* Patch "perf/core: Drop kernel samples even though :u is specified" has been added to the 4.9-stable tree
@ 2017-06-12 12:51 gregkh
0 siblings, 0 replies; only message in thread
From: gregkh @ 2017-06-12 12:51 UTC (permalink / raw)
To: yao.jin, acme, alexander.shishkin, eranian, gregkh, jolsa, mingo,
namhyung, peterz, tglx, torvalds, vincent.weaver
Cc: stable, stable-commits
This is a note to let you know that I've just added the patch titled
perf/core: Drop kernel samples even though :u is specified
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-core-drop-kernel-samples-even-though-u-is-specified.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.
>From cc1582c231ea041fbc68861dfaf957eaf902b829 Mon Sep 17 00:00:00 2001
From: Jin Yao <yao.jin@linux.intel.com>
Date: Thu, 25 May 2017 18:09:07 +0800
Subject: perf/core: Drop kernel samples even though :u is specified
From: Jin Yao <yao.jin@linux.intel.com>
commit cc1582c231ea041fbc68861dfaf957eaf902b829 upstream.
When doing sampling, for example:
perf record -e cycles:u ...
On workloads that do a lot of kernel entry/exits we see kernel
samples, even though :u is specified. This is due to skid existing.
This might be a security issue because it can leak kernel addresses even
though kernel sampling support is disabled.
The patch drops the kernel samples if exclude_kernel is specified.
For example, test on Haswell desktop:
perf record -e cycles:u <mgen>
perf report --stdio
Before patch applied:
99.77% mgen mgen [.] buf_read
0.20% mgen mgen [.] rand_buf_init
0.01% mgen [kernel.vmlinux] [k] apic_timer_interrupt
0.00% mgen mgen [.] last_free_elem
0.00% mgen libc-2.23.so [.] __random_r
0.00% mgen libc-2.23.so [.] _int_malloc
0.00% mgen mgen [.] rand_array_init
0.00% mgen [kernel.vmlinux] [k] page_fault
0.00% mgen libc-2.23.so [.] __random
0.00% mgen libc-2.23.so [.] __strcasestr
0.00% mgen ld-2.23.so [.] strcmp
0.00% mgen ld-2.23.so [.] _dl_start
0.00% mgen libc-2.23.so [.] sched_setaffinity@@GLIBC_2.3.4
0.00% mgen ld-2.23.so [.] _start
We can see kernel symbols apic_timer_interrupt and page_fault.
After patch applied:
99.79% mgen mgen [.] buf_read
0.19% mgen mgen [.] rand_buf_init
0.00% mgen libc-2.23.so [.] __random_r
0.00% mgen mgen [.] rand_array_init
0.00% mgen mgen [.] last_free_elem
0.00% mgen libc-2.23.so [.] vfprintf
0.00% mgen libc-2.23.so [.] rand
0.00% mgen libc-2.23.so [.] __random
0.00% mgen libc-2.23.so [.] _int_malloc
0.00% mgen libc-2.23.so [.] _IO_doallocbuf
0.00% mgen ld-2.23.so [.] do_lookup_x
0.00% mgen ld-2.23.so [.] open_verify.constprop.7
0.00% mgen ld-2.23.so [.] _dl_important_hwcaps
0.00% mgen libc-2.23.so [.] sched_setaffinity@@GLIBC_2.3.4
0.00% mgen ld-2.23.so [.] _start
There are only userspace symbols.
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Cc: jolsa@kernel.org
Cc: kan.liang@intel.com
Cc: mark.rutland@arm.com
Cc: will.deacon@arm.com
Cc: yao.jin@intel.com
Link: http://lkml.kernel.org/r/1495706947-3744-1-git-send-email-yao.jin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/events/core.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7062,6 +7062,21 @@ static void perf_log_itrace_start(struct
perf_output_end(&handle);
}
+static bool sample_is_allowed(struct perf_event *event, struct pt_regs *regs)
+{
+ /*
+ * Due to interrupt latency (AKA "skid"), we may enter the
+ * kernel before taking an overflow, even if the PMU is only
+ * counting user events.
+ * To avoid leaking information to userspace, we must always
+ * reject kernel samples when exclude_kernel is set.
+ */
+ if (event->attr.exclude_kernel && !user_mode(regs))
+ return false;
+
+ return true;
+}
+
/*
* Generic event overflow handling, sampling.
*/
@@ -7109,6 +7124,12 @@ static int __perf_event_overflow(struct
}
/*
+ * For security, drop the skid kernel samples if necessary.
+ */
+ if (!sample_is_allowed(event, regs))
+ return ret;
+
+ /*
* XXX event_limit might not quite work as expected on inherited
* events
*/
Patches currently in stable-queue which might be from yao.jin@linux.intel.com are
queue-4.9/perf-core-drop-kernel-samples-even-though-u-is-specified.patch
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2017-06-12 12:51 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-06-12 12:51 Patch "perf/core: Drop kernel samples even though :u is specified" has been added to the 4.9-stable tree gregkh
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.