_key, "keyring", "_uid.0", NULL,
+		KEY_SPEC_SESSION_KEYRING);
+	dir = mkdtemp(dir_tmpl);
+	if (!ASSERT_OK_PTR(dir, "mkdtemp"))
+		return;
+	if (!ASSERT_OK(run_setup("setup", dir), "verify_sig_setup")) {
+		rmdir(dir);
+		return;
+	}
+
+	if (!ASSERT_OK(bpf_object__gen_loader(obj, &gopts), "gen_loader"))
+		goto out;
+	if (!ASSERT_OK(bpf_object__load(obj), "gen_load"))
+		goto out;
+
+	bpf_object__for_each_program(p, obj)
+		nr_progs++;
+	bpf_object__for_each_map(m, obj)
+		nr_maps++;
+	if (!ASSERT_EQ(nr_maps, expect_maps, "fixture map count"))
+		goto out;
+
+	ctx_sz = sizeof(struct bpf_loader_ctx) +
+		 nr_maps * sizeof(struct bpf_map_desc) +
+		 nr_progs * sizeof(struct bpf_prog_desc);
+	ctx = calloc(1, ctx_sz);
+	if (!ASSERT_OK_PTR(ctx, "ctx_alloc"))
+		goto out;
+	((struct bpf_loader_ctx *)ctx)->sz = ctx_sz;
+
+	data_sz = gopts.data_sz;
+	blob = malloc(data_sz);
+	if (!ASSERT_OK_PTR(blob, "blob_alloc"))
+		goto out;
+	memcpy(blob, gopts.data, data_sz);
+
+	/* excl_prog_hash = SHA256(loader insns) == the loader's prog->digest. */
+	libbpf_sha256(gopts.insns, gopts.insns_sz, excl);
+
+	r = loadtime_drive(dir, gopts.insns, gopts.insns_sz, blob, data_sz,
+			   excl, ctx, ctx_sz, &load_ret, &ran);
+	ASSERT_OK(load_ret, "signed loader loaded (insns || metadata)");
+	ASSERT_TRUE(ran, "loader ran");
+	ASSERT_EQ(r, 0, "loader installed its target");
+
+	md = (struct bpf_map_desc *)((char *)ctx + sizeof(struct bpf_loader_ctx));
+	pd = (struct bpf_prog_desc *)(md + nr_maps);
+	ASSERT_GT(pd[0].prog_fd, 0, "target program installed");
+	if (nr_maps)
+		ASSERT_GT(md[0].map_fd, 0, "target map installed");
+
+	close_loader_ctx_fds(ctx, nr_maps, nr_progs);
+out:
+	free(blob);
+	free(ctx);
+	if (dir)
+		run_setup("cleanup", dir);
+}
+
+static void loadtime_no_map(void)
+{
+	struct test_signed_loader *skel = test_signed_loader__open();
+
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+	loadtime_verify(skel->obj, 0);
+	test_signed_loader__destroy(skel);
+}
+
+static void loadtime_with_map(void)
+{
+	struct test_signed_loader_map *skel = test_signed_loader_map__open();
+
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+	loadtime_verify(skel->obj, 1);
+	test_signed_loader_map__destroy(skel);
+}
+
+/*
+ * A signed program need not bind any map. A plain BPF_PROG_TYPE_SYSCALL
+ * program with no fd_array is signed over its instructions alone: the kernel
+ * verifies the signature, folds no metadata, and the program loads. Exercise
+ * the fd_array == NULL / fd_array_cnt == 0 path, and confirm the signature
+ * still authenticates the instructions (a tampered copy is rejected).
+ */
+static void signed_no_fd_array(void)
+{
+	struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	char dir_tmpl[] = "/tmp/signed_loaderXXXXXX", *dir;
+	__u32 sig_sz = 8192;
+	union bpf_attr attr;
+	__u8 sig[8192];
+	int prog_fd, err;
+
+	syscall(__NR_request_key, "keyring", "_uid.0", NULL,
+		KEY_SPEC_SESSION_KEYRING);
+	dir = mkdtemp(dir_tmpl);
+	if (!ASSERT_OK_PTR(dir, "mkdtemp"))
+		return;
+	if (!ASSERT_OK(run_setup("setup", dir), "verify_sig_setup")) {
+		rmdir(dir);
+		return;
+	}
+
+	/* No metadata map: the signed payload is the instructions alone. */
+	if (!ASSERT_OK(sign_buf(dir, insns, sizeof(insns), sig, &sig_sz),
+		       "sign-file"))
+		goto cleanup;
+
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_type = BPF_PROG_TYPE_SYSCALL;
+	attr.insns = ptr_to_u64(insns);
+	attr.insn_cnt = ARRAY_SIZE(insns);
+	attr.license = ptr_to_u64("Dual BSD/GPL");
+	attr.prog_flags = BPF_F_SLEEPABLE;
+	attr.signature = ptr_to_u64(sig);
+	attr.signature_size = sig_sz;
+	attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
+	/* fd_array and fd_array_cnt deliberately left NULL/0. */
+	memcpy(attr.prog_name, "signed_nomap", sizeof("signed_nomap"));
+
+	prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
+			  offsetofend(union bpf_attr, keyring_id));
+	if (!ASSERT_GE(prog_fd, 0, "map-less signed program loaded")) {
+		if (prog_fd >= 0)
+			close(prog_fd);
+		goto cleanup;
+	}
+	close(prog_fd);
+
+	/* The signature covers the instructions, so tampering must be rejected. */
+	insns[0].imm = 1;
+	prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
+			  offsetofend(union bpf_attr, keyring_id));
+	err = prog_fd < 0 ? -errno : prog_fd;
+	ASSERT_EQ(err, -EKEYREJECTED, "tampered map-less program rejected");
+	if (prog_fd >= 0)
+		close(prog_fd);
+cleanup:
+	run_setup("cleanup", dir);
+}
+
+/*
+ * A signed program may reach maps only through fd_array indices, so the kernel
+ * folds (and thus attests) them. A direct BPF_PSEUDO_MAP_FD reference - a raw,
+ * unfolded fd baked into the signed instructions - is rejected by the verifier.
+ */
+static void signed_map_by_fd_rejected(void)
+{
+	struct bpf_insn insns[] = {
+		BPF_LD_MAP_FD(BPF_REG_1, 0),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	char dir_tmpl[] = "/tmp/signed_loaderXXXXXX", *dir;
+	__u32 sig_sz = 8192;
+	union bpf_attr attr;
+	__u8 sig[8192];
+	int map_fd, prog_fd, err;
+
+	map_fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, "sig_mapfd", 4, 4, 1, NULL);
+	if (!ASSERT_GE(map_fd, 0, "map_create"))
+		return;
+	insns[0].imm = map_fd;	/* bake the raw map fd into the ld_imm64 */
+
+	syscall(__NR_request_key, "keyring", "_uid.0", NULL,
+		KEY_SPEC_SESSION_KEYRING);
+	dir = mkdtemp(dir_tmpl);
+	if (!ASSERT_OK_PTR(dir, "mkdtemp"))
+		goto out_map;
+	if (!ASSERT_OK(run_setup("setup", dir), "verify_sig_setup")) {
+		rmdir(dir);
+		goto out_map;
+	}
+
+	/* Sign the instructions, raw map fd and all. */
+	if (!ASSERT_OK(sign_buf(dir, insns, sizeof(insns), sig, &sig_sz),
+		       "sign-file"))
+		goto cleanup;
+
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_type = BPF_PROG_TYPE_SYSCALL;
+	attr.insns = ptr_to_u64(insns);
+	attr.insn_cnt = ARRAY_SIZE(insns);
+	attr.license = ptr_to_u64("Dual BSD/GPL");
+	attr.prog_flags = BPF_F_SLEEPABLE;
+	attr.signature = ptr_to_u64(sig);
+	attr.signature_size = sig_sz;
+	attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
+	/* No fd_array: the map is reached by a raw fd in the instructions. */
+	memcpy(attr.prog_name, "signed_mapfd", sizeof("signed_mapfd"));
+
+	prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
+			  offsetofend(union bpf_attr, keyring_id));
+	err = prog_fd < 0 ? -errno : prog_fd;
+	ASSERT_EQ(err, -EINVAL, "signed program referencing a map by fd rejected");
+	if (prog_fd >= 0)
+		close(prog_fd);
+cleanup:
+	run_setup("cleanup", dir);
+out_map:
+	close(map_fd);
+}
+
+/*
+ * A signed program may reach maps only through the continuous fd_array, so the
+ * kernel folds (and thus attests) them. Referencing a map by fd_array *index*
+ * while leaving fd_array_cnt at 0 selects the sparse path, which resolves a map
+ * the signature never covered; the verifier rejects it up front with -EACCES.
+ */
+static void signed_sparse_fd_array_rejected(void)
+{
+	struct bpf_insn insns[] = {
+		BPF_LD_IMM64_RAW(BPF_REG_1, BPF_PSEUDO_MAP_IDX, 0),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	char dir_tmpl[] = "/tmp/signed_loader_spXXXXXX", *dir;
+	__u32 sig_sz = 8192;
+	union bpf_attr attr;
+	__u8 sig[8192];
+	int map_fd, prog_fd, err;
+
+	map_fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, "sig_sparse", 4, 4, 1, NULL);
+	if (!ASSERT_GE(map_fd, 0, "map_create"))
+		return;
+
+	syscall(__NR_request_key, "keyring", "_uid.0", NULL,
+		KEY_SPEC_SESSION_KEYRING);
+	dir = mkdtemp(dir_tmpl);
+	if (!ASSERT_OK_PTR(dir, "mkdtemp"))
+		goto out_map;
+	if (!ASSERT_OK(run_setup("setup", dir), "verify_sig_setup")) {
+		rmdir(dir);
+		goto out_map;
+	}
+
+	/* Sign the instructions alone; the sparse map is not folded. */
+	if (!ASSERT_OK(sign_buf(dir, insns, sizeof(insns), sig, &sig_sz),
+		       "sign-file"))
+		goto cleanup;
+
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_type = BPF_PROG_TYPE_SYSCALL;
+	attr.insns = ptr_to_u64(insns);
+	attr.insn_cnt = ARRAY_SIZE(insns);
+	attr.license = ptr_to_u64("Dual BSD/GPL");
+	attr.prog_flags = BPF_F_SLEEPABLE;
+	attr.fd_array = ptr_to_u64(&map_fd);
+	attr.fd_array_cnt = 0; /* sparse: force lazy map resolution */
+	attr.signature = ptr_to_u64(sig);
+	attr.signature_size = sig_sz;
+	attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
+	memcpy(attr.prog_name, "signed_sparse", sizeof("signed_sparse"));
+
+	prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
+			  offsetofend(union bpf_attr, keyring_id));
+	err = prog_fd < 0 ? -errno : prog_fd;
+	ASSERT_EQ(err, -EACCES, "signed program binding a sparse fd_array map rejected");
+	if (prog_fd >= 0)
+		close(prog_fd);
+cleanup:
+	run_setup("cleanup", dir);
+out_map:
+	close(map_fd);
+}
+
+static void signed_module_kfunc_rejected(void)
+{
+	struct bpf_insn insns[] = {
+		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 1, 1),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	char dir_tmpl[] = "/tmp/signed_loader_kfnXXXXXX", *dir;
+	int prog_fd, err, fds[2];
+	struct btf *btf = NULL;
+	__u32 sig_sz = 8192;
+	union bpf_attr attr;
+	__u8 sig[8192];
+
+	syscall(__NR_request_key, "keyring", "_uid.0", NULL,
+		KEY_SPEC_SESSION_KEYRING);
+	dir = mkdtemp(dir_tmpl);
+	if (!ASSERT_OK_PTR(dir, "mkdtemp"))
+		return;
+	if (!ASSERT_OK(run_setup("setup", dir), "verify_sig_setup")) {
+		rmdir(dir);
+		return;
+	}
+	if (!ASSERT_OK(sign_buf(dir, insns, sizeof(insns), sig, &sig_sz),
+		       "sign-file"))
+		goto cleanup;
+	btf = btf__new_empty();
+	if (!ASSERT_OK_PTR(btf, "btf_new_empty"))
+		goto cleanup;
+	btf__add_int(btf, "int", 4, BTF_INT_SIGNED);
+	if (!ASSERT_OK(btf__load_into_kernel(btf), "btf_load"))
+		goto cleanup;
+	fds[0] = -1;
+	fds[1] = btf__fd(btf);
+
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_type = BPF_PROG_TYPE_SYSCALL;
+	attr.insns = ptr_to_u64(insns);
+	attr.insn_cnt = ARRAY_SIZE(insns);
+	attr.license = ptr_to_u64("Dual BSD/GPL");
+	attr.prog_flags = BPF_F_SLEEPABLE;
+	attr.fd_array = ptr_to_u64(fds);
+	attr.fd_array_cnt = 0; /* sparse: force lazy kfunc BTF resolution */
+	attr.signature = ptr_to_u64(sig);
+	attr.signature_size = sig_sz;
+	attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
+	memcpy(attr.prog_name, "signed_kfunc", sizeof("signed_kfunc"));
+
+	prog_fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
+			  offsetofend(union bpf_attr, keyring_id));
+	err = prog_fd < 0 ? -errno : prog_fd;
+	if (prog_fd >= 0)
+		close(prog_fd);
+
+	ASSERT_EQ(err, -EACCES, "module kfunc BTF in signed program rejected");
+cleanup:
+	if (btf)
+		btf__free(btf);
+	run_setup("cleanup", dir);
+}
+
 void test_signed_loader(void)
 {
-	if (test__start_subtest("metadata_check_shape"))
-		metadata_check_shape();
+	if (test__start_subtest("loadtime_no_map"))
+		loadtime_no_map();
+	if (test__start_subtest("loadtime_with_map"))
+		loadtime_with_map();
 	if (test__start_subtest("metadata_match"))
 		metadata_match();
-	if (test__start_subtest("metadata_sha_mismatch"))
-		metadata_sha_mismatch();
-	if (test__start_subtest("metadata_not_exclusive"))
-		metadata_not_exclusive();
-	if (test__start_subtest("metadata_hash_not_computed"))
-		metadata_hash_not_computed();
 	if (test__start_subtest("signature_enforced"))
 		signature_enforced();
+	if (test__start_subtest("signed_nonexcl_fd_array_rejected"))
+		signed_nonexcl_fd_array_rejected();
+	if (test__start_subtest("signed_unfrozen_fd_array_rejected"))
+		signed_unfrozen_fd_array_rejected();
+	if (test__start_subtest("signed_nonarray_fd_array_rejected"))
+		signed_nonarray_fd_array_rejected();
+	if (test__start_subtest("signed_btf_fd_array_rejected"))
+		signed_btf_fd_array_rejected();
+	if (test__start_subtest("signed_module_kfunc_rejected"))
+		signed_module_kfunc_rejected();
+	if (test__start_subtest("signature_failure_logs"))
+		signature_failure_logs();
 	if (test__start_subtest("signature_too_large"))
 		signature_too_large();
 	if (test__start_subtest("signature_bad_keyring"))
@@ -1114,6 +1782,8 @@ void test_signed_loader(void)
 		metadata_ctx_initial_value_ignored();
 	if (test__start_subtest("signature_authenticates_insns"))
 		signature_authenticates_insns();
+	if (test__start_subtest("signature_authenticates_metadata"))
+		signature_authenticates_metadata();
 	if (test__start_subtest("hash_requires_frozen"))
 		hash_requires_frozen();
 	if (test__start_subtest("no_update_after_freeze"))
@@ -1132,4 +1802,10 @@ void test_signed_loader(void)
 		map_hash_unsupported_type();
 	if (test__start_subtest("lsm_signature_verdict"))
 		lsm_signature_verdict();
+	if (test__start_subtest("signed_no_fd_array"))
+		signed_no_fd_array();
+	if (test__start_subtest("signed_map_by_fd_rejected"))
+		signed_map_by_fd_rejected();
+	if (test__start_subtest("signed_sparse_fd_array_rejected"))
+		signed_sparse_fd_array_rejected();
 }
diff --git a/tools/testing/selftests/bpf/progs/test_signed_loader.c b/tools/testing/selftests/bpf/progs/test_signed_loader.c
index d9a4b85f9391..50451a69b99a 100644
--- a/tools/testing/selftests/bpf/progs/test_signed_loader.c
+++ b/tools/testing/selftests/bpf/progs/test_signed_loader.c
@@ -4,10 +4,11 @@
 
