[PATCH bpf-next v3 09/10] bpf: lsm: Add selftests for BPF_PROG_TYPE_LSM

[KP Singh]

From: KP Singh <kpsingh at google.com>

* Load a BPF program that audits mprotect calls
* Attach the program to the "file_mprotect" LSM hook.
* Do an mprotect on some memory allocated on the heap
* Verify if the audit event was received using the shared global
  result variable.

Signed-off-by: KP Singh <kpsingh at google.com>
Reviewed-by: Brendan Jackman <jackmanb at google.com>
Reviewed-by: Florent Revest <revest at google.com>
Reviewed-by: Thomas Garnier <thgarnie at google.com>
---
 MAINTAINERS                                   |  3 +
 tools/testing/selftests/bpf/lsm_helpers.h     | 19 ++++++
 .../bpf/prog_tests/lsm_mprotect_audit.c       | 58 +++++++++++++++++++
 .../selftests/bpf/progs/lsm_mprotect_audit.c  | 47 +++++++++++++++
 4 files changed, 127 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/lsm_helpers.h
 create mode 100644 tools/testing/selftests/bpf/prog_tests/lsm_mprotect_audit.c
 create mode 100644 tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c

diff --git a/MAINTAINERS b/MAINTAINERS
index c606b3d89992..32236d89d00b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3210,6 +3210,9 @@ L:	bpf at vger.kernel.org
 S:	Maintained
 F:	security/bpf/
 F:	include/linux/bpf_lsm.h
+F:	tools/testing/selftests/bpf/lsm_helpers.h
+F:	tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c
+F:	tools/testing/selftests/bpf/prog_tests/lsm_mprotect_audit.c
 
 BROADCOM B44 10/100 ETHERNET DRIVER
 M:	Michael Chan <michael.chan at broadcom.com>
diff --git a/tools/testing/selftests/bpf/lsm_helpers.h b/tools/testing/selftests/bpf/lsm_helpers.h
new file mode 100644
index 000000000000..8bad08f77654
--- /dev/null
+++ b/tools/testing/selftests/bpf/lsm_helpers.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright 2019 Google LLC.
+ */
+#ifndef _LSM_HELPERS_H
+#define _LSM_HELPERS_H
+
+struct lsm_mprotect_audit_result {
+	/* This ensures that the LSM Hook only monitors the PID requested
+	 * by the loader
+	 */
+	__u32 monitored_pid;
+	/* The number of mprotect calls for the monitored PID.
+	 */
+	__u32 mprotect_count;
+};
+
+#endif /* _LSM_HELPERS_H */
diff --git a/tools/testing/selftests/bpf/prog_tests/lsm_mprotect_audit.c b/tools/testing/selftests/bpf/prog_tests/lsm_mprotect_audit.c
new file mode 100644
index 000000000000..ff90b874eafc
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/lsm_mprotect_audit.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2019 Google LLC.
+ */
+
+#include <test_progs.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <malloc.h>
+#include "lsm_helpers.h"
+#include "lsm_mprotect_audit.skel.h"
+
+int heap_mprotect(void)
+{
+	void *buf;
+	long sz;
+
+	sz = sysconf(_SC_PAGESIZE);
+	if (sz < 0)
+		return sz;
+
+	buf = memalign(sz, 2 * sz);
+	if (buf == NULL)
+		return -ENOMEM;
+
+	return mprotect(buf, sz, PROT_READ | PROT_EXEC);
+}
+
+void test_lsm_mprotect_audit(void)
+{
+	struct lsm_mprotect_audit_result *result;
+	struct lsm_mprotect_audit *skel = NULL;
+	int err, duration = 0;
+
+	skel = lsm_mprotect_audit__open_and_load();
+	if (CHECK(!skel, "skel_load", "lsm_mprotect_audit skeleton failed\n"))
+		goto close_prog;
+
+	err = lsm_mprotect_audit__attach(skel);
+	if (CHECK(err, "attach", "lsm_mprotect_audit attach failed: %d\n", err))
+		goto close_prog;
+
+	result = &skel->bss->result;
+	result->monitored_pid = getpid();
+
+	err = heap_mprotect();
+	if (CHECK(err < 0, "heap_mprotect", "err %d errno %d\n", err, errno))
+		goto close_prog;
+
+	/* Make sure mprotect_audit program was triggered
+	 * and detected an mprotect on the heap.
+	 */
+	CHECK_FAIL(result->mprotect_count != 1);
+
+close_prog:
+	lsm_mprotect_audit__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c b/tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c
new file mode 100644
index 000000000000..231cd64fd0f7
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2019 Google LLC.
+ */
+
+#include <linux/bpf.h>
+#include <stdbool.h>
+#include "bpf_trace_helpers.h"
+#include "lsm_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct lsm_mprotect_audit_result result = {
+	.mprotect_count = 0,
+	.monitored_pid = 0,
+};
+
+/*
+ * Define some of the structs used in the BPF program.
+ * Only the field names and their sizes need to be the
+ * same as the kernel type, the order is irrelevant.
+ */
+struct mm_struct {
+	unsigned long start_brk, brk;
+} __attribute__((preserve_access_index));
+
+struct vm_area_struct {
+	unsigned long vm_start, vm_end;
+	struct mm_struct *vm_mm;
+} __attribute__((preserve_access_index));
+
+SEC("lsm/file_mprotect")
+int BPF_PROG(mprotect_audit, struct vm_area_struct *vma,
+	     unsigned long reqprot, unsigned long prot)
+{
+	__u32 pid = bpf_get_current_pid_tgid();
+	int is_heap = 0;
+
+	is_heap = (vma->vm_start >= vma->vm_mm->start_brk &&
+		   vma->vm_end <= vma->vm_mm->brk);
+
+	if (is_heap && result.monitored_pid == pid)
+		result.mprotect_count++;
+
+	return 0;
+}
-- 
2.20.1