[PATCH v6 5/5] selftests/bpf: Add test for bpf_verify_pkcs7_signature() helper

[Roberto Sassu]

Ensure that signature verification is performed successfully from an eBPF
program, with the new bpf_verify_pkcs7_signature() helper.

Generate a testing signature key and compile sign-file from scripts/, so
that the test is selfcontained. Also, search for the tcb_bic.ko kernel
module, parse it in user space to extract the raw PKCS#7 signature and send
it to the eBPF program for signature verification. If tcb_bic.ko is not
found, the test does not fail.

The additional verification of a kernel module is necessary to test lookup
of a keyring with a special ID (primary, secondary or platform) since, if
kernel modules are signed, the public key is also added at kernel build
time to one of those keyrings.

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
 tools/testing/selftests/bpf/Makefile          |  14 +-
 tools/testing/selftests/bpf/config            |   2 +
 .../bpf/prog_tests/verify_pkcs7_sig.c         | 359 ++++++++++++++++++
 .../bpf/progs/test_verify_pkcs7_sig.c         |  79 ++++
 .../testing/selftests/bpf/verify_sig_setup.sh | 104 +++++
 5 files changed, 555 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 4fbd88a8ed9e..cad3607e9a6f 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 \
 	xdpxceiver 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
@@ -512,7 +519,8 @@ 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 c05904d631ec..76b65acd897e 100644
--- a/tools/testing/selftests/bpf/config
+++ b/tools/testing/selftests/bpf/config
@@ -63,3 +63,5 @@ CONFIG_NETFILTER_XT_MATCH_STATE=y
 CONFIG_IP_NF_FILTER=y
 CONFIG_IP_NF_TARGET_SYNPROXY=y
 CONFIG_IP_NF_RAW=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..85552dc48333
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/verify_pkcs7_sig.c
@@ -0,0 +1,359 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
+ */
+
+#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 LOG_BUF_SIZE 16384
+
+/* 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 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)
+{
+	char tmp_dir_template[] = "/tmp/verify_sigXXXXXX";
+	char *tmp_dir;
+	char *buf = NULL;
+	struct test_verify_pkcs7_sig *skel = NULL;
+	struct bpf_map *map;
+	struct data data;
+	int ret, zero = 0;
+
+	LIBBPF_OPTS(bpf_object_open_opts, opts);
+
+	/* 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;
+
+	buf = malloc(LOG_BUF_SIZE);
+	if (!ASSERT_OK_PTR(buf, "malloc"))
+		goto close_prog;
+
+	opts.kernel_log_buf = buf;
+	opts.kernel_log_size = LOG_BUF_SIZE;
+	opts.kernel_log_level = 1;
+
+	skel = test_verify_pkcs7_sig__open_opts(&opts);
+	if (!ASSERT_OK_PTR(skel, "test_verify_pkcs7_sig__open_opts"))
+		goto close_prog;
+
+	ret = test_verify_pkcs7_sig__load(skel);
+
+	if (ret < 0 && strstr(buf, "unknown func bpf_verify_pkcs7_signature")) {
+		printf(
+		  "%s:SKIP:bpf_verify_pkcs7_signature() helper 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;
+
+	ret = populate_data_item_str(tmp_dir, &data);
+	if (!ASSERT_OK(ret, "populate_data_item_str"))
+		goto close_prog;
+
+	skel->bss->monitored_pid = getpid();
+	skel->bss->trusted_keyring_serial = 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"))
+		goto close_prog;
+
+	/* Search the verification key in the testing keyring. */
+	skel->bss->trusted_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"))
+		goto close_prog;
+
+	/* Corrupt 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;
+
+	if (data.data_len) {
+		skel->bss->trusted_keyring_serial = 0;
+		skel->bss->trusted_keyring_id = 0;
+
+		ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data,
+					  BPF_ANY);
+		if (!ASSERT_OK(ret, "bpf_map_update_elem"))
+			goto close_prog;
+
+		skel->bss->trusted_keyring_id = 1;
+
+		ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data,
+					  BPF_ANY);
+		if (!ASSERT_OK(ret, "bpf_map_update_elem"))
+			goto close_prog;
+
+		/* Verification key is not in the platform keyring. */
+		skel->bss->trusted_keyring_id = 2;
+
+		ret = bpf_map_update_elem(bpf_map__fd(map), &zero, &data,
+					  BPF_ANY);
+		ASSERT_LT(ret, 0, "bpf_map_update_elem");
+	}
+
+close_prog:
+	_run_setup_process(tmp_dir, "cleanup");
+	free(buf);
+
+	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..e9937f1ec541
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_verify_pkcs7_sig.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
+ */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <linux/bpf.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;
+
+u32 monitored_pid;
+u32 trusted_keyring_serial;
+unsigned long trusted_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;
+	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);
+
+	return bpf_verify_pkcs7_signature(&data_ptr, &sig_ptr,
+					  trusted_keyring_serial, 0,
+					  trusted_keyring_id);
+}
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