 /*
  * Minimal, map-less program. Driven through libbpf's gen_loader (gen_hash)
- * by prog_tests/signed_loader.c so the generated light-skeleton loader (with
- * the emit_signature_match metadata check) can be exercised against good
- * and tampered metadata. A socket filter needs no load-time attach resolution,
- * and having no maps keeps the generated loader's ctx trivial (0 maps, 1 prog).
+ * by prog_tests/signed_loader.c so the generated light-skeleton loader can be
+ * exercised against good and tampered metadata, which the kernel now verifies
+ * at load time via the insns||metadata signature. A socket filter needs no
+ * load-time attach resolution, and having no maps keeps the generated loader's
+ * ctx trivial (0 maps, 1 prog).
  */
 SEC("socket")
 int probe(void *ctx)
-- 
2.43.0

[PATCH bpf-next v4 9/9] Documentation/bpf: Add BPF signing and enforcement doc

[Daniel Borkmann]

Describe the BPF signing design end to end: why a trusted loader is
needed, the signature(insns || metadata) contract, load-time
verification via fd_array (exclusive + frozen maps), the binary
BPF_SIG_{UNSIGNED,VERIFIED} verdict, and how [BPF] LSMs can enforce
policy on it.

This writes down the contract on the discussion points with the LSM /
integrity folks [0][1]: by the time security_bpf_prog_load() is
called, signature verification has fully completed and covers the
instructions plus the frozen contents of every bound exclusive map;
there is no intermediate "loader verified, payload pending" state
to reason about; and what BPF_SIG_VERIFIED means at each hook is
spelled out explicitly.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/bc823ddbaf63e0e177eb46d1cc15076e4e2e689d.camel@HansenPartnership.com [0]
Link: https://lore.kernel.org/bpf/CAHC9VhSDkwGgPfrBUh7EgBKEJj_JjnY68c0YAmuuLT_i--GskQ@mail.gmail.com [1]
---
 Documentation/bpf/index.rst   |   1 +
 Documentation/bpf/signing.rst | 496 ++++++++++++++++++++++++++++++++++
 2 files changed, 497 insertions(+)
 create mode 100644 Documentation/bpf/signing.rst

