[PATCH v2] selinux: add tracepoint on denials

["Thiébaud Weksteen" <tweek@google.com>]

The audit data currently captures which process and which target
is responsible for a denial. There is no data on where exactly in the
process that call occurred. Debugging can be made easier by being able to
reconstruct the unified kernel and userland stack traces [1]. Add a
tracepoint on the SELinux denials which can then be used by userland
(i.e. perf).

Although this patch could manually be added by each OS developer to
trouble shoot a denial, adding it to the kernel streamlines the
developers workflow.

[1] https://source.android.com/devices/tech/debug/native_stack_dump

Signed-off-by: Thiébaud Weksteen <tweek@google.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>
---
Changes in v2:
- Replace %d formatter with %x
- Replace TRACE_EVENT with TRACE_EVENT_CONDITION
- Add pid to structure and printk
- Rename structure fields for clarity


 MAINTAINERS                    |  1 +
 include/trace/events/selinux.h | 39 ++++++++++++++++++++++++++++++++++
 security/selinux/avc.c         |  5 +++++
 3 files changed, 45 insertions(+)
 create mode 100644 include/trace/events/selinux.h

diff --git a/MAINTAINERS b/MAINTAINERS
index f0569cf304ca..0f74c8f073ab 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15369,6 +15369,7 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/selinux.git
 F:	Documentation/ABI/obsolete/sysfs-selinux-checkreqprot
 F:	Documentation/ABI/obsolete/sysfs-selinux-disable
 F:	Documentation/admin-guide/LSM/SELinux.rst
+F:	include/trace/events/selinux.h
 F:	include/uapi/linux/selinux_netlink.h
 F:	scripts/selinux/
 F:	security/selinux/
diff --git a/include/trace/events/selinux.h b/include/trace/events/selinux.h
new file mode 100644
index 000000000000..287e1ecb4451
--- /dev/null
+++ b/include/trace/events/selinux.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM selinux
+
+#if !defined(_TRACE_SELINUX_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SELINUX_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT_CONDITION(selinux_denied,
+
+	TP_PROTO(struct selinux_audit_data *sad, pid_t pid),
+
+	TP_ARGS(sad, pid),
+
+	TP_CONDITION(sad->denied),
+
+	TP_STRUCT__entry(
+		__field(pid_t, pid)
+		__field(int, tclass)
+		__field(int, audited)
+	),
+
+	TP_fast_assign(
+		__entry->pid = pid;
+		__entry->tclass = sad->tclass;
+		__entry->audited = sad->audited;
+	),
+
+	TP_printk("denied pid=%d tclass=%x audited=%x",
+		__entry->pid,
+		__entry->tclass,
+		__entry->audited)
+);
+
+#endif
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index d18cb32a242a..ca8206f38d8a 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -31,6 +31,9 @@
 #include "avc_ss.h"
 #include "classmap.h"
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/selinux.h>
+
 #define AVC_CACHE_SLOTS			512
 #define AVC_DEF_CACHE_THRESHOLD		512
 #define AVC_CACHE_RECLAIM		16
@@ -665,6 +668,8 @@ static void avc_audit_pre_callback(struct audit_buffer *ab, void *a)
 	const char **perms;
 	int i, perm;
 
+	trace_selinux_denied(sad, task_tgid_nr(current));
+
 	audit_log_format(ab, "avc:  %s ", sad->denied ? "denied" : "granted");
 
 	if (av == 0) {
-- 
2.28.0.rc0.142.g3c755180ce-goog