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From:   Roberto Sassu <roberto.sassu@huaweicloud.com>
To:     ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        martin.lau@linux.dev, song@kernel.org, yhs@fb.com,
        john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
        haoluo@google.com, jolsa@kernel.org, mykolal@fb.com,
        dhowells@redhat.com, jarkko@kernel.org, rostedt@goodmis.org,
        mingo@redhat.com, paul@paul-moore.com, jmorris@namei.org,
        serge@hallyn.com, shuah@kernel.org
Cc:     bpf@vger.kernel.org, keyrings@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
        deso@posteo.net, memxor@gmail.com,
        Roberto Sassu <roberto.sassu@huawei.com>
Subject: [PATCH v17 11/12] selftests/bpf: Add test for bpf_verify_pkcs7_signature() kfunc
Date:   Fri,  9 Sep 2022 14:07:35 +0200
Message-Id: <20220909120736.1027040-12-roberto.sassu@huaweicloud.com>
In-Reply-To: <20220909120736.1027040-1-roberto.sassu@huaweicloud.com>
References: <20220909120736.1027040-1-roberto.sassu@huaweicloud.com>
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From: Roberto Sassu <roberto.sassu@huawei.com>

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).

The test is currently in the deny list for s390x (JIT does not support
calling kernel function).

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 tools/testing/selftests/bpf/DENYLIST.s390x    |   1 +
 tools/testing/selftests/bpf/Makefile          |  14 +-
 tools/testing/selftests/bpf/config            |   5 +
 tools/testing/selftests/bpf/config.x86_64     |   5 -
 .../bpf/prog_tests/verify_pkcs7_sig.c         | 399 ++++++++++++++++++
 .../bpf/progs/test_verify_pkcs7_sig.c         | 100 +++++
 .../testing/selftests/bpf/verify_sig_setup.sh | 104 +++++
 7 files changed, 620 insertions(+), 8 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/DENYLIST.s390x b/tools/testing/selftests/bpf/DENYLIST.s390x
index 770c376c984d..759b2bb53b53 100644
--- a/tools/testing/selftests/bpf/DENYLIST.s390x
+++ b/tools/testing/selftests/bpf/DENYLIST.s390x
@@ -72,3 +72,4 @@ cgroup_hierarchical_stats                # JIT does not support calling kernel f
 htab_update                              # failed to attach: ERROR: strerror_r(-524)=22                                (trampoline)
 tracing_struct                           # failed to auto-attach: -524                                                 (trampoline)
 lookup_key                               # JIT does not support calling kernel function                                (kfunc)
+verify_pkcs7_sig                         # JIT does not support calling kernel function                                (kfunc)
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 6cd327f1f216..15e4bfc2e22c 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
@@ -516,7 +523,8 @@ 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 add5a5a919b4..905a9be8d0a2 100644
--- a/tools/testing/selftests/bpf/config
+++ b/tools/testing/selftests/bpf/config
@@ -33,6 +33,11 @@ CONFIG_IPV6_TUNNEL=y
 CONFIG_KEYS=y
 CONFIG_LIRC=y
 CONFIG_LWTUNNEL=y
+CONFIG_MODULE_SIG=y
+CONFIG_MODULE_SRCVERSION_ALL=y
+CONFIG_MODULE_UNLOAD=y
+CONFIG_MODULES=y
+CONFIG_MODVERSIONS=y
 CONFIG_MPLS=y
 CONFIG_MPLS_IPTUNNEL=y
 CONFIG_MPLS_ROUTING=y
diff --git a/tools/testing/selftests/bpf/config.x86_64 b/tools/testing/selftests/bpf/config.x86_64
index ce70c9509204..21ce5ea4304e 100644
--- a/tools/testing/selftests/bpf/config.x86_64
+++ b/tools/testing/selftests/bpf/config.x86_64
@@ -145,11 +145,6 @@ CONFIG_MCORE2=y
 CONFIG_MEMCG=y
 CONFIG_MEMORY_FAILURE=y
 CONFIG_MINIX_SUBPARTITION=y
-CONFIG_MODULE_SIG=y
-CONFIG_MODULE_SRCVERSION_ALL=y
-CONFIG_MODULE_UNLOAD=y
-CONFIG_MODULES=y
-CONFIG_MODVERSIONS=y
 CONFIG_NAMESPACES=y
 CONFIG_NET=y
 CONFIG_NET_9P=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