diff --git a/Documentation/bpf/index.rst b/Documentation/bpf/index.rst
index 0d5c6f659266..638a00d42bc2 100644
--- a/Documentation/bpf/index.rst
+++ b/Documentation/bpf/index.rst
@@ -28,6 +28,7 @@ that goes into great technical depth about the BPF Architecture.
    classic_vs_extended.rst
    bpf_iterators
    bpf_licensing
+   signing
    test_debug
    clang-notes
    linux-notes
diff --git a/Documentation/bpf/signing.rst b/Documentation/bpf/signing.rst
new file mode 100644
index 000000000000..446b4edbae62
--- /dev/null
+++ b/Documentation/bpf/signing.rst
@@ -0,0 +1,496 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============
+BPF signing
+============
+
+This document describes how BPF programs are cryptographically signed, how the
+kernel verifies them at load time, and how Linux Security Modules (LSMs) -
+including the BPF LSM - use the resulting verdict to enforce policy. It is
+written for developers who want to produce signed BPF objects, understand what
+the signature actually guarantees, or build a policy on top of it.
+
+Motivation
+==========
+
+A signed BPF program lets the kernel establish that the bytecode being loaded
+originates from a trusted producer and was not modified in transit. On its own
+the kernel does not *require* signatures - an unsigned program loads exactly as
+before - but it records a verdict (see `The verdict`_) that an LSM can gate on.
+This is the building block for policies such as "only run BPF that was signed by
+a key in the trusted keyring", as could in the future be enforced by an LSM
+such as IPE.
+
+Signing is orthogonal to the existing permission model: it does not replace the
+capability checks or the verifier. A signed load still requires the usual
+privileges (``CAP_BPF`` and any program-type-specific capability, subject to
+``kernel.unprivileged_bpf_disabled``), and the loader's instructions are still
+checked by the verifier like any other program. A valid signature establishes
+*origin and integrity*, not safety - it lets a policy trust where the bytecode
+came from, it does not let a load skip any check it would otherwise face.
+
+The hard part is *what* gets signed. A naive scheme would sign a program's
+instruction buffer at build time and verify that signature at
+``BPF_PROG_LOAD``. That does not survive contact with real BPF objects, because
+the bytes the kernel finally loads are not the bytes the developer built and
+signed. Between the two, libbpf and the kernel rewrite the program:
+
+- **map file descriptors** are patched into ``ld_imm64`` instructions
+  (``BPF_PSEUDO_MAP_FD``), and a map's fd is assigned at load time, so it
+  differs on every run;
+- **CO-RE relocations** rewrite field offsets, sizes and existence flags against
+  the *running* kernel's BTF, so the result differs from one kernel to the next;
+- **kfunc and ksym references** are resolved to ids/addresses in the running
+  kernel;
+- **global data** (``.rodata``/``.data``/``.bss``) is created and seeded as maps
+  at load.
+
+So a signature over the original instructions cannot match the relocated
+instructions the verifier ends up checking, and the relocated form cannot be
+produced ahead of time because it depends on the target kernel. There is no
+fixed byte string that is both signable at build time and what the kernel
+actually loads - which is why a program cannot simply be signed and loaded
+directly.
+
+The trusted loader
+==================
+
+The solution is to move that setup work *into* a small BPF program - the
+**loader** - and sign the loader instead of the individual programs. libbpf's
+``gen_loader`` machinery (``bpftool gen skeleton -L``, the "light skeleton")
+emits a ``BPF_PROG_TYPE_SYSCALL`` program whose body performs the bpf() syscalls
+that create maps, apply relocations, and load the real programs. The payload it
+installs - the serialized programs, map descriptions, relocation data and
+initial values - lives in a separate array map, the **metadata map**
+(``__loader.map``).
+
+So the unit of trust is the loader, and the signing contract is::
+
+    Sig(I_loader || D_meta)
+
+where ``I_loader`` is the loader's instruction stream and ``D_meta`` is the
+content of the metadata map. Verifying the loader's signature establishes that
+both the loader *and* the payload it is about to install are authentic. The
+loader is reproducible: ``gen_loader`` builds it from primitives so the same
+object yields the same bytes on any build host.
+
+Why the loader is signable when the program is not
+--------------------------------------------------
+
+The loader sidesteps every rewrite listed above, because the bytes that are
+signed are *relocation-invariant*:
+
+- The loader's own instructions are a fixed sequence of bpf() syscalls emitted
+  by ``gen_loader``; they carry no CO-RE relocations and resolve no ksyms, so
+  they are identical on every kernel. The metadata map is referenced by *index*
+  into ``fd_array`` (``BPF_PSEUDO_MAP_IDX_VALUE``), not by a baked-in file
+  descriptor, so even that reference does not change between build and load.
+  The loader instruction bytes the kernel verifies are exactly the bytes that
+  were signed.
+- The metadata map is opaque, frozen data - the serialized target programs,
+  their relocation records, map descriptions and initial values. Its bytes are
+  identical at build time and at load time, so they are simply appended to the
+  instructions and covered by the same signature (there is no separate metadata
+  hash to compute or compare).
+
+All the host-specific rewriting - creating maps, patching their fds into the
+target programs, applying CO-RE, resolving ksyms, seeding global data - still
+happens, but it happens *inside the loader at runtime*, on the verified
+metadata, **after** the kernel has verified the ``insns || metadata`` signature.
+The kernel never has to verify the relocated target programs: it verifies the
+loader and its inputs once, and trust transfers to whatever that now-trusted,
+deterministic loader installs. The relocation step is moved from "before the
+signature can be checked" to "after a trusted program runs" - which is exactly
+what makes it signable.
+
+Because the metadata map is the loader's only untrusted input, two existing map
+properties are reused to keep it trustworthy across the load:
+
+Exclusive maps
+    A map created with ``excl_prog_hash`` (see ``BPF_MAP_CREATE``) may only be
+    accessed by a program whose digest matches that hash. The verifier enforces
+    ``map->excl_prog_sha == prog->digest`` for every map a program uses, so the
+    metadata map is bound to exactly the signed loader and cannot be shared with
+    or mutated by another program.
+
+Frozen maps
+    The metadata map is frozen (``BPF_MAP_FREEZE``) before the loader is loaded.
+    Freezing blocks further userspace writes, so the bytes folded into the
+    signature cannot change before the loader runs. (Freezing does not make the
+    map read-only to the loader program itself, which still writes created file
+    descriptors back into the blob's scratch area.)
+
+Load-time verification
+=======================
+
+Rather than have the loader check its own metadata from within BPF, the kernel
+verifies it directly at ``BPF_PROG_LOAD``, with no new UAPI. The mechanism
+reuses the existing ``fd_array``:
+
+#. Userspace creates the metadata map with ``excl_prog_hash`` set to the
+   loader's digest, populates it, and freezes it.
+#. The loader is loaded with ``signature``/``signature_size``/``keyring_id``
+   set, the metadata map referenced through ``fd_array``, and ``fd_array_cnt``
+   set so the kernel knows the array's length.
+#. Signature verification runs inside the verifier (``bpf_check()``), once it
+   has resolved the ``fd_array`` entries into the program's ``used_maps``. The
+   maps folded into the signature are therefore the very objects the program
+   binds - a single resolution of ``fd_array``, not a separate read, so the
+   verified bytes cannot be swapped for a different map after the check (no
+   time-of-check/time-of-use window). Each folded map must be exclusive (carry
+   ``excl_prog_sha``) and a plain array map (``BPF_MAP_TYPE_ARRAY``); only an
+   array map exposes its value buffer through ``map_direct_value_addr()`` as a
+   kernel address spanning ``value_size`` bytes. A map that is not exclusive, not
+   frozen, or not a plain array is rejected, with a verifier log message naming
+   the offending map. The kernel appends each map's frozen
+   contents to the instruction buffer and verifies the PKCS#7 signature over the
+   concatenation ``insns || metadata_0 || metadata_1 || ...`` in ``used_maps``
+   order, before it rewrites the (signed) instructions.
+
+A signed program therefore takes one of exactly two shapes, both fully
+supported:
+
+- **No bound maps** (``fd_array_cnt == 0``): there is nothing to append, so the
+  kernel verifies the signature over the instructions alone. A valid signature
+  yields ``BPF_SIG_VERIFIED`` and the program loads. This is the ordinary case
+  for a directly-loaded signed program with no separate payload; it is *not*
+  rejected for "missing" metadata, because it has none to cover.
+- **Exclusive bound maps** (``fd_array_cnt > 0``): every entry is exclusive and
+  folded, so the signature covers ``insns || metadata``.
+
+There is no third shape: a non-exclusive map in a signed program's ``fd_array``
+is rejected rather than silently left out of the signature, so a program bound
+to a signed loader never has a map the signature does not cover.
+
+The digest binding (``excl_prog_sha == prog->digest``) is enforced by the
+verifier as usual; because that check runs while ``fd_array`` is resolved -
+before the verifier would otherwise compute the tag - ``prog->digest`` is
+computed up front in the verifier, over the unmodified (signature-covered)
+instructions, for any signed load.
+
+Coverage is then enforced as the verifier resolves instructions, at the point
+each object is bound rather than by a count taken afterwards. Once the signature
+has been verified, binding any further map is refused: a map reached by a
+directly-referenced fd, or a map swapped into an ``fd_array`` slot the loader
+reads, is not among those already folded, so it is rejected the moment the
+verifier tries to bind it. A BTF is refused outright for a signed program - a
+ksym or a BTF fd in ``fd_array``, whether resolved up front or lazily for a
+module kfunc, is rejected when it would be bound. Together with the fold rule
+above this keeps the verdict binary: a signed program cannot use a map its
+signature does not cover, and a different but equally digest-bound map cannot be
+substituted at an ``fd_array`` slot. Non-exclusive maps are never folded, so a
+signed program cannot use one at all.
+
+The verdict
+===========
+
+A program is either unsigned or fully verified - there is no intermediate
+state. The outcome is recorded in ``prog->aux->sig.verdict``:
+
+.. code-block:: c
+
+    enum bpf_sig_verdict {
+            BPF_SIG_UNSIGNED = 0,
+            BPF_SIG_VERIFIED,
+    };
+
+``BPF_SIG_VERIFIED`` means the signature is valid and covers the instructions
+*and* the frozen contents of every exclusive map the program uses:
+
+- For an ordinary, directly-loaded signed program the instructions are the whole
+  artifact and it uses no exclusive maps, so a valid instruction signature is
+  the complete verification.
+- For a signed loader the metadata map is exclusive, so its contents are folded
+  in and the signature covers ``insns || metadata``.
+
+There is deliberately no "instructions verified but metadata not" verdict: a
+signed loader that fails to cover its metadata is *rejected* (see above), not
+recorded with a weaker verdict. ``BPF_SIG_VERIFIED`` therefore always means the
+program and everything the signature is responsible for are authentic, which is
+what a policy can rely on.
+
+Alongside the verdict the kernel records which keyring validated the signature;
+see `Keyrings`_.
+
+Enforcement via LSMs
+====================
+
+Signing only *records* a verdict; an LSM turns it into policy. The verdict and
+keyring fields live in ``struct bpf_prog_aux``, so a BPF LSM program can read
+them directly (see Documentation/bpf/prog_lsm.rst for writing and attaching BPF
+LSM programs); the same fields are equally available to in-tree LSMs. Two hooks
+are useful at different points of the load: the dedicated
+``security_bpf_prog_load()`` gates admission before the main verification work,
+and the existing ``security_bpf_prog()`` observes a program that has fully
+loaded.
