[PATCH v10 0/9] bpf: Add kfuncs for PKCS#7 signature verification

[PATCH v10 0/9] bpf: Add kfuncs for PKCS#7 signature verification

[Roberto Sassu]

One of the desirable features in security is the ability to restrict import
of data to a given system based on data authenticity. If data import can be
restricted, it would be possible to enforce a system-wide policy based on
the signing keys the system owner trusts.

This feature is widely used in the kernel. For example, if the restriction
is enabled, kernel modules can be plugged in only if they are signed with a
key whose public part is in the primary or secondary keyring.

For eBPF, it can be useful as well. For example, it might be useful to
authenticate data an eBPF program makes security decisions on.

After a discussion in the eBPF mailing list, it was decided that the stated
goal should be accomplished by introducing four new kfuncs:
bpf_lookup_user_key() and bpf_lookup_system_key(), for retrieving a keyring
with keys trusted for signature verification, respectively from its serial
and from a pre-determined ID; bpf_key_put(), to release the reference
obtained with the former two kfuncs, bpf_verify_pkcs7_signature(), for
verifying PKCS#7 signatures.

Other than the key serial, bpf_lookup_user_key() also accepts key lookup
flags, that influence the behavior of the lookup. bpf_lookup_system_key()
accepts pre-determined IDs defined in include/linux/verification.h.

bpf_key_put() accepts the new bpf_key structure, introduced to tell whether
the other structure member, a key pointer, is valid or not. The reason is
that verify_pkcs7_signature() also accepts invalid pointers, set with the
pre-determined ID, to select a system-defined keyring. key_put() must be
called only for valid key pointers.

Since the two key lookup functions allocate memory and one increments a key
reference count, they must be used in conjunction with bpf_key_put(). The
latter must be called only if the lookup functions returned a non-NULL
pointer. The verifier denies the execution of eBPF programs that don't
respect this rule.

The two key lookup functions should be used in alternative, depending on
the use case. While bpf_lookup_user_key() provides great flexibility, it
seems suboptimal in terms of security guarantees, as even if the eBPF
program is assumed to be trusted, the serial used to obtain the key pointer
might come from untrusted user space not choosing one that the system
administrator approves to enforce a mandatory policy.

bpf_lookup_system_key() instead provides much stronger guarantees,
especially if the pre-determined ID is not passed by user space but is
hardcoded in the eBPF program, and that program is signed. In this case,
bpf_verify_pkcs7_signature() will always perform signature verification
with a key that the system administrator approves, i.e. the primary,
secondary or platform keyring.

Nevertheless, key permission checks need to be done accurately. Since
bpf_lookup_user_key() cannot determine how a key will be used by other
kfuncs, it has to defer the permission check to the actual kfunc using the
key. It does it by calling lookup_user_key() with KEY_DEFER_PERM_CHECK as
needed permission. Later, bpf_verify_pkcs7_signature(), if called,
completes the permission check by calling key_validate(). It does not need
to call key_task_permission() with permission KEY_NEED_SEARCH, as it is
already done elsewhere by the key subsystem. Future kfuncs using the
bpf_key structure need to implement the proper checks as well.

Finally, the last kfunc, bpf_verify_pkcs7_signature(), accepts the data and
signature to verify as eBPF dynamic pointers, to minimize the number of
kfunc parameters, and the keyring with keys for signature verification as a
bpf_key structure, returned by one of the two key lookup functions.

bpf_lookup_user_key() and bpf_verify_pkcs7_signature() can be called only
from sleepable programs, because of memory allocation and crypto
operations. For example, the lsm.s/bpf attach point is suitable,
fexit/array_map_update_elem is not.

The correctness of implementation of the new kfuncs and of their usage is
checked with the introduced tests.

The patch set includes a patch from another author (dependency) for sake of
completeness. It is organized as follows.

Patch 1 from KP Singh allows kfuncs to be used by LSM programs. Patch 2
allows dynamic pointers to be used as kfunc parameters. Patch 3 exports
bpf_dynptr_get_size(), to obtain the real size of data carried by a dynamic
pointer. Patch 4 makes available for new eBPF kfuncs some key-related
definitions. Patch 5 introduces the bpf_lookup_*_key() and bpf_key_put()
kfuncs. Patch 6 introduces the bpf_verify_pkcs7_signature() kfunc. Finally,
patches 7-9 introduce the tests.

Changelog

v9:
 - Drop patch to introduce KF_SLEEPABLE kfunc flag (already merged)
 - Rename valid_ptr member of bpf_key to has_ref (suggested by Daniel)
 - Check dynamic pointers in kfunc definition with bpf_dynptr_kern struct
   definition instead of string, to detect structure renames (suggested by
   Daniel)
 - Explicitly say that we permit initialized dynamic pointers in kfunc
   definition (suggested by Daniel)
 - Remove noinline __weak from kfuncs definition (reported by Daniel)
 - Simplify key lookup flags check in bpf_lookup_user_key() (suggested by
   Daniel)
 - Explain the reason for deferring key permission check (suggested by
   Daniel)
 - Allocate memory with GFP_ATOMIC in bpf_lookup_system_key(), and remove
   KF_SLEEPABLE kfunc flag from kfunc declaration (suggested by Daniel)
 - Define only one kfunc set and remove the loop for registration
   (suggested by Alexei)

v8:
 - Define the new bpf_key structure to carry the key pointer and whether
   that pointer is valid or not (suggested by Daniel)
 - Drop patch to mark a kfunc parameter with the __maybe_null suffix
 - Improve documentation of kfuncs
 - Introduce bpf_lookup_system_key() to obtain a key pointer suitable for
   verify_pkcs7_signature() (suggested by Daniel)
 - Use the new kfunc registration API
 - Drop patch to test the __maybe_null suffix
 - Add tests for bpf_lookup_system_key()

v7:
 - Add support for using dynamic and NULL pointers in kfunc (suggested by
   Alexei)
 - Add new kfunc-related tests

v6:
 - Switch back to key lookup helpers + signature verification (until v5),
   and defer permission check from bpf_lookup_user_key() to
   bpf_verify_pkcs7_signature()
 - Add additional key lookup test to illustrate the usage of the
   KEY_LOOKUP_CREATE flag and validate the flags (suggested by Daniel)
 - Make description of flags of bpf_lookup_user_key() more user-friendly
   (suggested by Daniel)
 - Fix validation of flags parameter in bpf_lookup_user_key() (reported by
   Daniel)
 - Rename bpf_verify_pkcs7_signature() keyring-related parameters to
   user_keyring and system_keyring to make their purpose more clear
 - Accept keyring-related parameters of bpf_verify_pkcs7_signature() as
   alternatives (suggested by KP)
 - Replace unsigned long type with u64 in helper declaration (suggested by
   Daniel)
 - Extend the bpf_verify_pkcs7_signature() test by calling the helper
   without data, by ensuring that the helper enforces the keyring-related
   parameters as alternatives, by ensuring that the helper rejects
   inaccessible and expired keyrings, and by checking all system keyrings
 - Move bpf_lookup_user_key() and bpf_key_put() usage tests to
   ref_tracking.c (suggested by John)
 - Call bpf_lookup_user_key() and bpf_key_put() only in sleepable programs

v5:
 - Move KEY_LOOKUP_ to include/linux/key.h
   for validation of bpf_verify_pkcs7_signature() parameter
 - Remove bpf_lookup_user_key() and bpf_key_put() helpers, and the
   corresponding tests
 - Replace struct key parameter of bpf_verify_pkcs7_signature() with the
   keyring serial and lookup flags
 - Call lookup_user_key() and key_put() in bpf_verify_pkcs7_signature()
   code, to ensure that the retrieved key is used according to the
   permission requested at lookup time
 - Clarified keyring precedence in the description of
   bpf_verify_pkcs7_signature() (suggested by John)
 - Remove newline in the second argument of ASSERT_
 - Fix helper prototype regular expression in bpf_doc.py

v4:
 - Remove bpf_request_key_by_id(), don't return an invalid pointer that
   other helpers can use
 - Pass the keyring ID (without ULONG_MAX, suggested by Alexei) to
   bpf_verify_pkcs7_signature()
 - Introduce bpf_lookup_user_key() and bpf_key_put() helpers (suggested by
   Alexei)
 - Add lookup_key_norelease test, to ensure that the verifier blocks eBPF
   programs which don't decrement the key reference count
 - Parse raw PKCS#7 signature instead of module-style signature in the
   verify_pkcs7_signature test (suggested by Alexei)
 - Parse kernel module in user space and pass raw PKCS#7 signature to the
   eBPF program for signature verification

v3:
 - Rename bpf_verify_signature() back to bpf_verify_pkcs7_signature() to
   avoid managing different parameters for each signature verification
   function in one helper (suggested by Daniel)
 - Use dynamic pointers and export bpf_dynptr_get_size() (suggested by
   Alexei)
 - Introduce bpf_request_key_by_id() to give more flexibility to the caller
   of bpf_verify_pkcs7_signature() to retrieve the appropriate keyring
   (suggested by Alexei)
 - Fix test by reordering the gcc command line, always compile sign-file
 - Improve helper support check mechanism in the test

v2:
 - Rename bpf_verify_pkcs7_signature() to a more generic
   bpf_verify_signature() and pass the signature type (suggested by KP)
 - Move the helper and prototype declaration under #ifdef so that user
   space can probe for support for the helper (suggested by Daniel)
 - Describe better the keyring types (suggested by Daniel)
 - Include linux/bpf.h instead of vmlinux.h to avoid implicit or
   redeclaration
 - Make the test selfcontained (suggested by Alexei)

v1:
 - Don't define new map flag but introduce simple wrapper of
   verify_pkcs7_signature() (suggested by Alexei and KP)

