Merge branch 'bpf-lsm: Extend interoperability with IMA'

Roberto Sassu says:

====================
Extend the interoperability with IMA, to give wider flexibility for the
implementation of integrity-focused LSMs based on eBPF.

Patch 1 fixes some style issues.

Patches 2-6 give the ability to eBPF-based LSMs to take advantage of the
measurement capability of IMA without needing to setup a policy in IMA
(those LSMs might implement the policy capability themselves).

Patches 7-9 allow eBPF-based LSMs to evaluate files read by the kernel.

Changelog

v2:
- Add better description to patch 1 (suggested by Shuah)
- Recalculate digest if it is not fresh (when IMA_COLLECTED flag not set)
- Move declaration of bpf_ima_file_hash() at the end (suggested by
  Yonghong)
- Add tests to check if the digest has been recalculated
- Add deny test for bpf_kernel_read_file()
- Add description to tests

v1:
- Modify ima_file_hash() only and allow the usage of the function with the
  modified behavior by eBPF-based LSMs through the new function
  bpf_ima_file_hash() (suggested by Mimi)
- Make bpf_lsm_kernel_read_file() sleepable so that bpf_ima_inode_hash()
  and bpf_ima_file_hash() can be called inside the implementation of
  eBPF-based LSMs for this hook
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

4 files changed, 250 insertions, 11 deletions

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e9978a916c3e..99fab54ae9c0 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5119,6 +5119,16 @@ union bpf_attr {
  *		0 on success.
  *		**-EINVAL** for invalid input
  *		**-EOPNOTSUPP** for unsupported protocol
+ *
+ * long bpf_ima_file_hash(struct file *file, void *dst, u32 size)
+ *	Description
+ *		Returns a calculated IMA hash of the *file*.
+ *		If the hash is larger than *size*, then only *size*
+ *		bytes will be copied to *dst*
+ *	Return
+ *		The **hash_algo** is returned on success,
+ *		**-EOPNOTSUP** if the hash calculation failed or **-EINVAL** if
+ *		invalid arguments are passed.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5314,6 +5324,7 @@ union bpf_attr {
 	FN(xdp_store_bytes),		\
 	FN(copy_from_user_task),	\
 	FN(skb_set_tstamp),		\
+	FN(ima_file_hash),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/tools/testing/selftests/bpf/ima_setup.sh b/tools/testing/selftests/bpf/ima_setup.sh
index 8e62581113a3..8ecead4ccad0 100755
--- a/tools/testing/selftests/bpf/ima_setup.sh
+++ b/tools/testing/selftests/bpf/ima_setup.sh
@@ -12,7 +12,7 @@ LOG_FILE="$(mktemp /tmp/ima_setup.XXXX.log)"
 
 usage()
 {
-	echo "Usage: $0 <setup|cleanup|run> <existing_tmp_dir>"
+	echo "Usage: $0 <setup|cleanup|run|modify-bin|restore-bin|load-policy> <existing_tmp_dir>"
 	exit 1
 }
 
@@ -51,6 +51,7 @@ setup()
 
 	ensure_mount_securityfs
 	echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${IMA_POLICY_FILE}
+	echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${mount_dir}/policy_test
 }
 
 cleanup() {
@@ -77,6 +78,32 @@ run()
 	exec "${copied_bin_path}"
 }
 
+modify_bin()
+{
+	local tmp_dir="$1"
+	local mount_dir="${tmp_dir}/mnt"
+	local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+
+	echo "mod" >> "${copied_bin_path}"
+}
+
+restore_bin()
+{
+	local tmp_dir="$1"
+	local mount_dir="${tmp_dir}/mnt"
+	local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+
+	truncate -s -4 "${copied_bin_path}"
+}
+
+load_policy()
+{
+	local tmp_dir="$1"
+	local mount_dir="${tmp_dir}/mnt"
+
+	echo ${mount_dir}/policy_test > ${IMA_POLICY_FILE} 2> /dev/null
+}
+
 catch()
 {
 	local exit_code="$1"
@@ -105,6 +132,12 @@ main()
 		cleanup "${tmp_dir}"
 	elif [[ "${action}" == "run" ]]; then
 		run "${tmp_dir}"
+	elif [[ "${action}" == "modify-bin" ]]; then
+		modify_bin "${tmp_dir}"
+	elif [[ "${action}" == "restore-bin" ]]; then
+		restore_bin "${tmp_dir}"
+	elif [[ "${action}" == "load-policy" ]]; then
+		load_policy "${tmp_dir}"
 	else
 		echo "Unknown action: ${action}"
 		exit 1
diff --git a/tools/testing/selftests/bpf/prog_tests/test_ima.c b/tools/testing/selftests/bpf/prog_tests/test_ima.c
index 97d8a6f84f4a..b13feceb38f1 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_ima.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_ima.c
@@ -13,14 +13,17 @@
 