+
+Admission: ``security_bpf_prog_load()``
+---------------------------------------
+
+This hook gates admission **for every load**, from a single call site inside the
+verifier (``bpf_check()``), before the main verification work. It runs after the
+optional signature verification, so the verdict and keyring fields are final - the
+hook can see whether, and how strongly, the program was signed, which keyring
+validated it, the load ``attr``, the BPF token and whether the load came from the
+kernel. For a signed load the verdict is ``BPF_SIG_VERIFIED`` here (the signature
+has just been checked); for an unsigned load it is ``BPF_SIG_UNSIGNED``.
+
+This is the place for *coarse admission* that must also see unsigned and
+not-yet-verified loads: require a signature at all, restrict the acceptable
+keyring, restrict which token/credentials may load BPF, apply per-program-type
+rules, or audit every load attempt that makes it past signature verification -
+attempts failing the signature or the metadata binding abort before this hook
+fires. It is the primary deny point.
+
+One subtlety: this hook runs *before* the verifier finishes its work, so
+``BPF_SIG_VERIFIED`` *here* means only "validly signed" - not "loaded". Allowing
+a load at this point lets it *proceed*; it does not guarantee the program will
+load. A validly signed program can still be rejected afterwards on two
+independent grounds: the verifier may reject it like any other program (unsafe
+memory access, bad control flow, resource limits, ...), and the kernel separately
+refuses - as the verifier resolves instructions and binds each object - any map
+the signature does not cover or any BTF at all, regardless of what this hook
+returned. Only after the program has fully loaded, at the next hook
+(``security_bpf_prog()``), does ``BPF_SIG_VERIFIED`` carry its full meaning:
+validly signed *and* fully verified.
+
+A more realistic admission policy than "is it signed at all": accept programs
+signed by a system keyring, accept a user-keyring signature only if the
+key/keyring it was verified against is on an explicit allowlist, and emit a
+tamper-evident record of every decision so that even denied attempts are
+auditable. (Illustrative - error checking elided.)
+
+.. code-block:: c
+
+    /* Serials of user keys/keyrings we additionally trust. */
+    struct {
+            __uint(type, BPF_MAP_TYPE_HASH);
+            __type(key, __s32);             /* keyring_serial */
+            __type(value, __u8);
+            __uint(max_entries, 64);
+    } trusted_user_keys SEC(".maps");
+
+    /* Audit stream consumed by a userspace logger. */
+    struct {
+            __uint(type, BPF_MAP_TYPE_RINGBUF);
+            __uint(max_entries, 1 << 16);
+    } audit SEC(".maps");
+
+    struct decision { __u32 prog_type, verdict, ktype; __s32 serial, ret; };
+
+    SEC("lsm/bpf_prog_load")
+    int BPF_PROG(admit, struct bpf_prog *prog, union bpf_attr *attr,
+                 struct bpf_token *token, bool kernel)
+    {
+            __u32 verdict = prog->aux->sig.verdict;
+            __u32 ktype   = prog->aux->sig.keyring_type;
+            __s32 serial  = prog->aux->sig.keyring_serial;
+            struct decision *d;
+            int ret = 0;
+
+            if (kernel)
+                    return 0;                       /* trust in-kernel loads */
+
+            if (verdict != BPF_SIG_VERIFIED)
+                    ret = -EPERM;                   /* must be validly signed */
+            else if (ktype == BPF_SIG_KEYRING_USER &&
+                     !bpf_map_lookup_elem(&trusted_user_keys, &serial))
+                    ret = -EPERM;                   /* key/keyring not allowlisted */
+
+            d = bpf_ringbuf_reserve(&audit, sizeof(*d), 0);
+            if (d) {
+                    d->prog_type = attr->prog_type;
+                    d->verdict = verdict;
+                    d->ktype = ktype;
+                    d->serial = serial;
+                    d->ret = ret;
+                    bpf_ringbuf_submit(d, 0);       /* record allow *and* deny */
+            }
+            return ret;
+    }
+
+Observing a verified load: ``security_bpf_prog()``
+--------------------------------------------------
+
+There is deliberately no separate "metadata attested" hook. The coverage check
+above is enforced by the kernel unconditionally, so a signed loader that fails
+to cover its metadata never loads and an LSM never has to re-establish that
+fact. To *act on* a program that has successfully and fully loaded, use the
+existing ``security_bpf_prog()`` hook (``lsm/bpf_prog``), which fires from
+``bpf_prog_new_fd()`` - after the verifier, after the coverage check, and after
+``bpf_prog_alloc_id()``. Relative to the admission hook this point is strictly
+later and stronger:
+
+- the program has an id (``prog->aux->id``), so it can be recorded or correlated
+  with later events;
+- ``verdict == BPF_SIG_VERIFIED`` *here* means **fully** verified - a program
+  that used a map the signature does not cover was already rejected, so it cannot
+  reach this point;
+- it observes only programs that actually loaded; a failed load never mints an
+  fd, so it never reaches this hook.
+
+It takes only the ``prog`` and a non-zero return still aborts (the fd is not
+handed out), so it can veto as well as observe. One wrinkle: it also fires on
+other paths that mint a new program fd - notably ``bpf_prog_get_fd_by_id()`` -
+not just on a fresh load. Because the program already has its id here, an LSM
+can tell the two apart with a small hash map: the *first* time an id is seen is
+the load; a later sighting of the same id is just another fd to a program that
+already exists.
+
+To bound the map and let a reused id read as a fresh load, this can be paired
+with ``security_bpf_prog_free()`` (``lsm/bpf_prog_free``), which deletes the
+entry on teardown - keyed by the same ``prog`` pointer, since
+``bpf_prog_free_id()`` has already cleared ``prog->aux->id`` to ``0`` by the time
+that hook runs. (Illustrative - privileged LSM, error checking elided.)
+
+.. code-block:: c
+
+    struct rec { __u32 id, ktype; __s32 serial; };
+
+    struct {
+            __uint(type, BPF_MAP_TYPE_HASH);
+            __type(key, __u64);             /* struct bpf_prog * -- stable id */
+            __type(value, struct rec);
+            __uint(max_entries, 4096);
+    } live SEC(".maps");
+
+    SEC("lsm/bpf_prog")            /* fires after load and on every later fd */
+    int BPF_PROG(observe, struct bpf_prog *prog)
+    {
+            __u64 key = (__u64)(unsigned long)prog;
+            struct rec r;
+
+            if (prog->aux->sig.verdict != BPF_SIG_VERIFIED)
+                    return 0;
+            if (bpf_map_lookup_elem(&live, &key))
+                    return 0;               /* seen before: a later fd, not a load */
+
+            /* First sighting == this program just loaded; id is valid here. */
+            r.id     = prog->aux->id;
+            r.ktype  = prog->aux->sig.keyring_type;
+            r.serial = prog->aux->sig.keyring_serial;
+            bpf_map_update_elem(&live, &key, &r, BPF_NOEXIST);
+            /* ... newly-loaded verified-program action, e.g. record r.id ... */
+            return 0;
+    }
+
+Putting them together: to *require* verified BPF, deny at the admission hook
+unless the verdict is ``BPF_SIG_VERIFIED`` (and, if desired, restrict the
+keyring). The kernel then guarantees that any program which actually loads with
+that verdict covered all of its exclusive maps, rejecting any that did not - so
+a deny-by-default admission policy needs no second enforcement point. Use
+``security_bpf_prog()`` to record or finally gate the verified programs once
+they carry an id. The ``verdict``, ``keyring_type`` and ``keyring_serial`` fields
+let a policy distinguish, for example, "verified and signed by a builtin key"
+from "verified by a user key". A policy LSM such as IPE could consume the same
+hooks to enforce system policy without writing any BPF, though none implements
+this today.
+
+Keyrings
+========
+
+``keyring_id`` selects the trusted keyring the PKCS#7 signature is verified
+against. The well-known ids ``0`` (builtin), ``VERIFY_USE_SECONDARY_KEYRING``
+and ``VERIFY_USE_PLATFORM_KEYRING`` select the corresponding system keyrings;
+any other value is treated as the serial of a user/session key or keyring.
+The keyring is looked up first, before the signature bytes are examined, so a
+signature naming a non-existent keyring is rejected up front, and a failed
+verification aborts the load - so a program that loads successfully with a
+signature always has consistent keyring fields recorded.
+
+Two fields are recorded in ``prog->aux->sig`` for an LSM to inspect:
+
+``keyring_type`` (``enum bpf_sig_keyring``)
+    Classified purely from ``keyring_id`` whenever the program is signed:
+    ``BPF_SIG_KEYRING_BUILTIN``, ``_SECONDARY``, ``_PLATFORM`` for the system
+    keyrings, or ``_USER`` for a user/session keyring. It is
+    ``BPF_SIG_KEYRING_NONE`` for an unsigned program.
+
+``keyring_serial`` (``s32``)
+    Set **only** on a successful verification, to the serial of the
+    **user/session key or keyring** that ``keyring_id`` resolved to - the
+    object the signature was verified against, not the individual asymmetric
+    key inside it that matched the signer. Passing
+    ``KEY_SPEC_SESSION_KEYRING``, for example, records the session keyring's
+    serial. The system keyrings are trusted as a whole and expose no serial
+    here, so the serial is ``0`` for builtin, secondary and platform
+    signatures, and ``0`` for unsigned programs. In other words, a non-zero
+    ``keyring_serial`` is exactly "verified against the user key/keyring with
+    this serial".
+
+.. list-table::
+   :header-rows: 1
+
+   * - ``keyring_id``
+     - ``keyring_type``
+     - ``keyring_serial``
+   * - (no signature)
+     - ``BPF_SIG_KEYRING_NONE``
+     - ``0``
+   * - ``0``
+     - ``BPF_SIG_KEYRING_BUILTIN``
+     - ``0``
+   * - ``VERIFY_USE_SECONDARY_KEYRING``
+     - ``BPF_SIG_KEYRING_SECONDARY``
+     - ``0``
+   * - ``VERIFY_USE_PLATFORM_KEYRING``
+     - ``BPF_SIG_KEYRING_PLATFORM``
+     - ``0``
+   * - other (a user/session key serial)
+     - ``BPF_SIG_KEYRING_USER``
+     - serial of the resolved key/keyring
+
+Producing a signed object
+==========================
+
+``bpftool`` generates and signs a light skeleton in one step::
+
+    bpftool gen skeleton -L -S -k <private_key.pem> -i <certificate.x509> \
+            obj.bpf.o > obj.lskel.h
+
+``-L`` selects the light-skeleton (``gen_loader``) backend and ``-S`` enables
+signing; ``-k`` and ``-i`` supply the signing key and its X.509 certificate.
+``bpftool`` signs ``insns || metadata`` - the exact bytes the kernel
+reconstructs - and also computes ``excl_prog_hash`` as the digest of the loader
+instructions so the metadata map can be bound to the loader. The signature and
+hash are embedded in the generated header; the certificate is used only for
+signing and is not included. Loading the skeleton performs the
+create/populate/freeze/load sequence described above.
+
+At runtime the trusted public key must be present in the chosen keyring (for
+example added to the session keyring, or built into the kernel's builtin trusted
+keyring) for verification to succeed.
+
+UAPI reference
+==============
+
+``BPF_PROG_LOAD`` (``union bpf_attr``):
+
+``signature``, ``signature_size``
+    Pointer to and length of the PKCS#7 signature blob.
+
+``keyring_id``
+    Trusted keyring selector (see `Keyrings`_).
+
+``fd_array``, ``fd_array_cnt``
+    Array of map file descriptors bound to the program. ``fd_array_cnt`` must be
+    set for the kernel to scan the array. When a signature is present, every map
+    in the array must be exclusive; its frozen contents are folded into the
+    verified buffer, and a non-exclusive entry is rejected.
+
+``BPF_MAP_CREATE`` (``union bpf_attr``):
+
+``excl_prog_hash``, ``excl_prog_hash_size``
+    SHA-256 digest of the program permitted to access this (exclusive) map. This
+    binds the metadata map to the loader; it is not a hash of the map *content*.
+    The map content is not hashed separately at all - it is covered, as bytes,
+    by the program signature.
+
+Notes and limitations
+======================
+
+- The instructions plus folded metadata are verified as one ``bpf_dynptr``,
+  which bounds the combined size (currently ~16 MiB); very large objects can
+  exceed it.
+- The metadata container is a single-element array map, accessed through
+  ``map_direct_value_addr``.
-- 
2.43.0