KP Singh (1):
  bpf: Allow kfuncs to be used in LSM programs

Roberto Sassu (8):
  btf: Handle dynamic pointer parameter in kfuncs
  bpf: Export bpf_dynptr_get_size()
  KEYS: Move KEY_LOOKUP_ to include/linux/key.h
  bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs
  bpf: Add bpf_verify_pkcs7_signature() kfunc
  selftests/bpf: Add verifier tests for bpf_lookup_*_key() and
    bpf_key_put()
  selftests/bpf: Add additional tests for bpf_lookup_*_key()
  selftests/bpf: Add test for bpf_verify_pkcs7_signature() kfunc

 include/linux/bpf.h                           |   7 +
 include/linux/bpf_verifier.h                  |   3 +
 include/linux/key.h                           |   3 +
 kernel/bpf/btf.c                              |  23 +
 kernel/bpf/helpers.c                          |   2 +-
 kernel/bpf/verifier.c                         |   4 +-
 kernel/trace/bpf_trace.c                      | 191 +++++++++
 security/keys/internal.h                      |   2 -
 tools/testing/selftests/bpf/Makefile          |  14 +-
 tools/testing/selftests/bpf/config            |   2 +
 .../selftests/bpf/prog_tests/lookup_key.c     | 112 +++++
 .../bpf/prog_tests/verify_pkcs7_sig.c         | 399 ++++++++++++++++++
 .../selftests/bpf/progs/test_lookup_key.c     |  46 ++
 .../bpf/progs/test_verify_pkcs7_sig.c         | 100 +++++
 tools/testing/selftests/bpf/test_verifier.c   |   3 +-
 .../selftests/bpf/verifier/ref_tracking.c     | 139 ++++++
 .../testing/selftests/bpf/verify_sig_setup.sh | 104 +++++
 17 files changed, 1145 insertions(+), 9 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/lookup_key.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/verify_pkcs7_sig.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_lookup_key.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_verify_pkcs7_sig.c
 create mode 100755 tools/testing/selftests/bpf/verify_sig_setup.sh

-- 
2.25.1

[PATCH v10 1/9] bpf: Allow kfuncs to be used in LSM programs

[Roberto Sassu]

From: KP Singh <kpsingh@kernel.org>

In preparation for the addition of new kfuncs, allow kfuncs defined in the
tracing subsystem to be used in LSM programs by mapping the LSM program
type to the TRACING hook.

Signed-off-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 kernel/bpf/btf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 903719b89238..e49b3b6d48ad 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7243,6 +7243,7 @@ static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
 	case BPF_PROG_TYPE_STRUCT_OPS:
 		return BTF_KFUNC_HOOK_STRUCT_OPS;
 	case BPF_PROG_TYPE_TRACING:
+	case BPF_PROG_TYPE_LSM:
 		return BTF_KFUNC_HOOK_TRACING;
 	case BPF_PROG_TYPE_SYSCALL:
 		return BTF_KFUNC_HOOK_SYSCALL;
-- 
2.25.1

[PATCH v10 2/9] btf: Handle dynamic pointer parameter in kfuncs

[Roberto Sassu]

Allow the bpf_dynptr_kern parameter to be specified in kfuncs. Also, ensure
that the dynamic pointer is valid and initialized.

Cc: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/bpf_verifier.h |  3 +++
 kernel/bpf/btf.c             | 22 ++++++++++++++++++++++
 kernel/bpf/verifier.c        |  4 ++--
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 2e3bad8640dc..55876fbdbae2 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -560,6 +560,9 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state
 			     u32 regno);
 int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 		   u32 regno, u32 mem_size);
+bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
+			      struct bpf_reg_state *reg,
+			      enum bpf_arg_type arg_type);
 
 /* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
 static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index e49b3b6d48ad..86e63f2ee5da 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -195,6 +195,10 @@
 	     i < btf_type_vlen(struct_type);					\
 	     i++, member++)
 
+#define stringify_struct(x)			\
+	({ BUILD_BUG_ON(sizeof(struct x) < 0);	\
+	   __stringify(x); })
+
 DEFINE_IDR(btf_idr);
 DEFINE_SPINLOCK(btf_idr_lock);
 
@@ -6362,15 +6366,20 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 
 			if (is_kfunc) {
 				bool arg_mem_size = i + 1 < nargs && is_kfunc_arg_mem_size(btf, &args[i + 1], &regs[regno + 1]);
+				bool arg_dynptr = btf_type_is_struct(ref_t) &&
+						  !strcmp(ref_tname,
+							  stringify_struct(bpf_dynptr_kern));
 
 				/* Permit pointer to mem, but only when argument
 				 * type is pointer to scalar, or struct composed
 				 * (recursively) of scalars.
 				 * When arg_mem_size is true, the pointer can be
 				 * void *.
+				 * Also permit initialized dynamic pointers.
 				 */
 				if (!btf_type_is_scalar(ref_t) &&
 				    !__btf_type_is_scalar_struct(log, btf, ref_t, 0) &&
+				    !arg_dynptr &&
 				    (arg_mem_size ? !btf_type_is_void(ref_t) : 1)) {
 					bpf_log(log,
 						"arg#%d pointer type %s %s must point to %sscalar, or struct with scalar\n",
@@ -6378,6 +6387,19 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 					return -EINVAL;
 				}
 
+				if (arg_dynptr) {
+					if (!is_dynptr_reg_valid_init(env, reg,
+							ARG_PTR_TO_DYNPTR)) {
+						bpf_log(log,
+							"arg#%d pointer type %s %s must be initialized\n",
+							i, btf_type_str(ref_t),
+							ref_tname);
+						return -EINVAL;
+					}
+
+					continue;
+				}
+
 				/* Check for mem, len pair */
 				if (arg_mem_size) {
 					if (check_kfunc_mem_size_reg(env, &regs[regno + 1], regno + 1)) {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2c1f8069f7b7..aa834e7bb296 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -779,8 +779,8 @@ static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_
 	return true;
 }
 
-static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
-				     enum bpf_arg_type arg_type)
+bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+			      enum bpf_arg_type arg_type)
 {
 	struct bpf_func_state *state = func(env, reg);
 	int spi = get_spi(reg->off);
-- 
2.25.1

[PATCH v10 3/9] bpf: Export bpf_dynptr_get_size()

[Roberto Sassu]

Export bpf_dynptr_get_size(), so that kernel code dealing with eBPF dynamic
pointers can obtain the real size of data carried by this data structure.

Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/bpf.h  | 1 +
 kernel/bpf/helpers.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a627a02cf8ab..a82f8c559ae2 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2563,6 +2563,7 @@ void bpf_dynptr_init(struct bpf_dynptr_kern *ptr, void *data,
 		     enum bpf_dynptr_type type, u32 offset, u32 size);
 void bpf_dynptr_set_null(struct bpf_dynptr_kern *ptr);
 int bpf_dynptr_check_size(u32 size);
+u32 bpf_dynptr_get_size(struct bpf_dynptr_kern *ptr);
 
 #ifdef CONFIG_BPF_LSM
 void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype);
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 3c1b9bbcf971..e4637ccb3016 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1442,7 +1442,7 @@ static void bpf_dynptr_set_type(struct bpf_dynptr_kern *ptr, enum bpf_dynptr_typ
 	ptr->size |= type << DYNPTR_TYPE_SHIFT;
 }
 
-static u32 bpf_dynptr_get_size(struct bpf_dynptr_kern *ptr)
+u32 bpf_dynptr_get_size(struct bpf_dynptr_kern *ptr)
 {
 	return ptr->size & DYNPTR_SIZE_MASK;
 }
-- 
2.25.1

[PATCH v10 4/9] KEYS: Move KEY_LOOKUP_ to include/linux/key.h

[Roberto Sassu]

In preparation for the patch that introduces the bpf_lookup_user_key() eBPF
kfunc, move KEY_LOOKUP_ definitions to include/linux/key.h, to be able to
validate the kfunc parameters.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/key.h      | 3 +++
 security/keys/internal.h | 2 --
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/key.h b/include/linux/key.h
index 7febc4881363..a297e075038c 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -88,6 +88,9 @@ enum key_need_perm {
 	KEY_DEFER_PERM_CHECK,	/* Special: permission check is deferred */
 };
 
+#define KEY_LOOKUP_CREATE	0x01
+#define KEY_LOOKUP_PARTIAL	0x02
+
 struct seq_file;
 struct user_struct;
 struct signal_struct;
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 9b9cf3b6fcbb..3c1e7122076b 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -165,8 +165,6 @@ extern struct key *request_key_and_link(struct key_type *type,
 
 extern bool lookup_user_key_possessed(const struct key *key,
 				      const struct key_match_data *match_data);
-#define KEY_LOOKUP_CREATE	0x01
-#define KEY_LOOKUP_PARTIAL	0x02
 
 extern long join_session_keyring(const char *name);
 extern void key_change_session_keyring(struct callback_head *twork);
-- 
2.25.1

[PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Roberto Sassu]

Add the bpf_lookup_user_key(), bpf_lookup_system_key() and bpf_key_put()
kfuncs, to respectively search a key with a given serial and flags, obtain
a key from a pre-determined ID defined in include/linux/verification.h, and
cleanup.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/bpf.h      |   6 ++
 kernel/trace/bpf_trace.c | 146 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 152 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a82f8c559ae2..d415e5e97551 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2573,4 +2573,10 @@ static inline void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype) {}
 static inline void bpf_cgroup_atype_put(int cgroup_atype) {}
 #endif /* CONFIG_BPF_LSM */
 
+#ifdef CONFIG_KEYS
+struct bpf_key {
+	struct key *key;
+	bool has_ref;
+};
+#endif /* CONFIG_KEYS */
 #endif /* _LINUX_BPF_H */
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 68e5cdd24cef..a607bb0be738 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -20,6 +20,8 @@
 #include <linux/fprobe.h>
 #include <linux/bsearch.h>
 #include <linux/sort.h>
+#include <linux/key.h>
+#include <linux/verification.h>
 
 #include <net/bpf_sk_storage.h>
 
@@ -1181,6 +1183,150 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = {
 	.arg1_type	= ARG_PTR_TO_CTX,
 };
 