 #include "ima.skel.h"
 
-static int run_measured_process(const char *measured_dir, u32 *monitored_pid)
+#define MAX_SAMPLES 4
+
+static int _run_measured_process(const char *measured_dir, u32 *monitored_pid,
+				 const char *cmd)
 {
 	int child_pid, child_status;
 
 	child_pid = fork();
 	if (child_pid == 0) {
 		*monitored_pid = getpid();
-		execlp("./ima_setup.sh", "./ima_setup.sh", "run", measured_dir,
+		execlp("./ima_setup.sh", "./ima_setup.sh", cmd, measured_dir,
 		       NULL);
 		exit(errno);
 
@@ -32,19 +35,39 @@ static int run_measured_process(const char *measured_dir, u32 *monitored_pid)
 	return -EINVAL;
 }
 
-static u64 ima_hash_from_bpf;
+static int run_measured_process(const char *measured_dir, u32 *monitored_pid)
+{
+	return _run_measured_process(measured_dir, monitored_pid, "run");
+}
+
+static u64 ima_hash_from_bpf[MAX_SAMPLES];
+static int ima_hash_from_bpf_idx;
 
 static int process_sample(void *ctx, void *data, size_t len)
 {
-	ima_hash_from_bpf = *((u64 *)data);
+	if (ima_hash_from_bpf_idx >= MAX_SAMPLES)
+		return -ENOSPC;
+
+	ima_hash_from_bpf[ima_hash_from_bpf_idx++] = *((u64 *)data);
 	return 0;
 }
 
+static void test_init(struct ima__bss *bss)
+{
+	ima_hash_from_bpf_idx = 0;
+
+	bss->use_ima_file_hash = false;
+	bss->enable_bprm_creds_for_exec = false;
+	bss->enable_kernel_read_file = false;
+	bss->test_deny = false;
+}
+
 void test_test_ima(void)
 {
 	char measured_dir_template[] = "/tmp/ima_measuredXXXXXX";
 	struct ring_buffer *ringbuf = NULL;
 	const char *measured_dir;
+	u64 bin_true_sample;
 	char cmd[256];
 
 	int err, duration = 0;
@@ -72,13 +95,127 @@ void test_test_ima(void)
 	if (CHECK(err, "failed to run command", "%s, errno = %d\n", cmd, errno))
 		goto close_clean;
 
+	/*
+	 * Test #1
+	 * - Goal: obtain a sample with the bpf_ima_inode_hash() helper
+	 * - Expected result:  1 sample (/bin/true)
+	 */
+	test_init(skel->bss);
 	err = run_measured_process(measured_dir, &skel->bss->monitored_pid);
-	if (CHECK(err, "run_measured_process", "err = %d\n", err))
+	if (CHECK(err, "run_measured_process #1", "err = %d\n", err))
 		goto close_clean;
 