Re: [PATCH bpf-next v4 4/9] libbpf: Drop in-loader metadata check for load-time verification

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 2897 bytes --]

> commit eb80a2d94081929e7d91f275cdeda214433dead7
> Author: Daniel Borkmann <daniel@iogearbox.net>
> Date:   Mon Jul 6 15:56:39 2026 +0200
>
>     libbpf: Drop in-loader metadata check for load-time verification
>
>     The signed gen_loader used to police its own metadata map from within
>     BPF: emit_signature_match() read the kernel-cached map->sha[] back
>     through hardcoded struct bpf_map offsets and compared it against a hash
>     that compute_sha_update_offsets() baked into the signed instructions,
>     after a BPF_OBJ_GET_INFO_BY_FD round-trip to populate map->sha[].
>
>     The kernel now verifies the metadata at BPF_PROG_LOAD time by folding
>     the frozen contents of the loader's exclusive fd_array maps into the
>     signature, so the loader no longer checks anything itself. Generated
>     loaders thus carry no verification logic of their own anymore: Nothing
>     in the signing chain depends on emitted loader bytecode doing the right
>     thing.
>
>     On the loading side, skel_internal.h now sets fd_array_cnt for a signed
>     load so the kernel scans fd_array for the exclusive metadata map -
>     still frozen, as the kernel requires - and the BPF_OBJ_GET_INFO_BY_FD
>     round-trip to populate map->sha[] is gone. The struct bpf_map layout
>     BUILD_BUG_ON()s on the kernel side are removed as well: they only
>     pinned the ABI for the in-BPF read of map->sha[] that is no longer
>     needed. Same for the map->excl member. Note: gen_hash is retained; it
>     still marks a loader as signed so an untrusted host cannot re-dimension
>     maps or override initial values now covered by the signature.
>
>     Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

In reviewing the patch series discussion on lore, Paul Moore raised a
security concern in v3 about the companion patch that moves the
security_bpf_prog_load() LSM hook into bpf_check() in verifier.c. He
noted that the moved hook placement allows processes to allocate kernel
memory (including bpf_verifier_env via kvzalloc_obj) before SELinux can
deny the BPF program load operation, creating a potential local DoS
attack vector where even denied operations trigger sizable allocations.