+#ifdef CONFIG_KEYS
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+		  "kfuncs which will be used in BPF programs");
+
+/**
+ * bpf_lookup_user_key - lookup a key by its serial
+ * @serial: key serial
+ * @flags: lookup-specific flags
+ *
+ * Search a key with a given *serial* and the provided *flags*. The
+ * returned key, if found, has the reference count incremented by
+ * one, and is stored in a bpf_key structure, returned to the caller.
+ * The bpf_key structure must be passed to bpf_key_put() when done
+ * with it, so that the key reference count is decremented and the
+ * bpf_key structure is freed.
+ *
+ * Permission checks are deferred to the time the key is used by
+ * one of the available key-specific kfuncs.
+ *
+ * Set *flags* with 1, to attempt creating a requested special
+ * keyring (e.g. session keyring), if it doesn't yet exist. Set
+ * *flags* with 2 to lookup a key without waiting for the key
+ * construction, and to retrieve uninstantiated keys (keys without
+ * data attached to them).
+ *
+ * Return: a bpf_key pointer with a valid key pointer if the key is found, a
+ *         NULL pointer otherwise.
+ */
+struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags)
+{
+	key_ref_t key_ref;
+	struct bpf_key *bkey;
+
+	/* Keep in sync with include/linux/key.h. */
+	if (flags & ~(KEY_LOOKUP_CREATE | KEY_LOOKUP_PARTIAL))
+		return NULL;
+
+	/*
+	 * Permission check is deferred until actual kfunc using the key,
+	 * since here the intent of the caller is not yet known.
+	 *
+	 * We cannot trust the caller to provide the needed permission as
+	 * argument, since nothing prevents the caller from using the
+	 * obtained key for a different purpose than the one declared.
+	 */
+	key_ref = lookup_user_key(serial, flags, KEY_DEFER_PERM_CHECK);
+	if (IS_ERR(key_ref))
+		return NULL;
+
+	bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC);
+	if (!bkey) {
+		key_put(key_ref_to_ptr(key_ref));
+		return NULL;
+	}
+
+	bkey->key = key_ref_to_ptr(key_ref);
+	bkey->has_ref = true;
+
+	return bkey;
+}
+
+/**
+ * bpf_lookup_system_key - lookup a key by a system-defined ID
+ * @id: key ID
+ *
+ * Obtain a bpf_key structure with a key pointer set to the passed key ID.
+ * The key pointer is marked as invalid, to prevent bpf_key_put() from
+ * attempting to decrement the key reference count on that pointer. The key
+ * pointer set in such way is currently understood only by
+ * verify_pkcs7_signature().
+ *
+ * Set *id* to one of the values defined in include/linux/verification.h:
+ * 0 for the primary keyring (immutable keyring of system keys); 1 for both
+ * the primary and secondary keyring (where keys can be added only if they
+ * are vouched for by existing keys in those keyrings); 2 for the platform
+ * keyring (primarily used by the integrity subsystem to verify a kexec'ed
+ * kerned image and, possibly, the initramfs signature).
+ *
+ * Return: a bpf_key pointer with an invalid key pointer set from the
+ *         pre-determined ID on success, a NULL pointer otherwise
+ */
+struct bpf_key *bpf_lookup_system_key(u64 id)
+{
+	struct bpf_key *bkey;
+
+	/* Keep in sync with defs in include/linux/verification.h. */
+	if (id > (unsigned long)VERIFY_USE_PLATFORM_KEYRING)
+		return NULL;
+
+	bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC);
+	if (!bkey)
+		return NULL;
+
+	bkey->key = (struct key *)(unsigned long)id;
+	bkey->has_ref = false;
+
+	return bkey;
+}
+
+/**
+ * bpf_key_put - decrement key reference count if key is valid and free bpf_key
+ * @bkey: bpf_key structure
+ *
+ * Decrement the reference count of the key inside *bkey*, if the pointer
+ * is valid, and free *bkey*.
+ */
+void bpf_key_put(struct bpf_key *bkey)
+{
+	if (bkey->has_ref)
+		key_put(bkey->key);
+
+	kfree(bkey);
+}
+
+__diag_pop();
+
+BTF_SET8_START(key_sig_kfunc_set)
+BTF_ID_FLAGS(func, bpf_lookup_user_key, KF_ACQUIRE | KF_RET_NULL | KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_lookup_system_key, KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_key_put, KF_RELEASE)
+BTF_SET8_END(key_sig_kfunc_set)
+
+static const struct btf_kfunc_id_set bpf_key_sig_kfunc_set = {
+	.owner = THIS_MODULE,
+	.set = &key_sig_kfunc_set,
+};
+
+static int __init bpf_key_sig_kfuncs_init(void)
+{
+	int ret;
+
+	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
+					&bpf_key_sig_kfunc_set);
+	if (!ret)
+		return 0;
+
+	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
+					 &bpf_key_sig_kfunc_set);
+}
+
+late_initcall(bpf_key_sig_kfuncs_init);
+#endif /* CONFIG_KEYS */
+
 static const struct bpf_func_proto *
 bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
-- 
2.25.1

[PATCH v10 6/9] bpf: Add bpf_verify_pkcs7_signature() kfunc

[Roberto Sassu]

Add the bpf_verify_pkcs7_signature() kfunc, to give eBPF security modules
the ability to check the validity of a signature against supplied data, by
using user-provided or system-provided keys as trust anchor.

The new kfunc makes it possible to enforce mandatory policies, as eBPF
programs might be allowed to make security decisions only based on data
sources the system administrator approves.

The caller should provide the data to be verified and the signature as eBPF
dynamic pointers (to minimize the number of parameters) and a bpf_key
structure containing a reference to the keyring with keys trusted for
signature verification, obtained from bpf_lookup_user_key() or
bpf_lookup_system_key().

For bpf_key structures obtained from the former lookup function,
bpf_verify_pkcs7_signature() completes the permission check deferred by
that function by calling key_validate(). key_task_permission() is already
called by the PKCS#7 code.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 kernel/trace/bpf_trace.c | 45 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a607bb0be738..d575e026e698 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1298,12 +1298,57 @@ void bpf_key_put(struct bpf_key *bkey)
 	kfree(bkey);
 }
 
+#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
+/**
+ * bpf_verify_pkcs7_signature - verify a PKCS#7 signature
+ * @data_ptr: data to verify
+ * @sig_ptr: signature of the data
+ * @trusted_keyring: keyring with keys trusted for signature verification
+ *
+ * Verify the PKCS#7 signature *sig_ptr* against the supplied *data_ptr*
+ * with keys in a keyring referenced by *trusted_keyring*.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
+			       struct bpf_dynptr_kern *sig_ptr,
+			       struct bpf_key *trusted_keyring)
+{
+	int ret;
+
+	if (trusted_keyring->has_ref) {
+		/*
+		 * Do the permission check deferred in bpf_lookup_user_key().
+		 * See bpf_lookup_user_key() for more details.
+		 *
+		 * A call to key_task_permission() here would be redundant, as
+		 * it is already done by keyring_search() called by
+		 * find_asymmetric_key().
+		 */
+		ret = key_validate(trusted_keyring->key);
+		if (ret < 0)
+			return ret;
+	}
+
+	return verify_pkcs7_signature(data_ptr->data,
+				      bpf_dynptr_get_size(data_ptr),
+				      sig_ptr->data,
+				      bpf_dynptr_get_size(sig_ptr),
+				      trusted_keyring->key,
+				      VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
+				      NULL);
+}
+#endif /* CONFIG_SYSTEM_DATA_VERIFICATION */
+
 __diag_pop();
 
 BTF_SET8_START(key_sig_kfunc_set)
 BTF_ID_FLAGS(func, bpf_lookup_user_key, KF_ACQUIRE | KF_RET_NULL | KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_lookup_system_key, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_key_put, KF_RELEASE)
+#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
+BTF_ID_FLAGS(func, bpf_verify_pkcs7_signature, KF_SLEEPABLE)
+#endif
 BTF_SET8_END(key_sig_kfunc_set)
 
 static const struct btf_kfunc_id_set bpf_key_sig_kfunc_set = {
-- 
2.25.1

[PATCH v10 7/9] selftests/bpf: Add verifier tests for bpf_lookup_*_key() and bpf_key_put()

[Roberto Sassu]

Add verifier tests for bpf_lookup_*_key() and bpf_key_put(), to ensure that
acquired key references stored in the bpf_key structure are released, that
a non-NULL bpf_key pointer is passed to bpf_key_put(), and that key
references are not leaked.

Also, slightly modify test_verifier.c, to find the BTF ID of the attach
point for the LSM program type (currently, it is done only for TRACING).

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 tools/testing/selftests/bpf/test_verifier.c   |   3 +-
 .../selftests/bpf/verifier/ref_tracking.c     | 139 ++++++++++++++++++
 2 files changed, 141 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index f9d553fbf68a..2dbcbf363c18 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -1498,7 +1498,8 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 		opts.log_level = DEFAULT_LIBBPF_LOG_LEVEL;
 	opts.prog_flags = pflags;
 
-	if (prog_type == BPF_PROG_TYPE_TRACING && test->kfunc) {
+	if ((prog_type == BPF_PROG_TYPE_TRACING ||
+	     prog_type == BPF_PROG_TYPE_LSM) && test->kfunc) {
 		int attach_btf_id;
 
 		attach_btf_id = libbpf_find_vmlinux_btf_id(test->kfunc,
diff --git a/tools/testing/selftests/bpf/verifier/ref_tracking.c b/tools/testing/selftests/bpf/verifier/ref_tracking.c
index 57a83d763ec1..f18ce867271f 100644
--- a/tools/testing/selftests/bpf/verifier/ref_tracking.c
+++ b/tools/testing/selftests/bpf/verifier/ref_tracking.c
@@ -84,6 +84,145 @@
 	.errstr = "Unreleased reference",
 	.result = REJECT,
 },
+{
+	"reference tracking: acquire/release user key reference",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_1, -3),
+	BPF_MOV64_IMM(BPF_REG_2, 0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_LSM,
+	.kfunc = "bpf",
+	.expected_attach_type = BPF_LSM_MAC,
+	.flags = BPF_F_SLEEPABLE,
+	.fixup_kfunc_btf_id = {
+		{ "bpf_lookup_user_key", 2 },
+		{ "bpf_key_put", 5 },
+	},
+	.result = ACCEPT,
+},
+{
+	"reference tracking: acquire/release system key reference",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_1, 1),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_LSM,
+	.kfunc = "bpf",
+	.expected_attach_type = BPF_LSM_MAC,
+	.flags = BPF_F_SLEEPABLE,
+	.fixup_kfunc_btf_id = {
+		{ "bpf_lookup_system_key", 1 },
+		{ "bpf_key_put", 4 },
+	},
+	.result = ACCEPT,
+},
+{
+	"reference tracking: release user key reference without check",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_1, -3),
+	BPF_MOV64_IMM(BPF_REG_2, 0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_LSM,
+	.kfunc = "bpf",
+	.expected_attach_type = BPF_LSM_MAC,
+	.flags = BPF_F_SLEEPABLE,
+	.errstr = "arg#0 pointer type STRUCT bpf_key must point to scalar, or struct with scalar",
+	.fixup_kfunc_btf_id = {
+		{ "bpf_lookup_user_key", 2 },
+		{ "bpf_key_put", 4 },
+	},
+	.result = REJECT,
+},
+{
+	"reference tracking: release system key reference without check",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_1, 1),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_LSM,
+	.kfunc = "bpf",
+	.expected_attach_type = BPF_LSM_MAC,
+	.flags = BPF_F_SLEEPABLE,
+	.errstr = "arg#0 pointer type STRUCT bpf_key must point to scalar, or struct with scalar",
+	.fixup_kfunc_btf_id = {
+		{ "bpf_lookup_system_key", 1 },
+		{ "bpf_key_put", 3 },
+	},
+	.result = REJECT,
+},
+{
+	"reference tracking: release with NULL key pointer",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_1, 0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_LSM,
+	.kfunc = "bpf",
+	.expected_attach_type = BPF_LSM_MAC,
+	.flags = BPF_F_SLEEPABLE,
+	.errstr = "arg#0 pointer type STRUCT bpf_key must point to scalar, or struct with scalar",
+	.fixup_kfunc_btf_id = {
+		{ "bpf_key_put", 1 },
+	},
+	.result = REJECT,
+},
+{
+	"reference tracking: leak potential reference to user key",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_1, -3),
+	BPF_MOV64_IMM(BPF_REG_2, 0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_LSM,
+	.kfunc = "bpf",
+	.expected_attach_type = BPF_LSM_MAC,
+	.flags = BPF_F_SLEEPABLE,
+	.errstr = "Unreleased reference",
+	.fixup_kfunc_btf_id = {
+		{ "bpf_lookup_user_key", 2 },
+	},
+	.result = REJECT,
+},
+{
+	"reference tracking: leak potential reference to system key",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_1, 1),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_LSM,
+	.kfunc = "bpf",
+	.expected_attach_type = BPF_LSM_MAC,
+	.flags = BPF_F_SLEEPABLE,
+	.errstr = "Unreleased reference",
+	.fixup_kfunc_btf_id = {
+		{ "bpf_lookup_system_key", 1 },
+	},
+	.result = REJECT,
+},
 {
 	"reference tracking: release reference without check",
 	.insns = {
-- 
2.25.1

