linux-kernel - [PATCH] selinux: add tracepoint on denials

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Message-Id: <20200724091520.880211-1-tweek@google.com>
Date:   Fri, 24 Jul 2020 11:15:03 +0200
From:   "Thiébaud Weksteen" <tweek@...gle.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Nick Kralevich <nnk@...gle.com>,
        "Thiébaud Weksteen" <tweek@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org,
        selinux@...r.kernel.org
Subject: [PATCH] selinux: add tracepoint on denials

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@...gle.com>
Signed-off-by: Joel Fernandes <joelaf@...gle.com>
---
 MAINTAINERS                    |  1 +
 include/trace/events/selinux.h | 35 ++++++++++++++++++++++++++++++++++
 security/selinux/avc.c         |  6 ++++++
 3 files changed, 42 insertions(+)
 create mode 100644 include/trace/events/selinux.h

diff --git a/MAINTAINERS b/MAINTAINERS
index e64cdde81851..6b6cd5e13537 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15358,6 +15358,7 @@ 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..e247187a8135
--- /dev/null
+++ b/include/trace/events/selinux.h
@@ -0,0 +1,35 @@
+/* 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/ktime.h>
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(selinux_denied,
+
+	TP_PROTO(int cls, int av),
+
+	TP_ARGS(cls, av),
+
+	TP_STRUCT__entry(
+		__field(int, cls)
+		__field(int, av)
+	),
+
+	TP_fast_assign(
+		__entry->cls = cls;
+		__entry->av = av;
+	),
+
+	TP_printk("denied %d %d",
+		__entry->cls,
+		__entry->av)
+);
+
+#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..85d2e22ab656 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
@@ -672,6 +675,9 @@ static void avc_audit_pre_callback(struct audit_buffer *ab, void *a)
 		return;
 	}
 
+	if (sad->denied)
+		trace_selinux_denied(sad->tclass, av);
+
 	perms = secclass_map[sad->tclass-1].perms;
 
 	audit_log_format(ab, " {");
-- 
2.28.0.rc0.142.g3c755180ce-goog