Paul explicitly Nacked the change with:

    Nacked-by: Paul Moore (don't move bpf_prog_load LSM hook)
    <paul@paul-moore.com>

Reference:
https://lore.kernel.org/bpf/CAHC9VhQD4RHsGiTMVCCTN+eB71-Ueopke8XghExpNJ2PSNa_jQ@mail.gmail.com/

Paul did not comment on v4, leaving it unclear whether his concern was
addressed or if he accepted the change. Has this security regression
concern been resolved, or does the hook movement remain in the series?


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/28797884155

Re: [PATCH bpf-next v4 3/9] bpf: Verify signed loader metadata at load time

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 3502 bytes --]

> A signed gen_loader program carries the programs, maps and relocations
> it installs in a metadata array map. The loader instructions are covered
> by the PKCS#7 signature, but the metadata map is not: Today the loader
> compares the map contents from within BPF against a hash baked into its
> (signed) instructions, using the kernel-cached map hash. The kernel
> itself never actually attests that the metadata the loader installs is
> the metadata that was signed.
>
> [ ... ]
>
> A signed loader binds its metadata map(s) through the existing fd_array,
> and an exclusive map is already bound to a program digest (excl_prog_hash).
> So when a signature is present, collect the exclusive maps from fd_array
> and append their frozen contents to the instructions before verification:
> The signature now covers insns || metadata_0 || metadata_1 || [...] in
> the fd_array order, and verification completes in bpf_check(), once the
> fd_array maps are resolved into used_maps, before the LSM admission hook
> and the rest of verification.
>
> [ ... ]
>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

This changes how the existing BPF program signing scheme attests the
loader payload, and reworks the verification that was added when
signature support first landed.

Should it carry a Fixes: tag pointing at the commit that introduced the
signing scheme, for example:

  Fixes: 349271568303 ("bpf: Implement signature verification for BPF programs")

That commit added attr->signature/signature_size/keyring_id and the
original bpf_prog_verify_signature() that only covered prog->insnsi. The
later commit ea1535e28bb3 ("bpf: Limit bpf program signature size")
already uses this same target.

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index e227c76a8dd9..65f53128fc33 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c

[ ... ]

> @@ -19909,11 +20068,27 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
>  	ret = bpf_vlog_init(&env->log, attr_log->level, attr_log->ubuf, attr_log->size);
>  	if (ret)
>  		goto err_free_env;
> +	if (env->signature) {
> +		ret = bpf_prog_calc_tag(env->prog);
> +		if (ret < 0)
> +			goto err_prep;
> +	}
>
>  	ret = process_fd_array(env, attr, uattr);
>  	if (ret)
>  		goto err_prep;
>
> +	if (env->signature) {
> +		ret = bpf_prog_verify_signature(env, attr, uattr.is_kernel);
> +		if (ret)
> +			goto err_prep;
> +	}
> +
> +	ret = security_bpf_prog_load(env->prog, attr, env->prog->aux->token,
> +				     uattr.is_kernel);
> +	if (ret)
> +		goto err_prep;

This moves the security_bpf_prog_load() admission hook out of
bpf_prog_load() in syscall.c and into bpf_check(), now placed after
process_fd_array().

At this point the program instructions have already been allocated and
copied in, up to the maximum program size. Does relocating the hook here
mean that for a policy which denies a load, the denial now happens only
after that allocation, rather than before it as in the previous
placement?

This placement carries a Nacked-by from the LSM maintainer on the same
grounds, and the code keeps the hook in the new location. Is it worth
resolving that objection before this lands, or is the intent to leave it
for the merge-window decision?


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/28797884155

Re: [PATCH bpf-next v4 1/9] bpf: Resolve and cache fd_array objects at load time

[Anton Protopopov]

On 26/07/06 03:56PM, Daniel Borkmann wrote:
> The fd_array passed to BPF_PROG_LOAD carries the map and module BTF file
> descriptors a program binds. The verifier reads it more than once during
> a load: process_fd_array() walks it to bind the maps and BTFs, and
> check_and_resolve_insns() and the kfunc BTF resolver later read it again
> to resolve the program's BPF_PSEUDO_MAP_IDX* and module kfunc refs.
> 
> For signed BPF, we need these upfront in memory, thus resolve each fd to
> its object once and cache it by fd_array index, then bind that cached
> object for the rest of the load. env->fd_array becomes a small per-slot
> {map, btf} cache rather than a bpfptr_t; every later reference is then
> an in-bounds lookup of an already-resolved object, and an index outside
> the cache is rejected instead of read from user memory:
> 
>   - continuous (fd_array_cnt given): the caller declares the length and
>     every entry is resolved and bound up front (used also by the BPF
>     signed loader)
> 
>   - sparse (no fd_array_cnt): left as the legacy path with no fd_array
>     cache; each reference reads its fd from the caller's fd_array and
>     resolves it on the spot. Deduplication in used_maps and the kfunc BTF
>     table keeps this correct, and only unsigned programs use this shape.
> 
> Split these into separate helpers to make it easier to follow.
> 
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Anton Protopopov <a.s.protopopov@gmail.com>
> ---
>  include/linux/bpf_verifier.h |  22 +++-
>  kernel/bpf/verifier.c        | 223 +++++++++++++++++++++++++++--------
>  2 files changed, 193 insertions(+), 52 deletions(-)

Acked-by: Anton Protopopov <a.s.protopopov@gmail.com>

> [...]
> -- 
> 2.43.0
> 

Re: [PATCH bpf-next v4 0/9] Verify BPF signed loader at load time

[Paul Moore]

On Mon, Jul 6, 2026 at 9:56 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> The BPF signing scheme signs a light skeleton's loader program and lets
> the loader vouch for everything else: bpftool bakes the SHA256 of the
> metadata map into the loader's instructions, signs the instructions, and
> the loader compares the (frozen, exclusive) map against that hash from
> within BPF once it runs. The construction is sound as a trusted hash
> chain, but the kernel itself never attests the metadata, and that split
> has been the recurring objection from the LSM / integrity side since the
> scheme was proposed.
>
> This proposal closes both gaps by having the kernel verify the metadata
> at BPF_PROG_LOAD time, before the LSM admission hook and before the
> verifier, /without/ growing the UAPI. A signed loader binds its metadata
> map(s) through the existing fd_array/fd_array_cnt, and exclusive maps
> are already bound to the loader's digest via excl_prog_hash. When a
> signature is present, the kernel collects the exclusive maps from the
> fd_array and appends their frozen contents to the instructions before
> PKCS#7 verification, so the signature covers ...
>
>     insns || metadata_0 || metadata_1 || [...]
>
> ... in fd_array order. The in-loader hash check is dropped from the
> gen_loader entirely: generated loaders carry no verification logic
> anymore, and signing or verifying a skeleton becomes an ordinary CMS
> operation over bytes that sit verbatim in the skeleton, reproducible
> offline. A signed program is either BPF_SIG_UNSIGNED or BPF_SIG_VERIFIED
> with nothing in between.
>
> There is no new UAPI, we now have a single signature scheme, no LSM
> code reaching into BPF internals, no new LSM hook, and unsigned loads
> are completely unaffected. It is also less complex since the loader
> does not need to deal with BTF, an extra kfunc, etc, as proposed in
> an earlier series [0]. Tested against full BPF CI which came back
> green. For more details and examples, see the documentation patch in
> this series.
>
>   [0] https://lore.kernel.org/bpf/20260522023234.3778588-1-kpsingh@kernel.org/
>
> v3 -> v4:
>   - Fix upper limit in MAX_FD_ARRAY_CNT (Anton)
>   - Reject !fd_array && attr->fd_array_cnt (Anton)
>   - Add bpftool patch wrt ignored return value of EVP_Digest() (sashiko)
>   - Fix setting of gen_loader_fixture_init (sashiko)
>   - Fix unused map_fd cleanup branch in selftest (bot+bpf-ci)
>   - Remove now unused map->excl member and adjust selftests
>   - Added more BPF signed_loader corner case selftest coverage
>   - Added Paul's Nack wrt bpf_prog_load LSM hook dispute
>   - Added patch 2 to move bigger allocations below fd_array
>     resolution (Paul)

If you want to squash patch 2/9 and 3/9 together so that one can't
easily merge 3/9 without the vzalloc(program) relocation I'll gladly
drop my NACK on patch 3/9.