[PATCH v10 8/9] selftests/bpf: Add additional tests for bpf_lookup_*_key()

[Roberto Sassu]

Add a test to ensure that bpf_lookup_user_key() creates a referenced
special keyring when the KEY_LOOKUP_CREATE flag is passed to this function.

Ensure that the kfunc rejects invalid flags.

Ensure that a keyring can be obtained from bpf_lookup_system_key() when one
of the pre-determined keyring IDs is provided.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 .../selftests/bpf/prog_tests/lookup_key.c     | 112 ++++++++++++++++++
 .../selftests/bpf/progs/test_lookup_key.c     |  46 +++++++
 2 files changed, 158 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/lookup_key.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_lookup_key.c

diff --git a/tools/testing/selftests/bpf/prog_tests/lookup_key.c b/tools/testing/selftests/bpf/prog_tests/lookup_key.c
new file mode 100644
index 000000000000..2e0cde729dc7
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/lookup_key.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ */
+
+#include <linux/keyctl.h>
+#include <test_progs.h>
+
+#include "test_lookup_key.skel.h"
+
+#define KEY_LOOKUP_CREATE	0x01
+#define KEY_LOOKUP_PARTIAL	0x02
+
+static bool kfunc_not_supported;
+
+static int libbpf_print_cb(enum libbpf_print_level level, const char *fmt,
+			   va_list args)
+{
+	char *func;
+
+	if (strcmp(fmt, "libbpf: extern (func ksym) '%s': not found in kernel or module BTFs\n"))
+		return 0;
+
+	func = va_arg(args, char *);
+
+	if (strcmp(func, "bpf_lookup_user_key") && strcmp(func, "bpf_key_put") &&
+	    strcmp(func, "bpf_lookup_system_key"))
+		return 0;
+
+	kfunc_not_supported = true;
+	return 0;
+}
+
+void test_lookup_key(void)
+{
+	libbpf_print_fn_t old_print_cb;
+	struct test_lookup_key *skel;
+	u32 next_id;
+	int ret;
+
+	skel = test_lookup_key__open();
+	if (!ASSERT_OK_PTR(skel, "test_lookup_key__open"))
+		return;
+
+	old_print_cb = libbpf_set_print(libbpf_print_cb);
+	ret = test_lookup_key__load(skel);
+	libbpf_set_print(old_print_cb);
+
+	if (ret < 0 && kfunc_not_supported) {
+		printf("%s:SKIP:bpf_lookup_*_key(), bpf_key_put() kfuncs not supported\n",
+		       __func__);
+		test__skip();
+		goto close_prog;
+	}
+
+	if (!ASSERT_OK(ret, "test_lookup_key__load"))
+		goto close_prog;
+
+	ret = test_lookup_key__attach(skel);
+	if (!ASSERT_OK(ret, "test_lookup_key__attach"))
+		goto close_prog;
+
+	skel->bss->monitored_pid = getpid();
+	skel->bss->key_serial = KEY_SPEC_THREAD_KEYRING;
+
+	/* The thread-specific keyring does not exist, this test fails. */
+	skel->bss->flags = 0;
+
+	ret = bpf_prog_get_next_id(0, &next_id);
+	if (!ASSERT_LT(ret, 0, "bpf_prog_get_next_id"))
+		goto close_prog;
+
+	/* Force creation of the thread-specific keyring, this test succeeds. */
+	skel->bss->flags = KEY_LOOKUP_CREATE;
+
+	ret = bpf_prog_get_next_id(0, &next_id);
+	if (!ASSERT_OK(ret, "bpf_prog_get_next_id"))
+		goto close_prog;
+
+	/* Pass both lookup flags for parameter validation. */
+	skel->bss->flags = KEY_LOOKUP_CREATE | KEY_LOOKUP_PARTIAL;
+
+	ret = bpf_prog_get_next_id(0, &next_id);
+	if (!ASSERT_OK(ret, "bpf_prog_get_next_id"))
+		goto close_prog;
+
+	/* Pass invalid flags. */
+	skel->bss->flags = UINT64_MAX;
+
+	ret = bpf_prog_get_next_id(0, &next_id);
+	if (!ASSERT_LT(ret, 0, "bpf_prog_get_next_id"))
+		goto close_prog;
+
+	skel->bss->key_serial = 0;
+	skel->bss->key_id = 1;
+
+	ret = bpf_prog_get_next_id(0, &next_id);
+	if (!ASSERT_OK(ret, "bpf_prog_get_next_id"))
+		goto close_prog;
+
+	skel->bss->key_id = UINT32_MAX;
+
+	ret = bpf_prog_get_next_id(0, &next_id);
+	ASSERT_LT(ret, 0, "bpf_prog_get_next_id");
+
+close_prog:
+	skel->bss->monitored_pid = 0;
+	test_lookup_key__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_lookup_key.c b/tools/testing/selftests/bpf/progs/test_lookup_key.c
new file mode 100644
index 000000000000..c73776990ae3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_lookup_key.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ */
+
+#include "vmlinux.h"
+#include <errno.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+__u32 monitored_pid;
+__u32 key_serial;
+__u32 key_id;
+__u64 flags;
+
+extern struct bpf_key *bpf_lookup_user_key(__u32 serial, __u64 flags) __ksym;
+extern struct bpf_key *bpf_lookup_system_key(__u64 id) __ksym;
+extern void bpf_key_put(struct bpf_key *key) __ksym;
+
+SEC("lsm.s/bpf")
+int BPF_PROG(bpf, int cmd, union bpf_attr *attr, unsigned int size)
+{
+	struct bpf_key *bkey;
+	__u32 pid;
+
+	pid = bpf_get_current_pid_tgid() >> 32;
+	if (pid != monitored_pid)
+		return 0;
+
+	if (key_serial)
+		bkey = bpf_lookup_user_key(key_serial, flags);
+	else
+		bkey = bpf_lookup_system_key(key_id);
+
+	if (!bkey)
+		return -ENOENT;
+
+	bpf_key_put(bkey);
+
+	return 0;
+}
-- 
2.25.1

[PATCH v10 9/9] selftests/bpf: Add test for bpf_verify_pkcs7_signature() kfunc

[Roberto Sassu]

Perform several tests to ensure the correct implementation of the
bpf_verify_pkcs7_signature() kfunc.

Do the tests with data signed with a generated testing key (by using
sign-file from scripts/) and with the tcp_bic.ko kernel module if it is
found in the system. The test does not fail if tcp_bic.ko is not found.

First, perform an unsuccessful signature verification without data.

Second, perform a successful signature verification with the session
keyring and a new one created for testing.

Then, ensure that permission and validation checks are done properly on the
keyring provided to bpf_verify_pkcs7_signature(), despite those checks were
deferred at the time the keyring was retrieved with bpf_lookup_user_key().
The tests expect to encounter an error if the Search permission is removed
from the keyring, or the keyring is expired.

Finally, perform a successful and unsuccessful signature verification with
the keyrings with pre-determined IDs (the last test fails because the key
is not in the platform keyring).