 	err = ring_buffer__consume(ringbuf);
 	ASSERT_EQ(err, 1, "num_samples_or_err");
-	ASSERT_NEQ(ima_hash_from_bpf, 0, "ima_hash");
+	ASSERT_NEQ(ima_hash_from_bpf[0], 0, "ima_hash");
+
+	/*
+	 * Test #2
+	 * - Goal: obtain samples with the bpf_ima_file_hash() helper
+	 * - Expected result: 2 samples (./ima_setup.sh, /bin/true)
+	 */
+	test_init(skel->bss);
+	skel->bss->use_ima_file_hash = true;
+	err = run_measured_process(measured_dir, &skel->bss->monitored_pid);
+	if (CHECK(err, "run_measured_process #2", "err = %d\n", err))
+		goto close_clean;
+
+	err = ring_buffer__consume(ringbuf);
+	ASSERT_EQ(err, 2, "num_samples_or_err");
+	ASSERT_NEQ(ima_hash_from_bpf[0], 0, "ima_hash");
+	ASSERT_NEQ(ima_hash_from_bpf[1], 0, "ima_hash");
+	bin_true_sample = ima_hash_from_bpf[1];
+
+	/*
+	 * Test #3
+	 * - Goal: confirm that bpf_ima_inode_hash() returns a non-fresh digest
+	 * - Expected result: 2 samples (/bin/true: non-fresh, fresh)
+	 */
+	test_init(skel->bss);
+
+	err = _run_measured_process(measured_dir, &skel->bss->monitored_pid,
+				    "modify-bin");
+	if (CHECK(err, "modify-bin #3", "err = %d\n", err))
+		goto close_clean;
+
+	skel->bss->enable_bprm_creds_for_exec = true;
+	err = run_measured_process(measured_dir, &skel->bss->monitored_pid);
+	if (CHECK(err, "run_measured_process #3", "err = %d\n", err))
+		goto close_clean;
+
+	err = ring_buffer__consume(ringbuf);
+	ASSERT_EQ(err, 2, "num_samples_or_err");
+	ASSERT_NEQ(ima_hash_from_bpf[0], 0, "ima_hash");
+	ASSERT_NEQ(ima_hash_from_bpf[1], 0, "ima_hash");
+	ASSERT_EQ(ima_hash_from_bpf[0], bin_true_sample, "sample_equal_or_err");
+	/* IMA refreshed the digest. */
+	ASSERT_NEQ(ima_hash_from_bpf[1], bin_true_sample,
+		   "sample_different_or_err");
+
+	/*
+	 * Test #4
+	 * - Goal: verify that bpf_ima_file_hash() returns a fresh digest
+	 * - Expected result: 4 samples (./ima_setup.sh: fresh, fresh;
+	 *                               /bin/true: fresh, fresh)
+	 */
+	test_init(skel->bss);
+	skel->bss->use_ima_file_hash = true;
+	skel->bss->enable_bprm_creds_for_exec = true;
+	err = run_measured_process(measured_dir, &skel->bss->monitored_pid);
+	if (CHECK(err, "run_measured_process #4", "err = %d\n", err))
+		goto close_clean;
+
+	err = ring_buffer__consume(ringbuf);
+	ASSERT_EQ(err, 4, "num_samples_or_err");
+	ASSERT_NEQ(ima_hash_from_bpf[0], 0, "ima_hash");
+	ASSERT_NEQ(ima_hash_from_bpf[1], 0, "ima_hash");
+	ASSERT_NEQ(ima_hash_from_bpf[2], 0, "ima_hash");
+	ASSERT_NEQ(ima_hash_from_bpf[3], 0, "ima_hash");
+	ASSERT_NEQ(ima_hash_from_bpf[2], bin_true_sample,
+		   "sample_different_or_err");
+	ASSERT_EQ(ima_hash_from_bpf[3], ima_hash_from_bpf[2],
+		  "sample_equal_or_err");
+
+	skel->bss->use_ima_file_hash = false;
+	skel->bss->enable_bprm_creds_for_exec = false;
+	err = _run_measured_process(measured_dir, &skel->bss->monitored_pid,
+				    "restore-bin");
+	if (CHECK(err, "restore-bin #3", "err = %d\n", err))
+		goto close_clean;
+
+	/*
+	 * Test #5
+	 * - Goal: obtain a sample from the kernel_read_file hook
+	 * - Expected result: 2 samples (./ima_setup.sh, policy_test)
+	 */
+	test_init(skel->bss);
+	skel->bss->use_ima_file_hash = true;
+	skel->bss->enable_kernel_read_file = true;
+	err = _run_measured_process(measured_dir, &skel->bss->monitored_pid,
+				    "load-policy");
+	if (CHECK(err, "run_measured_process #5", "err = %d\n", err))
+		goto close_clean;
+
+	err = ring_buffer__consume(ringbuf);
+	ASSERT_EQ(err, 2, "num_samples_or_err");
+	ASSERT_NEQ(ima_hash_from_bpf[0], 0, "ima_hash");
+	ASSERT_NEQ(ima_hash_from_bpf[1], 0, "ima_hash");
+
+	/*
+	 * Test #6
+	 * - Goal: ensure that the kernel_read_file hook denies an operation
+	 * - Expected result: 0 samples
+	 */
+	test_init(skel->bss);
+	skel->bss->enable_kernel_read_file = true;
+	skel->bss->test_deny = true;
+	err = _run_measured_process(measured_dir, &skel->bss->monitored_pid,
+				    "load-policy");
+	if (CHECK(!err, "run_measured_process #6", "err = %d\n", err))
+		goto close_clean;
+
+	err = ring_buffer__consume(ringbuf);
+	ASSERT_EQ(err, 0, "num_samples_or_err");
 