> v2 -> v3:
>   - Added first commit to cache and work on objects in fd_array
>     which was the most recent issue sashiko rightfully complained
>   - Added more BPF signed_loader selftest coverage to cover that
>     usage of sparse fd_array or map fds gets rejected
>   - I left the security_bpf_prog_load as in v2 given preference
>     from BPF side over adding new hook
> v1 -> v2:
>   - Addressed both sashiko complaints, the TOCTOU bug regarding
>     fd_array processing, as well as exclusive map checking to
>     only allow array maps. The validation is now moved into the
>     verifier before the main verification work happens. This also
>     gives the opportunity to utilize the verifier log.
>
> Daniel Borkmann (9):
>   bpf: Resolve and cache fd_array objects at load time
>   bpf: Move bigger allocations below fd_array resolution
>   bpf: Verify signed loader metadata at load time
>   libbpf: Drop in-loader metadata check for load-time verification
>   bpftool: Check EVP_Digest when computing excl_prog_hash
>   bpftool: Cover loader metadata with the program signature
>   selftests/bpf: Adjust bpf_map layout in verifier_map_ptr
>   selftests/bpf: Verify load-time signed loader metadata
>   Documentation/bpf: Add BPF signing and enforcement doc
>
>  Documentation/bpf/index.rst                   |    1 +
>  Documentation/bpf/signing.rst                 |  496 ++++++++
>  include/linux/bpf.h                           |    1 -
>  include/linux/bpf_verifier.h                  |   23 +-
>  kernel/bpf/syscall.c                          |   83 +-
>  kernel/bpf/verifier.c                         |  450 ++++++--
>  tools/bpf/bpftool/gen.c                       |    2 +
>  tools/bpf/bpftool/sign.c                      |   24 +-
>  tools/lib/bpf/bpf_gen_internal.h              |    1 -
>  tools/lib/bpf/gen_loader.c                    |   76 +-
>  tools/lib/bpf/libbpf_internal.h               |    1 -
>  tools/lib/bpf/skel_internal.h                 |   31 +-
>  .../selftests/bpf/prog_tests/signed_loader.c  | 1004 ++++++++++++++---
>  .../selftests/bpf/progs/test_signed_loader.c  |    9 +-
>  .../selftests/bpf/progs/verifier_map_ptr.c    |   23 +-
>  15 files changed, 1786 insertions(+), 439 deletions(-)
>  create mode 100644 Documentation/bpf/signing.rst

-- 
paul-moore.com

Re: [PATCH bpf-next v4 3/9] bpf: Verify signed loader metadata at load time

[Paul Moore]

On Mon, Jul 6, 2026 at 9:56 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> A signed gen_loader program carries the programs, maps and relocations
> it installs in a metadata array map. The loader instructions are covered
> by the PKCS#7 signature, but the metadata map is not: Today the loader
> compares the map contents from within BPF against a hash baked into its
> (signed) instructions, using the kernel-cached map hash. The kernel
> itself never actually attests that the metadata the loader installs is
> the metadata that was signed.
>
> This split is the core of the long-standing objection to the BPF signing
> scheme from the LSM / integrity side: the integrity check of a light
> skeleton only completes once the loader program runs, that is, after the
> security_bpf_prog_load() hook, so at admission time an LSM observes a
> program whose payload has not yet been verified. Auditing the chain
> link is also not a purely cryptographic operation: whoever signs or
> reviews an lskel has to disassemble the loader's preamble to convince
> themselves that the embedded hash check is present and correct [0][1].
> Two acceptable fixes were identified in those threads: Complete the
> integrity check before the admission hook fires, or add a second hook
> that collects the verification result after the loader ran [2]. Covering
> both the loader and its maps directly with the PKCS#7 signature is what
> Blaise Boscaccy's patchsets proposed in several forms. Let's implement
> the former, without growing the UAPI, and in particular as a single
> unified scheme where the signature spans the raw bytes rather than
> derived hashes.
>
> A signed loader binds its metadata map(s) through the existing fd_array,
> and an exclusive map is already bound to a program digest (excl_prog_hash).
> So when a signature is present, collect the exclusive maps from fd_array
> and append their frozen contents to the instructions before verification:
> The signature now covers insns || metadata_0 || metadata_1 || [...] in
> the fd_array order, and verification completes in bpf_check(), once the
> fd_array maps are resolved into used_maps, before the LSM admission hook
> and the rest of verification. A program is either BPF_SIG_UNSIGNED or
> BPF_SIG_VERIFIED, with nothing in between. While folding the fd_array
> maps, a non-exclusive map bound to a signed program is rejected, so every
> map folded into the signature is exclusive. A signed loader that fails
> to cover its metadata thus does not load, and BPF_SIG_VERIFIED always
> means the instructions and every exclusive map are authentic. The maps
> must be frozen so the hashed bytes cannot change before the loader runs;
> the map <-> program digest binding is enforced by the verifier for every
> used map. Binding maps through fd_array_cnt makes the verifier resolve
> and excl-check them (excl_prog_sha vs prog->digest) before it would
> otherwise compute the digest, so compute prog->digest up front in
> bpf_check(), over the unmodified instructions the signature covers, for
> a load that folds metadata.
>
> Unsigned programs are not affected by the signature path; for them the
> LSM admission hook merely moves below fd_array resolution, with minimal
> bounded work in between (see the previous commit). Note, signed loaders
> generated by older libbpf/bpftool versions need to be regenerated; some
> of the recent fixes we've had on the signed loader side require the
> latter already to close gaps.
>
> Finally, some remarks around the security_bpf_prog_load() placement
> given there was pushback, demanding either a new hook or a reuse of
> the existing security_bpf_prog() hook [3]: Just for loading a single
> BPF program it would then need to pass through four layers of LSM hooks:
>
>   1) security_bpf (cmd=PROG_LOAD): for gating various bpf subcmds
>   2) security_bpf_prog_load: historical admission hook (CAP/token,
>      prog_type, attach point), pre-verification
>   3) security_bpf_prog_verify_signature: newly asked admission hook,
>      same role as 2), plus the BPF signature verdict
>   4) security_bpf_prog: gate handing the prog fd back to userspace,
>      verification done & signature verified
>
> The use-cases of 2) and 3) conflate, thus BPF community prefers to just
> keep a total of 3 LSM hooks (as-is today): 3) makes 2) incoherent given
> they are the /same class/ of hook, that is, access-control admission on
> the load and split only by _what_ they can see. Worse, with the split,
> for a signed BPF program security_bpf_prog_load 2) admits a program whose
> signature has not been checked, so a policy gating at 2) is structurally
> unable to express "admit only verified" and every such policy is forced
> onto 3) *anyway*. In other words, one doesn't get two complementary hooks,
> but rather, one real admission hook aka 3) plus a now-degraded /legacy/
> hook 2) that can't answer the question operators actually want to ask.
>
> Reusing security_bpf_prog() 4) for admission is no alternative either:
> it fires only after the entire verifier (and JIT) pipeline ran, so
> denying a not-yet-verified program at that point burns exactly the
> work a denial is supposed to avoid, and by then the program has an id
> assigned and the kallsyms/perf/audit load events fired. Policies are
> free to also consume the signature verdict at 4), but admission control
> belongs into security_bpf_prog_load(). Hence the latter remains the only
> admission hook, merely moved past signature verification; with moving
> large allocations further down into the BPF verifier, there is now only
> minimal work between the old and new location.

See my comment on patch 0/9, but if we can combine this patch with the
vzalloc(progam) patch, I'll be happy to drop my NACK, and you can trim
the last half of this patch description ;)

I suspect that squashing the two patches should also quiet sashiko's
comments as it will be able to see the vzalloc() below the
security_bpf_prog_load() hook in this same patch.

> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Nacked-by: Paul Moore <paul@paul-moore.com> # (don't move bpf_prog_load LSM hook)
> Link: https://lore.kernel.org/bpf/2f71d6c03698eb17d51f7247efde777627ee578a.camel@HansenPartnership.com [0]
> Link: https://lore.kernel.org/lkml/ecf0521ed302db672672ebfbc670ecfba36a6e00.camel@HansenPartnership.com [1]
> Link: https://lore.kernel.org/bpf/88703f00d5b7a779728451008626efa45e42db3d.camel@HansenPartnership.com [2]
> Link: https://lore.kernel.org/bpf/DJOFY21DYUI4.19WKQ3NPZ4H5R@gmail.com [3]
> ---
>  include/linux/bpf_verifier.h |   1 +
>  kernel/bpf/syscall.c         |  76 +--------------
>  kernel/bpf/verifier.c        | 175 +++++++++++++++++++++++++++++++++++
>  3 files changed, 178 insertions(+), 74 deletions(-)

-- 
paul-moore.com

Re: [PATCH bpf-next v4 0/9] Verify BPF signed loader at load time

[Daniel Borkmann]