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 tools/testing/selftests/bpf/Makefile          |  14 +-
 tools/testing/selftests/bpf/config            |   2 +
 .../bpf/prog_tests/verify_pkcs7_sig.c         | 399 ++++++++++++++++++
 .../bpf/progs/test_verify_pkcs7_sig.c         | 100 +++++
 .../testing/selftests/bpf/verify_sig_setup.sh | 104 +++++
 5 files changed, 616 insertions(+), 3 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/verify_pkcs7_sig.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_verify_pkcs7_sig.c
 create mode 100755 tools/testing/selftests/bpf/verify_sig_setup.sh

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 8d59ec7f4c2d..5ae079e276b3 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -14,6 +14,7 @@ BPFTOOLDIR := $(TOOLSDIR)/bpf/bpftool
 APIDIR := $(TOOLSINCDIR)/uapi
 GENDIR := $(abspath ../../../../include/generated)
 GENHDR := $(GENDIR)/autoconf.h
+HOSTPKG_CONFIG := pkg-config
 
 ifneq ($(wildcard $(GENHDR)),)
   GENFLAGS := -DHAVE_GENHDR
@@ -75,7 +76,7 @@ TEST_PROGS := test_kmod.sh \
 	test_xsk.sh
 
 TEST_PROGS_EXTENDED := with_addr.sh \
-	with_tunnels.sh ima_setup.sh \
+	with_tunnels.sh ima_setup.sh verify_sig_setup.sh \
 	test_xdp_vlan.sh test_bpftool.py
 
 # Compile but not part of 'make run_tests'
@@ -84,7 +85,7 @@ TEST_GEN_PROGS_EXTENDED = test_sock_addr test_skb_cgroup_id_user \
 	test_lirc_mode2_user xdping test_cpp runqslower bench bpf_testmod.ko \
 	xskxceiver xdp_redirect_multi xdp_synproxy
 
-TEST_CUSTOM_PROGS = $(OUTPUT)/urandom_read
+TEST_CUSTOM_PROGS = $(OUTPUT)/urandom_read $(OUTPUT)/sign-file
 
 # Emit succinct information message describing current building step
 # $1 - generic step name (e.g., CC, LINK, etc);
@@ -189,6 +190,12 @@ $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_r
 		     -fuse-ld=$(LLD) -Wl,-znoseparate-code		       \
 		     -Wl,-rpath=. -Wl,--build-id=sha1 -o $@
 
