* [PATCH v3] perf/core: Drop kernel samples even though :u is specified
@ 2017-05-25 10:09 Jin Yao
2017-06-08 9:21 ` [tip:perf/core] " tip-bot for Jin Yao
0 siblings, 1 reply; 2+ messages in thread
From: Jin Yao @ 2017-05-25 10:09 UTC (permalink / raw)
To: acme, jolsa, peterz, mingo, alexander.shishkin
Cc: Linux-kernel, ak, kan.liang, yao.jin, will.deacon, mark.rutland, Jin Yao
Change-log:
-----------
v3: Change function name skid_kernel_samples to sample_is_allowed.
Remove the new cap PERF_PMU_CAP_NO_SKID. For those PMUs without
skid, when not sampling the kernel, user_mode(regs) should always
be true. So it looks the new cap is not necessary. Remove the
checking for PERF_SAMPLE_IP. Thanks for Mark Rutland's comments.
v2: Since other arch has similar skid issue in sampling, so move the
skid checking from x86 code to generic code. Use a new flag
PERF_PMU_CAP_NO_SKID to let arch decide if keep original behavior
or drop the skid kernel samples.
-----------
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 is 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>
---
kernel/events/core.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6e75a5c..6c4e523 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7316,6 +7316,21 @@ int perf_event_account_interrupt(struct perf_event *event)
return __perf_event_account_interrupt(event, 1);
}
+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.
*/
@@ -7337,6 +7352,12 @@ static int __perf_event_overflow(struct perf_event *event,
ret = __perf_event_account_interrupt(event, throttle);
/*
+ * 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
*/
--
2.7.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [tip:perf/core] perf/core: Drop kernel samples even though :u is specified
2017-05-25 10:09 [PATCH v3] perf/core: Drop kernel samples even though :u is specified Jin Yao
@ 2017-06-08 9:21 ` tip-bot for Jin Yao
0 siblings, 0 replies; 2+ messages in thread
From: tip-bot for Jin Yao @ 2017-06-08 9:21 UTC (permalink / raw)
To: linux-tip-commits
Cc: mingo, vincent.weaver, yao.jin, stable, jolsa,
alexander.shishkin, peterz, hpa, linux-kernel, eranian, namhyung,
tglx, torvalds, acme
Commit-ID: cc1582c231ea041fbc68861dfaf957eaf902b829
Gitweb: http://git.kernel.org/tip/cc1582c231ea041fbc68861dfaf957eaf902b829
Author: Jin Yao <yao.jin@linux.intel.com>
AuthorDate: Thu, 25 May 2017 18:09:07 +0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 8 Jun 2017 10:11:50 +0200
perf/core: Drop kernel samples even though :u is specified
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: <stable@vger.kernel.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>
---
kernel/events/core.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6e75a5c..6c4e523 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7316,6 +7316,21 @@ int perf_event_account_interrupt(struct perf_event *event)
return __perf_event_account_interrupt(event, 1);
}
+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.
*/
@@ -7337,6 +7352,12 @@ static int __perf_event_overflow(struct perf_event *event,
ret = __perf_event_account_interrupt(event, throttle);
/*
+ * 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
*/
^ permalink raw reply related [flat|nested] 2+ messages in thread
end of thread, other threads:[~2017-06-08 9:25 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-05-25 10:09 [PATCH v3] perf/core: Drop kernel samples even though :u is specified Jin Yao
2017-06-08 9:21 ` [tip:perf/core] " tip-bot for Jin Yao
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).