[kernel-hardening] [PATCH 1/2] security, perf: allow further restriction of perf_event_open

[Jeff Vander Stoep <jeffv@google.com>]

When kernel.perf_event_paranoid is set to 3 (or greater), disallow
all access to performance events by users without CAP_SYS_ADMIN.

This new level of restriction is intended to reduce the attack
surface of the kernel. Perf is a valuable tool for developers but
is generally unnecessary and unused on production systems. Perf may
open up an attack vector to vulnerable device-specific drivers as
recently demonstrated in CVE-2016-0805, CVE-2016-0819,
CVE-2016-0843, CVE-2016-3768, and CVE-2016-3843. This new level of
restriction allows for a safe default to be set on production systems
while leaving a simple means for developers to grant access [1].

This feature is derived from CONFIG_GRKERNSEC_PERF_HARDEN by Brad
Spengler. It is based on a patch by Ben Hutchings [2]. Ben's patches
have been modified and split up to address on-list feedback.

kernel.perf_event_paranoid=3 is the default on both Debian [2] and
Android [3].

[1] Making perf available to developers on Android:
https://android-review.googlesource.com/#/c/234400/
[2] Original patch by Ben Hutchings:
https://lkml.org/lkml/2016/1/11/587
[3] https://android-review.googlesource.com/#/c/234743/

Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
---
 Documentation/sysctl/kernel.txt | 1 +
 include/linux/perf_event.h      | 5 +++++
 kernel/events/core.c            | 4 ++++
 3 files changed, 10 insertions(+)

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index ffab8b5..fac9798 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -665,6 +665,7 @@ users (without CAP_SYS_ADMIN).  The default value is 2.
 >=0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
 >=1: Disallow CPU event access by users without CAP_SYS_ADMIN
 >=2: Disallow kernel profiling by users without CAP_SYS_ADMIN
+>=3: Disallow all event access by users without CAP_SYS_ADMIN
 
 ==============================================================
 
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 8ed43261..1e2080f 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1156,6 +1156,11 @@ static inline bool perf_paranoid_kernel(void)
 	return sysctl_perf_event_paranoid > 1;
 }
 
+static inline bool perf_paranoid_any(void)
+{
+	return sysctl_perf_event_paranoid > 2;
+}
+
 extern void perf_event_init(void);
 extern void perf_tp_event(u16 event_type, u64 count, void *record,
 			  int entry_size, struct pt_regs *regs,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 356a6c7..52bd100 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -353,6 +353,7 @@ static struct srcu_struct pmus_srcu;
  *   0 - disallow raw tracepoint access for unpriv
  *   1 - disallow cpu events for unpriv
  *   2 - disallow kernel profiling for unpriv
+ *   3 - disallow all unpriv perf event use
  */
 int sysctl_perf_event_paranoid __read_mostly = 2;
 
@@ -9296,6 +9297,9 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (flags & ~PERF_FLAG_ALL)
 		return -EINVAL;
 
+	if (perf_paranoid_any() && !capable(CAP_SYS_ADMIN))
+				return -EACCES;
+
 	err = perf_copy_attr(attr_uptr, &attr);
 	if (err)
 		return err;
-- 
2.8.0.rc3.226.g39d4020