+$(OUTPUT)/sign-file: ../../../../scripts/sign-file.c
+	$(call msg,SIGN-FILE,,$@)
+	$(Q)$(CC) $(shell $(HOSTPKG_CONFIG)--cflags libcrypto 2> /dev/null) \
+		  $< -o $@ \
+		  $(shell $(HOSTPKG_CONFIG) --libs libcrypto 2> /dev/null || echo -lcrypto)
+
 $(OUTPUT)/bpf_testmod.ko: $(VMLINUX_BTF) $(wildcard bpf_testmod/Makefile bpf_testmod/*.[ch])
 	$(call msg,MOD,,$@)
 	$(Q)$(RM) bpf_testmod/bpf_testmod.ko # force re-compilation
@@ -514,7 +521,8 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
 TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko	\
 		       $(OUTPUT)/liburandom_read.so			\
 		       $(OUTPUT)/xdp_synproxy				\
-		       ima_setup.sh					\
+		       $(OUTPUT)/sign-file				\
+		       ima_setup.sh verify_sig_setup.sh			\
 		       $(wildcard progs/btf_dump_test_case_*.c)
 TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
 TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) -DENABLE_ATOMICS_TESTS
diff --git a/tools/testing/selftests/bpf/config b/tools/testing/selftests/bpf/config
index fabf0c014349..4d0e4ed20159 100644
--- a/tools/testing/selftests/bpf/config
+++ b/tools/testing/selftests/bpf/config
@@ -62,3 +62,5 @@ CONFIG_TEST_BPF=m
 CONFIG_USERFAULTFD=y
 CONFIG_VXLAN=y
 CONFIG_XDP_SOCKETS=y
+CONFIG_MODULE_SIG=y
+CONFIG_KEYS=y
diff --git a/tools/testing/selftests/bpf/prog_tests/verify_pkcs7_sig.c b/tools/testing/selftests/bpf/prog_tests/verify_pkcs7_sig.c
new file mode 100644
index 000000000000..20be68d4cce4
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/verify_pkcs7_sig.c
@@ -0,0 +1,399 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <endian.h>
+#include <limits.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <sys/mman.h>
+#include <linux/keyctl.h>
+#include <test_progs.h>
+
+#include "test_verify_pkcs7_sig.skel.h"
+
+#define MAX_DATA_SIZE (1024 * 1024)
+#define MAX_SIG_SIZE 1024
+
+#define VERIFY_USE_SECONDARY_KEYRING (1UL)
+#define VERIFY_USE_PLATFORM_KEYRING  (2UL)
+
+/* In stripped ARM and x86-64 modules, ~ is surprisingly rare. */
+#define MODULE_SIG_STRING "~Module signature appended~\n"
+
+/*
+ * Module signature information block.
+ *
+ * The constituents of the signature section are, in order:
+ *
+ *	- Signer's name
+ *	- Key identifier
+ *	- Signature data
+ *	- Information block
+ */
+struct module_signature {
+	u8	algo;		/* Public-key crypto algorithm [0] */
+	u8	hash;		/* Digest algorithm [0] */
+	u8	id_type;	/* Key identifier type [PKEY_ID_PKCS7] */
+	u8	signer_len;	/* Length of signer's name [0] */
+	u8	key_id_len;	/* Length of key identifier [0] */
+	u8	__pad[3];
+	__be32	sig_len;	/* Length of signature data */
+};
+
+struct data {
+	u8 data[MAX_DATA_SIZE];
+	u32 data_len;
+	u8 sig[MAX_SIG_SIZE];
+	u32 sig_len;
+};
+
+static bool kfunc_not_supported;
+
+static int libbpf_print_cb(enum libbpf_print_level level, const char *fmt,
+			   va_list args)
+{
+	if (strcmp(fmt, "libbpf: extern (func ksym) '%s': not found in kernel or module BTFs\n"))
+		return 0;
+
+	if (strcmp(va_arg(args, char *), "bpf_verify_pkcs7_signature"))
+		return 0;
+
+	kfunc_not_supported = true;
+	return 0;
+}
+
+static int _run_setup_process(const char *setup_dir, const char *cmd)
+{
+	int child_pid, child_status;
+
+	child_pid = fork();
+	if (child_pid == 0) {
+		execlp("./verify_sig_setup.sh", "./verify_sig_setup.sh", cmd,
+		       setup_dir, NULL);
+		exit(errno);
+
+	} else if (child_pid > 0) {
+		waitpid(child_pid, &child_status, 0);
+		return WEXITSTATUS(child_status);
+	}
+
+	return -EINVAL;
+}
+
+static int populate_data_item_str(const char *tmp_dir, struct data *data_item)
+{
+	struct stat st;
+	char data_template[] = "/tmp/dataXXXXXX";
+	char path[PATH_MAX];
+	int ret, fd, child_status, child_pid;
+
+	data_item->data_len = 4;
+	memcpy(data_item->data, "test", data_item->data_len);
+
+	fd = mkstemp(data_template);
+	if (fd == -1)
+		return -errno;
+
+	ret = write(fd, data_item->data, data_item->data_len);
+
+	close(fd);
+
+	if (ret != data_item->data_len) {
+		ret = -EIO;
+		goto out;
+	}
+
+	child_pid = fork();
+
+	if (child_pid == -1) {
+		ret = -errno;
+		goto out;
+	}
+
+	if (child_pid == 0) {
+		snprintf(path, sizeof(path), "%s/signing_key.pem", tmp_dir);
+
+		return execlp("./sign-file", "./sign-file", "-d", "sha256",
+			      path, path, data_template, NULL);
+	}
+
+	waitpid(child_pid, &child_status, 0);
+
+	ret = WEXITSTATUS(child_status);
+	if (ret)
+		goto out;
+
+	snprintf(path, sizeof(path), "%s.p7s", data_template);
+
+	ret = stat(path, &st);
+	if (ret == -1) {
+		ret = -errno;
+		goto out;
+	}
+
+	if (st.st_size > sizeof(data_item->sig)) {
+		ret = -EINVAL;
+		goto out_sig;
+	}
+
+	data_item->sig_len = st.st_size;
+
+	fd = open(path, O_RDONLY);
+	if (fd == -1) {
+		ret = -errno;
+		goto out_sig;
+	}
+
+	ret = read(fd, data_item->sig, data_item->sig_len);
+
+	close(fd);
+
+	if (ret != data_item->sig_len) {
+		ret = -EIO;
+		goto out_sig;
+	}
+
+	ret = 0;
+out_sig:
+	unlink(path);
+out:
+	unlink(data_template);
+	return ret;
+}
+
+static int populate_data_item_mod(struct data *data_item)
+{
+	char mod_path[PATH_MAX], *mod_path_ptr;
+	struct stat st;
+	void *mod;
+	FILE *fp;
+	struct module_signature ms;
+	int ret, fd, modlen, marker_len, sig_len;
+
+	data_item->data_len = 0;
+
+	if (stat("/lib/modules", &st) == -1)
+		return 0;
+
+	/* Requires CONFIG_TCP_CONG_BIC=m. */
+	fp = popen("find /lib/modules/$(uname -r) -name tcp_bic.ko", "r");
+	if (!fp)
+		return 0;
+
+	mod_path_ptr = fgets(mod_path, sizeof(mod_path), fp);
+	pclose(fp);
+
+	if (!mod_path_ptr)
+		return 0;
+
+	mod_path_ptr = strchr(mod_path, '\n');
+	if (!mod_path_ptr)
+		return 0;
+
+	*mod_path_ptr = '\0';
+
+	if (stat(mod_path, &st) == -1)
+		return 0;
+
+	modlen = st.st_size;
+	marker_len = sizeof(MODULE_SIG_STRING) - 1;
+
+	fd = open(mod_path, O_RDONLY);
+	if (fd == -1)
+		return -errno;
+
+	mod = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+
+	close(fd);
+
+	if (mod == MAP_FAILED)
+		return -errno;
+
+	if (strncmp(mod + modlen - marker_len, MODULE_SIG_STRING, marker_len)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	modlen -= marker_len;
+
+	memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
+
+	sig_len = __be32_to_cpu(ms.sig_len);
+	modlen -= sig_len + sizeof(ms);
+
+	if (modlen > sizeof(data_item->data)) {
+		ret = -E2BIG;
+		goto out;
+	}
+
+	memcpy(data_item->data, mod, modlen);
+	data_item->data_len = modlen;
+
+	if (sig_len > sizeof(data_item->sig)) {
+		ret = -E2BIG;
+		goto out;
+	}
+
+	memcpy(data_item->sig, mod + modlen, sig_len);
+	data_item->sig_len = sig_len;
+	ret = 0;
+out:
+	munmap(mod, st.st_size);
+	return ret;
+}
+
+void test_verify_pkcs7_sig(void)
+{
+	libbpf_print_fn_t old_print_cb;
+	char tmp_dir_template[] = "/tmp/verify_sigXXXXXX";
+	char *tmp_dir;
+	struct test_verify_pkcs7_sig *skel = NULL;
+	struct bpf_map *map;
+	struct data data;
+	int ret, zero = 0;
+
+	/* Trigger creation of session keyring. */
+	syscall(__NR_request_key, "keyring", "_uid.0", NULL,
+		KEY_SPEC_SESSION_KEYRING);
+
+	tmp_dir = mkdtemp(tmp_dir_template);
+	if (!ASSERT_OK_PTR(tmp_dir, "mkdtemp"))
+		return;
+
+	ret = _run_setup_process(tmp_dir, "setup");
+	if (!ASSERT_OK(ret, "_run_setup_process"))
+		goto close_prog;
+
+	skel = test_verify_pkcs7_sig__open();
+	if (!ASSERT_OK_PTR(skel, "test_verify_pkcs7_sig__open"))
+		goto close_prog;
+
+	old_print_cb = libbpf_set_print(libbpf_print_cb);
+	ret = test_verify_pkcs7_sig__load(skel);
+	libbpf_set_print(old_print_cb);
+
+	if (ret < 0 && kfunc_not_supported) {
+		printf(
+		  "%s:SKIP:bpf_verify_pkcs7_signature() kfunc not supported\n",
+		  __func__);
+		test__skip();
+		goto close_prog;
+	}
+
+	if (!ASSERT_OK(ret, "test_verify_pkcs7_sig__load"))
+		goto close_prog;
+
+	ret = test_verify_pkcs7_sig__attach(skel);
+	if (!ASSERT_OK(ret, "test_verify_pkcs7_sig__attach"))
+		goto close_prog;
+
+	map = bpf_object__find_map_by_name(skel->obj, "data_input");
+	if (!ASSERT_OK_PTR(map, "data_input not found"))
+		goto close_prog;
+
+	skel->bss->monitored_pid = getpid();
+
+	/* Test without data and signature. */
+	skel->bss->user_keyring_serial = KEY_SPEC_SESSION_KEYRING;
+
+	ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data, BPF_ANY);
+	if (!ASSERT_LT(ret, 0, "bpf_map_update_elem data_input"))
+		goto close_prog;
+
+	/* Test successful signature verification with session keyring. */
+	ret = populate_data_item_str(tmp_dir, &data);
+	if (!ASSERT_OK(ret, "populate_data_item_str"))
+		goto close_prog;
+
+	ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data, BPF_ANY);
+	if (!ASSERT_OK(ret, "bpf_map_update_elem data_input"))
+		goto close_prog;
+
+	/* Test successful signature verification with testing keyring. */
+	skel->bss->user_keyring_serial = syscall(__NR_request_key, "keyring",
+						 "ebpf_testing_keyring", NULL,
+						 KEY_SPEC_SESSION_KEYRING);
+
+	ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data, BPF_ANY);
+	if (!ASSERT_OK(ret, "bpf_map_update_elem data_input"))
+		goto close_prog;
+
+	/*
+	 * Ensure key_task_permission() is called and rejects the keyring
+	 * (no Search permission).
+	 */
+	syscall(__NR_keyctl, KEYCTL_SETPERM, skel->bss->user_keyring_serial,
+		0x37373737);
+
+	ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data, BPF_ANY);
+	if (!ASSERT_LT(ret, 0, "bpf_map_update_elem data_input"))
+		goto close_prog;
+
+	syscall(__NR_keyctl, KEYCTL_SETPERM, skel->bss->user_keyring_serial,
+		0x3f3f3f3f);
+
+	/*
+	 * Ensure key_validate() is called and rejects the keyring (key expired)
+	 */
+	syscall(__NR_keyctl, KEYCTL_SET_TIMEOUT,
+		skel->bss->user_keyring_serial, 1);
+	sleep(1);
+
+	ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data, BPF_ANY);
+	if (!ASSERT_LT(ret, 0, "bpf_map_update_elem data_input"))
+		goto close_prog;
+
+	skel->bss->user_keyring_serial = KEY_SPEC_SESSION_KEYRING;
+
+	/* Test with corrupted data (signature verification should fail). */
+	data.data[0] = 'a';
+	ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data, BPF_ANY);
+	if (!ASSERT_LT(ret, 0, "bpf_map_update_elem data_input"))
+		goto close_prog;
+
+	ret = populate_data_item_mod(&data);
+	if (!ASSERT_OK(ret, "populate_data_item_mod"))
+		goto close_prog;
+
+	/* Test signature verification with system keyrings. */
+	if (data.data_len) {
+		skel->bss->user_keyring_serial = 0;
+		skel->bss->system_keyring_id = 0;
+
+		ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data,
+					  BPF_ANY);
+		if (!ASSERT_OK(ret, "bpf_map_update_elem data_input"))
+			goto close_prog;
+
+		skel->bss->system_keyring_id = VERIFY_USE_SECONDARY_KEYRING;
+
+		ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data,
+					  BPF_ANY);
+		if (!ASSERT_OK(ret, "bpf_map_update_elem data_input"))
+			goto close_prog;
+
+		skel->bss->system_keyring_id = VERIFY_USE_PLATFORM_KEYRING;
+
+		ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data,
+					  BPF_ANY);
+		ASSERT_LT(ret, 0, "bpf_map_update_elem data_input");
+	}
+
+close_prog:
+	_run_setup_process(tmp_dir, "cleanup");
+
+	if (!skel)
+		return;
+
+	skel->bss->monitored_pid = 0;
+	test_verify_pkcs7_sig__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_verify_pkcs7_sig.c b/tools/testing/selftests/bpf/progs/test_verify_pkcs7_sig.c
new file mode 100644
index 000000000000..4ceab545d99a
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_verify_pkcs7_sig.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ */
+
+#include "vmlinux.h"
+#include <errno.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#define MAX_DATA_SIZE (1024 * 1024)
+#define MAX_SIG_SIZE 1024
+
+typedef __u8 u8;
+typedef __u16 u16;
+typedef __u32 u32;
+typedef __u64 u64;
+
+struct bpf_dynptr {
+	__u64 :64;
+	__u64 :64;
+} __attribute__((aligned(8)));
+
+extern struct bpf_key *bpf_lookup_user_key(__u32 serial, __u64 flags) __ksym;
+extern struct bpf_key *bpf_lookup_system_key(__u64 id) __ksym;
+extern void bpf_key_put(struct bpf_key *key) __ksym;
+extern int bpf_verify_pkcs7_signature(struct bpf_dynptr *data_ptr,
+				      struct bpf_dynptr *sig_ptr,
+				      struct bpf_key *trusted_keyring) __ksym;
+
+u32 monitored_pid;
+u32 user_keyring_serial;
+u64 system_keyring_id;
+
+struct data {
+	u8 data[MAX_DATA_SIZE];
+	u32 data_len;
+	u8 sig[MAX_SIG_SIZE];
+	u32 sig_len;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, struct data);
+} data_input SEC(".maps");
+
+char _license[] SEC("license") = "GPL";
+
+SEC("lsm.s/bpf")
+int BPF_PROG(bpf, int cmd, union bpf_attr *attr, unsigned int size)
+{
+	struct bpf_dynptr data_ptr, sig_ptr;
+	struct data *data_val;
+	struct bpf_key *trusted_keyring;
+	u32 pid;
+	u64 value;
+	int ret, zero = 0;
+
+	pid = bpf_get_current_pid_tgid() >> 32;
+	if (pid != monitored_pid)
+		return 0;
+
+	data_val = bpf_map_lookup_elem(&data_input, &zero);
+	if (!data_val)
+		return 0;
+
+	bpf_probe_read(&value, sizeof(value), &attr->value);
+
+	bpf_copy_from_user(data_val, sizeof(struct data),
+			   (void *)(unsigned long)value);
+
+	if (data_val->data_len > sizeof(data_val->data))
+		return -EINVAL;
+
+	bpf_dynptr_from_mem(data_val->data, data_val->data_len, 0, &data_ptr);
+
+	if (data_val->sig_len > sizeof(data_val->sig))
+		return -EINVAL;
+
+	bpf_dynptr_from_mem(data_val->sig, data_val->sig_len, 0, &sig_ptr);
+
+	if (user_keyring_serial)
+		trusted_keyring = bpf_lookup_user_key(user_keyring_serial, 0);
+	else
+		trusted_keyring = bpf_lookup_system_key(system_keyring_id);
+
+	if (!trusted_keyring)
+		return -ENOENT;
+
+	ret = bpf_verify_pkcs7_signature(&data_ptr, &sig_ptr, trusted_keyring);
+
+	bpf_key_put(trusted_keyring);
+
+	return ret;
+}
diff --git a/tools/testing/selftests/bpf/verify_sig_setup.sh b/tools/testing/selftests/bpf/verify_sig_setup.sh
new file mode 100755
index 000000000000..ba08922b4a27
--- /dev/null
+++ b/tools/testing/selftests/bpf/verify_sig_setup.sh
@@ -0,0 +1,104 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+set -e
+set -u
+set -o pipefail
+
+VERBOSE="${SELFTESTS_VERBOSE:=0}"
+LOG_FILE="$(mktemp /tmp/verify_sig_setup.log.XXXXXX)"
+
+x509_genkey_content="\
+[ req ]
+default_bits = 2048
+distinguished_name = req_distinguished_name
+prompt = no
+string_mask = utf8only
+x509_extensions = myexts
+
+[ req_distinguished_name ]
+CN = eBPF Signature Verification Testing Key
+
+[ myexts ]
+basicConstraints=critical,CA:FALSE
+keyUsage=digitalSignature
+subjectKeyIdentifier=hash
+authorityKeyIdentifier=keyid
+"
+
+usage()
+{
+	echo "Usage: $0 <setup|cleanup <existing_tmp_dir>"
+	exit 1
+}
+
+setup()
+{
+	local tmp_dir="$1"
+
+	echo "${x509_genkey_content}" > ${tmp_dir}/x509.genkey
+
+	openssl req -new -nodes -utf8 -sha256 -days 36500 \
+			-batch -x509 -config ${tmp_dir}/x509.genkey \
+			-outform PEM -out ${tmp_dir}/signing_key.pem \
+			-keyout ${tmp_dir}/signing_key.pem 2>&1
+
+	openssl x509 -in ${tmp_dir}/signing_key.pem -out \
+		${tmp_dir}/signing_key.der -outform der
+
+	key_id=$(cat ${tmp_dir}/signing_key.der | keyctl padd asymmetric ebpf_testing_key @s)
+
+	keyring_id=$(keyctl newring ebpf_testing_keyring @s)
+	keyctl link $key_id $keyring_id
+}
+
+cleanup() {
+	local tmp_dir="$1"
+
+	keyctl unlink $(keyctl search @s asymmetric ebpf_testing_key) @s
+	keyctl unlink $(keyctl search @s keyring ebpf_testing_keyring) @s
+	rm -rf ${tmp_dir}
+}
+
+catch()
+{
+	local exit_code="$1"
+	local log_file="$2"
+
+	if [[ "${exit_code}" -ne 0 ]]; then
+		cat "${log_file}" >&3
+	fi
+
+	rm -f "${log_file}"
+	exit ${exit_code}
+}
+
+main()
+{
+	[[ $# -ne 2 ]] && usage
+
+	local action="$1"
+	local tmp_dir="$2"
+
+	[[ ! -d "${tmp_dir}" ]] && echo "Directory ${tmp_dir} doesn't exist" && exit 1
+
+	if [[ "${action}" == "setup" ]]; then
+		setup "${tmp_dir}"
+	elif [[ "${action}" == "cleanup" ]]; then
+		cleanup "${tmp_dir}"
+	else
+		echo "Unknown action: ${action}"
+		exit 1
+	fi
+}
+
+trap 'catch "$?" "${LOG_FILE}"' EXIT
+
+if [[ "${VERBOSE}" -eq 0 ]]; then
+	# Save the stderr to 3 so that we can output back to
+	# it incase of an error.
+	exec 3>&2 1>"${LOG_FILE}" 2>&1
+fi
+
+main "$@"
+rm -f "${LOG_FILE}"
-- 
2.25.1