 close_clean:
 	snprintf(cmd, sizeof(cmd), "./ima_setup.sh cleanup %s", measured_dir);
diff --git a/tools/testing/selftests/bpf/progs/ima.c b/tools/testing/selftests/bpf/progs/ima.c
index 96060ff4ffc6..e16a2c208481 100644
--- a/tools/testing/selftests/bpf/progs/ima.c
+++ b/tools/testing/selftests/bpf/progs/ima.c
@@ -18,8 +18,12 @@ struct {
 
 char _license[] SEC("license") = "GPL";
 
-SEC("lsm.s/bprm_committed_creds")
-void BPF_PROG(ima, struct linux_binprm *bprm)
+bool use_ima_file_hash;
+bool enable_bprm_creds_for_exec;
+bool enable_kernel_read_file;
+bool test_deny;
+
+static void ima_test_common(struct file *file)
 {
 	u64 ima_hash = 0;
 	u64 *sample;
@@ -28,8 +32,12 @@ void BPF_PROG(ima, struct linux_binprm *bprm)
 
 	pid = bpf_get_current_pid_tgid() >> 32;
 	if (pid == monitored_pid) {
-		ret = bpf_ima_inode_hash(bprm->file->f_inode, &ima_hash,
-					 sizeof(ima_hash));
+		if (!use_ima_file_hash)
+			ret = bpf_ima_inode_hash(file->f_inode, &ima_hash,
+						 sizeof(ima_hash));
+		else
+			ret = bpf_ima_file_hash(file, &ima_hash,
+						sizeof(ima_hash));
 		if (ret < 0 || ima_hash == 0)
 			return;
 
@@ -43,3 +51,53 @@ void BPF_PROG(ima, struct linux_binprm *bprm)
 
 	return;
 }
+
+static int ima_test_deny(void)
+{
+	u32 pid;
+
+	pid = bpf_get_current_pid_tgid() >> 32;
+	if (pid == monitored_pid && test_deny)
+		return -EPERM;
+
+	return 0;
+}
+
+SEC("lsm.s/bprm_committed_creds")
+void BPF_PROG(bprm_committed_creds, struct linux_binprm *bprm)
+{
+	ima_test_common(bprm->file);
+}
+
+SEC("lsm.s/bprm_creds_for_exec")
+int BPF_PROG(bprm_creds_for_exec, struct linux_binprm *bprm)
+{
+	if (!enable_bprm_creds_for_exec)
+		return 0;
+
+	ima_test_common(bprm->file);
+	return 0;
+}
+
+SEC("lsm.s/kernel_read_file")
+int BPF_PROG(kernel_read_file, struct file *file, enum kernel_read_file_id id,
+	     bool contents)
+{
+	int ret;
+
+	if (!enable_kernel_read_file)
+		return 0;
+
+	if (!contents)
+		return 0;
+
+	if (id != READING_POLICY)
+		return 0;
+
+	ret = ima_test_deny();
+	if (ret < 0)
+		return ret;
+
+	ima_test_common(file);
+	return 0;
+}