Hi Paul,

On 7/6/26 7:13 PM, Paul Moore wrote:
> On Mon, Jul 6, 2026 at 9:56 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>>
>> The BPF signing scheme signs a light skeleton's loader program and lets
>> the loader vouch for everything else: bpftool bakes the SHA256 of the
>> metadata map into the loader's instructions, signs the instructions, and
>> the loader compares the (frozen, exclusive) map against that hash from
>> within BPF once it runs. The construction is sound as a trusted hash
>> chain, but the kernel itself never attests the metadata, and that split
>> has been the recurring objection from the LSM / integrity side since the
>> scheme was proposed.
>>
>> This proposal closes both gaps by having the kernel verify the metadata
>> at BPF_PROG_LOAD time, before the LSM admission hook and before the
>> verifier, /without/ growing the UAPI. A signed loader binds its metadata
>> map(s) through the existing fd_array/fd_array_cnt, and exclusive maps
>> are already bound to the loader's digest via excl_prog_hash. When a
>> signature is present, the kernel collects the exclusive maps from the
>> fd_array and appends their frozen contents to the instructions before
>> PKCS#7 verification, so the signature covers ...
>>
>>      insns || metadata_0 || metadata_1 || [...]
>>
>> ... in fd_array order. The in-loader hash check is dropped from the
>> gen_loader entirely: generated loaders carry no verification logic
>> anymore, and signing or verifying a skeleton becomes an ordinary CMS
>> operation over bytes that sit verbatim in the skeleton, reproducible
>> offline. A signed program is either BPF_SIG_UNSIGNED or BPF_SIG_VERIFIED
>> with nothing in between.
>>
>> There is no new UAPI, we now have a single signature scheme, no LSM
>> code reaching into BPF internals, no new LSM hook, and unsigned loads
>> are completely unaffected. It is also less complex since the loader
>> does not need to deal with BTF, an extra kfunc, etc, as proposed in
>> an earlier series [0]. Tested against full BPF CI which came back
>> green. For more details and examples, see the documentation patch in
>> this series.
>>
>>    [0] https://lore.kernel.org/bpf/20260522023234.3778588-1-kpsingh@kernel.org/
>>
>> v3 -> v4:
>>    - Fix upper limit in MAX_FD_ARRAY_CNT (Anton)
>>    - Reject !fd_array && attr->fd_array_cnt (Anton)
>>    - Add bpftool patch wrt ignored return value of EVP_Digest() (sashiko)
>>    - Fix setting of gen_loader_fixture_init (sashiko)
>>    - Fix unused map_fd cleanup branch in selftest (bot+bpf-ci)
>>    - Remove now unused map->excl member and adjust selftests
>>    - Added more BPF signed_loader corner case selftest coverage
>>    - Added Paul's Nack wrt bpf_prog_load LSM hook dispute
>>    - Added patch 2 to move bigger allocations below fd_array
>>      resolution (Paul)
> 
> If you want to squash patch 2/9 and 3/9 together so that one can't
> easily merge 3/9 without the vzalloc(program) relocation I'll gladly
> drop my NACK on patch 3/9.

Okay, I can do that and send a v5. Btw, I saw one sashiko complaint
about the security_bpf_prog_load() internally not needing the:

   [...]
         if (unlikely(rc))
                 security_bpf_prog_free(prog);
   [...]

since the security_bpf_prog_free() is already called via the regular
teardown path now. While there are no in-tree LSM users that are
affected by this, I'll include this as well into the squashed patch,
so its really only called once and not twice.

>> v2 -> v3:
>>    - Added first commit to cache and work on objects in fd_array
>>      which was the most recent issue sashiko rightfully complained
>>    - Added more BPF signed_loader selftest coverage to cover that
>>      usage of sparse fd_array or map fds gets rejected
>>    - I left the security_bpf_prog_load as in v2 given preference
>>      from BPF side over adding new hook
>> v1 -> v2:
>>    - Addressed both sashiko complaints, the TOCTOU bug regarding
>>      fd_array processing, as well as exclusive map checking to
>>      only allow array maps. The validation is now moved into the
>>      verifier before the main verification work happens. This also
>>      gives the opportunity to utilize the verifier log.
>>
>> Daniel Borkmann (9):
>>    bpf: Resolve and cache fd_array objects at load time
>>    bpf: Move bigger allocations below fd_array resolution
>>    bpf: Verify signed loader metadata at load time
>>    libbpf: Drop in-loader metadata check for load-time verification
>>    bpftool: Check EVP_Digest when computing excl_prog_hash
>>    bpftool: Cover loader metadata with the program signature
>>    selftests/bpf: Adjust bpf_map layout in verifier_map_ptr
>>    selftests/bpf: Verify load-time signed loader metadata
>>    Documentation/bpf: Add BPF signing and enforcement doc
>>
>>   Documentation/bpf/index.rst                   |    1 +
>>   Documentation/bpf/signing.rst                 |  496 ++++++++
>>   include/linux/bpf.h                           |    1 -
>>   include/linux/bpf_verifier.h                  |   23 +-
>>   kernel/bpf/syscall.c                          |   83 +-
>>   kernel/bpf/verifier.c                         |  450 ++++++--
>>   tools/bpf/bpftool/gen.c                       |    2 +
>>   tools/bpf/bpftool/sign.c                      |   24 +-
>>   tools/lib/bpf/bpf_gen_internal.h              |    1 -
>>   tools/lib/bpf/gen_loader.c                    |   76 +-
>>   tools/lib/bpf/libbpf_internal.h               |    1 -
>>   tools/lib/bpf/skel_internal.h                 |   31 +-
>>   .../selftests/bpf/prog_tests/signed_loader.c  | 1004 ++++++++++++++---
>>   .../selftests/bpf/progs/test_signed_loader.c  |    9 +-
>>   .../selftests/bpf/progs/verifier_map_ptr.c    |   23 +-
>>   15 files changed, 1786 insertions(+), 439 deletions(-)
>>   create mode 100644 Documentation/bpf/signing.rst

Thanks,
Daniel

Re: [PATCH bpf-next v4 0/9] Verify BPF signed loader at load time

[Paul Moore]

On Mon, Jul 6, 2026 at 1:47 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
> On 7/6/26 7:13 PM, Paul Moore wrote:
> > On Mon, Jul 6, 2026 at 9:56 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
> >>
> >> The BPF signing scheme signs a light skeleton's loader program and lets
> >> the loader vouch for everything else: bpftool bakes the SHA256 of the
> >> metadata map into the loader's instructions, signs the instructions, and
> >> the loader compares the (frozen, exclusive) map against that hash from
> >> within BPF once it runs. The construction is sound as a trusted hash
> >> chain, but the kernel itself never attests the metadata, and that split
> >> has been the recurring objection from the LSM / integrity side since the
> >> scheme was proposed.
> >>
> >> This proposal closes both gaps by having the kernel verify the metadata
> >> at BPF_PROG_LOAD time, before the LSM admission hook and before the
> >> verifier, /without/ growing the UAPI. A signed loader binds its metadata
> >> map(s) through the existing fd_array/fd_array_cnt, and exclusive maps
> >> are already bound to the loader's digest via excl_prog_hash. When a
> >> signature is present, the kernel collects the exclusive maps from the
> >> fd_array and appends their frozen contents to the instructions before
> >> PKCS#7 verification, so the signature covers ...
> >>
> >>      insns || metadata_0 || metadata_1 || [...]
> >>
> >> ... in fd_array order. The in-loader hash check is dropped from the
> >> gen_loader entirely: generated loaders carry no verification logic
> >> anymore, and signing or verifying a skeleton becomes an ordinary CMS
> >> operation over bytes that sit verbatim in the skeleton, reproducible
> >> offline. A signed program is either BPF_SIG_UNSIGNED or BPF_SIG_VERIFIED
> >> with nothing in between.
> >>
> >> There is no new UAPI, we now have a single signature scheme, no LSM
> >> code reaching into BPF internals, no new LSM hook, and unsigned loads
> >> are completely unaffected. It is also less complex since the loader
> >> does not need to deal with BTF, an extra kfunc, etc, as proposed in
> >> an earlier series [0]. Tested against full BPF CI which came back
> >> green. For more details and examples, see the documentation patch in
> >> this series.
> >>
> >>    [0] https://lore.kernel.org/bpf/20260522023234.3778588-1-kpsingh@kernel.org/
> >>
> >> v3 -> v4:
> >>    - Fix upper limit in MAX_FD_ARRAY_CNT (Anton)
> >>    - Reject !fd_array && attr->fd_array_cnt (Anton)
> >>    - Add bpftool patch wrt ignored return value of EVP_Digest() (sashiko)
> >>    - Fix setting of gen_loader_fixture_init (sashiko)
> >>    - Fix unused map_fd cleanup branch in selftest (bot+bpf-ci)
> >>    - Remove now unused map->excl member and adjust selftests
> >>    - Added more BPF signed_loader corner case selftest coverage
> >>    - Added Paul's Nack wrt bpf_prog_load LSM hook dispute
> >>    - Added patch 2 to move bigger allocations below fd_array
> >>      resolution (Paul)
> >
> > If you want to squash patch 2/9 and 3/9 together so that one can't
> > easily merge 3/9 without the vzalloc(program) relocation I'll gladly
> > drop my NACK on patch 3/9.
>
> Okay, I can do that and send a v5.

Great, thanks.

> Btw, I saw one sashiko complaint
> about the security_bpf_prog_load() internally not needing the:
>
>    [...]
>          if (unlikely(rc))
>                  security_bpf_prog_free(prog);
>    [...]
>
> since the security_bpf_prog_free() is already called via the regular
> teardown path now. While there are no in-tree LSM users that are
> affected by this, I'll include this as well into the squashed patch,
> so its really only called once and not twice.

I'd prefer to handle it like it was handled in commit 868d43cf8f97
("bpf: Fix security_bpf_prog_load() error handling").  Since
security_bpf_prog_load() acts not only as an access control point, but
potentially an allocation function as well, I think it is more
consistent in the error case to have the hook do whatever cleanup is
necessary before returning to the caller.

-- 
paul-moore.com