Re: [PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Alexei Starovoitov]

On Wed, Aug 10, 2022 at 06:59:28PM +0200, Roberto Sassu wrote:
> +
> +static int __init bpf_key_sig_kfuncs_init(void)
> +{
> +	int ret;
> +
> +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> +					&bpf_key_sig_kfunc_set);
> +	if (!ret)
> +		return 0;
> +
> +	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
> +					 &bpf_key_sig_kfunc_set);

Isn't this a watery water ?
Don't you have a patch 1 ?
What am I missing ?

RE: [PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Roberto Sassu]

> From: Alexei Starovoitov [mailto:alexei.starovoitov@gmail.com]
> Sent: Wednesday, August 10, 2022 11:34 PM
> On Wed, Aug 10, 2022 at 06:59:28PM +0200, Roberto Sassu wrote:
> > +
> > +static int __init bpf_key_sig_kfuncs_init(void)
> > +{
> > +	int ret;
> > +
> > +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> > +					&bpf_key_sig_kfunc_set);
> > +	if (!ret)
> > +		return 0;
> > +
> > +	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
> > +					 &bpf_key_sig_kfunc_set);
> 
> Isn't this a watery water ?
> Don't you have a patch 1 ?
> What am I missing ?

Uhm, yes. I had doubts too. That was what also KP did.

It makes sense to register once, since we mapped LSM to
TRACING.

Will resend only this patch. And I will figure out why CI failed.

Roberto

RE: [PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Roberto Sassu]

> From: Roberto Sassu [mailto:roberto.sassu@huawei.com]
> Sent: Thursday, August 11, 2022 9:47 AM
> > From: Alexei Starovoitov [mailto:alexei.starovoitov@gmail.com]
> > Sent: Wednesday, August 10, 2022 11:34 PM
> > On Wed, Aug 10, 2022 at 06:59:28PM +0200, Roberto Sassu wrote:
> > > +
> > > +static int __init bpf_key_sig_kfuncs_init(void)
> > > +{
> > > +	int ret;
> > > +
> > > +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> > > +					&bpf_key_sig_kfunc_set);
> > > +	if (!ret)
> > > +		return 0;
> > > +
> > > +	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
> > > +					 &bpf_key_sig_kfunc_set);
> >
> > Isn't this a watery water ?
> > Don't you have a patch 1 ?
> > What am I missing ?
> 
> Uhm, yes. I had doubts too. That was what also KP did.
> 
> It makes sense to register once, since we mapped LSM to
> TRACING.
> 
> Will resend only this patch. And I will figure out why CI failed.

Adding in CC Daniel Müller, which worked on this.

I think the issue is that some kernel options are set to =m.
This causes the CI to miss all kernel modules, since they are
not copied to the virtual machine that executes the tests.

I'm testing this patch:

https://github.com/robertosassu/libbpf-ci/commit/b665e001b58c4ddb792a2a68098ea5dc6936b15c

Roberto

Re: [PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Daniel Müller]

On Thu, Aug 11, 2022 at 12:02:57PM +0000, Roberto Sassu wrote:
> > From: Roberto Sassu [mailto:roberto.sassu@huawei.com]
> > Sent: Thursday, August 11, 2022 9:47 AM
> > > From: Alexei Starovoitov [mailto:alexei.starovoitov@gmail.com]
> > > Sent: Wednesday, August 10, 2022 11:34 PM
> > > On Wed, Aug 10, 2022 at 06:59:28PM +0200, Roberto Sassu wrote:
> > > > +
> > > > +static int __init bpf_key_sig_kfuncs_init(void)
> > > > +{
> > > > +	int ret;
> > > > +
> > > > +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> > > > +					&bpf_key_sig_kfunc_set);
> > > > +	if (!ret)
> > > > +		return 0;
> > > > +
> > > > +	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
> > > > +					 &bpf_key_sig_kfunc_set);
> > >
> > > Isn't this a watery water ?
> > > Don't you have a patch 1 ?
> > > What am I missing ?
> > 
> > Uhm, yes. I had doubts too. That was what also KP did.
> > 
> > It makes sense to register once, since we mapped LSM to
> > TRACING.
> > 
> > Will resend only this patch. And I will figure out why CI failed.
> 
> Adding in CC Daniel Müller, which worked on this.
> 
> I think the issue is that some kernel options are set to =m.
> This causes the CI to miss all kernel modules, since they are
> not copied to the virtual machine that executes the tests.
> 
> I'm testing this patch:
> 
> https://github.com/robertosassu/libbpf-ci/commit/b665e001b58c4ddb792a2a68098ea5dc6936b15c

I commented on the pull request. Would it make sense to adjust the
kernel configuration in this repository instead? I am worried that
otherwise everybody may need a similar work around, depending on how
selftests are ultimately run.

Thanks,
Daniel

Re: [PATCH v10 4/9] KEYS: Move KEY_LOOKUP_ to include/linux/key.h

[KP Singh]

On Wed, Aug 10, 2022 at 6:59 PM Roberto Sassu <roberto.sassu@huawei.com> wrote:
>
> In preparation for the patch that introduces the bpf_lookup_user_key() eBPF
> kfunc, move KEY_LOOKUP_ definitions to include/linux/key.h, to be able to
> validate the kfunc parameters.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Reviewed-by: KP Singh <kpsingh@kernel.org>

Re: [PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[KP Singh]

On Wed, Aug 10, 2022 at 7:01 PM Roberto Sassu <roberto.sassu@huawei.com> wrote:
>
> Add the bpf_lookup_user_key(), bpf_lookup_system_key() and bpf_key_put()
> kfuncs, to respectively search a key with a given serial and flags, obtain

nit: "with a given key handle serial number"

> a key from a pre-determined ID defined in include/linux/verification.h, and
> cleanup.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
>  include/linux/bpf.h      |   6 ++
>  kernel/trace/bpf_trace.c | 146 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 152 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index a82f8c559ae2..d415e5e97551 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2573,4 +2573,10 @@ static inline void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype) {}
>  static inline void bpf_cgroup_atype_put(int cgroup_atype) {}
>  #endif /* CONFIG_BPF_LSM */
>
> +#ifdef CONFIG_KEYS
> +struct bpf_key {
> +       struct key *key;
> +       bool has_ref;
> +};
> +#endif /* CONFIG_KEYS */
>  #endif /* _LINUX_BPF_H */
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 68e5cdd24cef..a607bb0be738 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -20,6 +20,8 @@
>  #include <linux/fprobe.h>
>  #include <linux/bsearch.h>
>  #include <linux/sort.h>
> +#include <linux/key.h>
> +#include <linux/verification.h>
>
>  #include <net/bpf_sk_storage.h>
>
> @@ -1181,6 +1183,150 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = {
>         .arg1_type      = ARG_PTR_TO_CTX,
>  };
>
> +#ifdef CONFIG_KEYS
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> +                 "kfuncs which will be used in BPF programs");
> +
> +/**
> + * bpf_lookup_user_key - lookup a key by its serial
> + * @serial: key serial

nit: "key handle serial number"


> + * @flags: lookup-specific flags
> + *
> + * Search a key with a given *serial* and the provided *flags*. The
> + * returned key, if found, has the reference count incremented by
> + * one, and is stored in a bpf_key structure, returned to the caller.

nit: This can be made a little clearer with:

Search a key with a given *serial* and the provided *flags*.
If found, increment the reference count of the key by
one, and return it in the bpf_key structure.


> + * The bpf_key structure must be passed to bpf_key_put() when done
> + * with it, so that the key reference count is decremented and the
> + * bpf_key structure is freed.
> + *
> + * Permission checks are deferred to the time the key is used by
> + * one of the available key-specific kfuncs.
> + *
> + * Set *flags* with 1, to attempt creating a requested special
> + * keyring (e.g. session keyring), if it doesn't yet exist. Set
> + * *flags* with 2 to lookup a key without waiting for the key
> + * construction, and to retrieve uninstantiated keys (keys without
> + * data attached to them).

The 1 and 2 here are so confusing why not just use their actual names here:
KEY_LOOKUP_CREATE and KEY_LOOKUP_PARTIAL.

> + *
> + * Return: a bpf_key pointer with a valid key pointer if the key is found, a
> + *         NULL pointer otherwise.
> + */
> +struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags)
> +{
> +       key_ref_t key_ref;
> +       struct bpf_key *bkey;
> +
> +       /* Keep in sync with include/linux/key.h. */

What does this comment mean? Does this mean that more flags may end up in this
check? if so, let's just put an inline function in include/linux/key.h?

> +       if (flags & ~(KEY_LOOKUP_CREATE | KEY_LOOKUP_PARTIAL))
> +               return NULL;
> +
> +       /*
> +        * Permission check is deferred until actual kfunc using the key,
> +        * since here the intent of the caller is not yet known.
> +        *
> +        * We cannot trust the caller to provide the needed permission as
> +        * argument, since nothing prevents the caller from using the
> +        * obtained key for a different purpose than the one declared.
> +        */

nit: This can just be a simple comment.

Permission check is deferred until the key is used as the intent of the
caller is unknown here.

> +       key_ref = lookup_user_key(serial, flags, KEY_DEFER_PERM_CHECK);
> +       if (IS_ERR(key_ref))
> +               return NULL;
> +
> +       bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC);
> +       if (!bkey) {
> +               key_put(key_ref_to_ptr(key_ref));
> +               return NULL;
> +       }
> +
> +       bkey->key = key_ref_to_ptr(key_ref);
> +       bkey->has_ref = true;
> +
> +       return bkey;
> +}
> +
> +/**
> + * bpf_lookup_system_key - lookup a key by a system-defined ID
> + * @id: key ID
> + *
> + * Obtain a bpf_key structure with a key pointer set to the passed key ID.
> + * The key pointer is marked as invalid, to prevent bpf_key_put() from
> + * attempting to decrement the key reference count on that pointer. The key
> + * pointer set in such way is currently understood only by
> + * verify_pkcs7_signature().
> + *
> + * Set *id* to one of the values defined in include/linux/verification.h:
> + * 0 for the primary keyring (immutable keyring of system keys); 1 for both

Please use VERIFY_USE_PLATFORM_KEYRING
and VERIFY_USE_SECONDARY_KEYRING here instead of 0 and 1


> + * the primary and secondary keyring (where keys can be added only if they
> + * are vouched for by existing keys in those keyrings); 2 for the platform
> + * keyring (primarily used by the integrity subsystem to verify a kexec'ed
> + * kerned image and, possibly, the initramfs signature).
> + *
> + * Return: a bpf_key pointer with an invalid key pointer set from the
> + *         pre-determined ID on success, a NULL pointer otherwise
> + */
> +struct bpf_key *bpf_lookup_system_key(u64 id)
> +{
> +       struct bpf_key *bkey;
> +
> +       /* Keep in sync with defs in include/linux/verification.h. */

Here too, it's best to introduce a "MAX" value or a small inline helper
rather than this comment.

> +       if (id > (unsigned long)VERIFY_USE_PLATFORM_KEYRING)
> +               return NULL;
> +
> +       bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC);
> +       if (!bkey)
> +               return NULL;
> +
> +       bkey->key = (struct key *)(unsigned long)id;
> +       bkey->has_ref = false;
> +
> +       return bkey;
> +}
> +
> +/**
> + * bpf_key_put - decrement key reference count if key is valid and free bpf_key
> + * @bkey: bpf_key structure
> + *
> + * Decrement the reference count of the key inside *bkey*, if the pointer
> + * is valid, and free *bkey*.
> + */

This is more of a style thing but your comment literally describes the
small function
below. Do we really need this?

> +void bpf_key_put(struct bpf_key *bkey)
> +{
> +       if (bkey->has_ref)
> +               key_put(bkey->key);
> +
> +       kfree(bkey);
> +}
> +
> +__diag_pop();
> +
> +BTF_SET8_START(key_sig_kfunc_set)
> +BTF_ID_FLAGS(func, bpf_lookup_user_key, KF_ACQUIRE | KF_RET_NULL | KF_SLEEPABLE)
> +BTF_ID_FLAGS(func, bpf_lookup_system_key, KF_ACQUIRE | KF_RET_NULL)
> +BTF_ID_FLAGS(func, bpf_key_put, KF_RELEASE)
> +BTF_SET8_END(key_sig_kfunc_set)
> +
> +static const struct btf_kfunc_id_set bpf_key_sig_kfunc_set = {
> +       .owner = THIS_MODULE,
> +       .set = &key_sig_kfunc_set,
> +};
> +
> +static int __init bpf_key_sig_kfuncs_init(void)
> +{
> +       int ret;
> +
> +       ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> +                                       &bpf_key_sig_kfunc_set);
> +       if (!ret)
> +               return 0;
> +
> +       return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
> +                                        &bpf_key_sig_kfunc_set);
> +}
> +
> +late_initcall(bpf_key_sig_kfuncs_init);
> +#endif /* CONFIG_KEYS */
> +
>  static const struct bpf_func_proto *
>  bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  {
> --
> 2.25.1
>

[...]

Re: [PATCH v10 6/9] bpf: Add bpf_verify_pkcs7_signature() kfunc

[KP Singh]

On Wed, Aug 10, 2022 at 7:01 PM Roberto Sassu <roberto.sassu@huawei.com> wrote:
>
> Add the bpf_verify_pkcs7_signature() kfunc, to give eBPF security modules
> the ability to check the validity of a signature against supplied data, by
> using user-provided or system-provided keys as trust anchor.
>
> The new kfunc makes it possible to enforce mandatory policies, as eBPF
> programs might be allowed to make security decisions only based on data
> sources the system administrator approves.
>
> The caller should provide the data to be verified and the signature as eBPF
> dynamic pointers (to minimize the number of parameters) and a bpf_key
> structure containing a reference to the keyring with keys trusted for
> signature verification, obtained from bpf_lookup_user_key() or
> bpf_lookup_system_key().
>
> For bpf_key structures obtained from the former lookup function,
> bpf_verify_pkcs7_signature() completes the permission check deferred by
> that function by calling key_validate(). key_task_permission() is already
> called by the PKCS#7 code.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Acked-by: KP Singh <kpsingh@kernel.org>

RE: [PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Roberto Sassu]

> From: Daniel Müller [mailto:deso@posteo.net]
> Sent: Friday, August 12, 2022 1:52 AM
> On Thu, Aug 11, 2022 at 12:02:57PM +0000, Roberto Sassu wrote:
> > > From: Roberto Sassu [mailto:roberto.sassu@huawei.com]
> > > Sent: Thursday, August 11, 2022 9:47 AM
> > > > From: Alexei Starovoitov [mailto:alexei.starovoitov@gmail.com]
> > > > Sent: Wednesday, August 10, 2022 11:34 PM
> > > > On Wed, Aug 10, 2022 at 06:59:28PM +0200, Roberto Sassu wrote:
> > > > > +
> > > > > +static int __init bpf_key_sig_kfuncs_init(void)
> > > > > +{
> > > > > +	int ret;
> > > > > +
> > > > > +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> > > > > +					&bpf_key_sig_kfunc_set);
> > > > > +	if (!ret)
> > > > > +		return 0;
> > > > > +
> > > > > +	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
> > > > > +					 &bpf_key_sig_kfunc_set);
> > > >
> > > > Isn't this a watery water ?
> > > > Don't you have a patch 1 ?
> > > > What am I missing ?
> > >
> > > Uhm, yes. I had doubts too. That was what also KP did.
> > >
> > > It makes sense to register once, since we mapped LSM to
> > > TRACING.
> > >
> > > Will resend only this patch. And I will figure out why CI failed.
> >
> > Adding in CC Daniel Müller, which worked on this.
> >
> > I think the issue is that some kernel options are set to =m.
> > This causes the CI to miss all kernel modules, since they are
> > not copied to the virtual machine that executes the tests.
> >
> > I'm testing this patch:
> >
> > https://github.com/robertosassu/libbpf-
> ci/commit/b665e001b58c4ddb792a2a68098ea5dc6936b15c
> 
> I commented on the pull request. Would it make sense to adjust the
> kernel configuration in this repository instead? I am worried that
> otherwise everybody may need a similar work around, depending on how
> selftests are ultimately run.

The issue seems specific of the eBPF CI. Others might be able to use
kernel modules.

Either choice is fine for me.

Roberto

Re: [PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Daniel Müller]

On Fri, Aug 12, 2022 at 08:11:00AM +0000, Roberto Sassu wrote:
> > From: Daniel Müller [mailto:deso@posteo.net]
> > Sent: Friday, August 12, 2022 1:52 AM
> > On Thu, Aug 11, 2022 at 12:02:57PM +0000, Roberto Sassu wrote:
> > > > From: Roberto Sassu [mailto:roberto.sassu@huawei.com]
> > > > Sent: Thursday, August 11, 2022 9:47 AM
> > > > > From: Alexei Starovoitov [mailto:alexei.starovoitov@gmail.com]
> > > > > Sent: Wednesday, August 10, 2022 11:34 PM
> > > > > On Wed, Aug 10, 2022 at 06:59:28PM +0200, Roberto Sassu wrote:
> > > > > > +
> > > > > > +static int __init bpf_key_sig_kfuncs_init(void)
> > > > > > +{
> > > > > > +	int ret;
> > > > > > +
> > > > > > +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> > > > > > +					&bpf_key_sig_kfunc_set);
> > > > > > +	if (!ret)
> > > > > > +		return 0;
> > > > > > +
> > > > > > +	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
> > > > > > +					 &bpf_key_sig_kfunc_set);
> > > > >
> > > > > Isn't this a watery water ?
> > > > > Don't you have a patch 1 ?
> > > > > What am I missing ?
> > > >
> > > > Uhm, yes. I had doubts too. That was what also KP did.
> > > >
> > > > It makes sense to register once, since we mapped LSM to
> > > > TRACING.
> > > >
> > > > Will resend only this patch. And I will figure out why CI failed.
> > >
> > > Adding in CC Daniel Müller, which worked on this.
> > >
> > > I think the issue is that some kernel options are set to =m.
> > > This causes the CI to miss all kernel modules, since they are
> > > not copied to the virtual machine that executes the tests.
> > >
> > > I'm testing this patch:
> > >
> > > https://github.com/robertosassu/libbpf-
> > ci/commit/b665e001b58c4ddb792a2a68098ea5dc6936b15c
> > 
> > I commented on the pull request. Would it make sense to adjust the
> > kernel configuration in this repository instead? I am worried that
> > otherwise everybody may need a similar work around, depending on how
> > selftests are ultimately run.
> 
> The issue seems specific of the eBPF CI. Others might be able to use
> kernel modules.
> 
> Either choice is fine for me.

I understand that depending on how tests are run, kernel modules may be
available to be loaded. My point is that I am not aware of anything that we
would loose by having the functionality built-in to begin with (others can
correct me). So it seems as if that's an easy way to sidestep any issues of that
sort from the start and, hence, would be my preference.

Thanks,
Daniel

RE: [PATCH v10 5/9] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Roberto Sassu]

> From: KP Singh [mailto:kpsingh@kernel.org]
> Sent: Friday, August 12, 2022 2:50 AM

[...]

> > +/**
> > + * bpf_key_put - decrement key reference count if key is valid and free
> bpf_key
> > + * @bkey: bpf_key structure
> > + *
> > + * Decrement the reference count of the key inside *bkey*, if the pointer
> > + * is valid, and free *bkey*.
> > + */
> 
> This is more of a style thing but your comment literally describes the
> small function
> below. Do we really need this?

Thanks for the review, KP. Just kept this, to follow the style of kernel
documentation for functions.

Roberto