[lkml]   [2008]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
SubjectRe: [patch] Performance Counters for Linux, v4

* Pavel Machek <> wrote:

> Hmm, if I timec some setuid program, what happens?

yes, i already had a quick look at that a few days ago when i implemented
counter inheritance (for different reasons) and couldnt find the cleanest
place to put the exec() flushing into so i procrastinated that a bit :)

> Performance counters seem like great tool to pull secret keys out of
> other processes :-).

if you worry about _that_ angle you also have to:

- turn off the cycle counter

- turn off precise utimes

- plus you have to forbid SMT CPUs as well. On HT a task could
co-schedule with your setuid task and observe its timing
characteristics via its _own_ behavior. (which is impacted by whatever
is running on another SMT/HT thread.)

the real exec() worry are: active, IRQ driven samples/events. Not possible
yet via the current iteration of counter inheritance (hence my
procrastination) - but it makes sense and that's why i was looking at the
exec() angle.

and that will flush simple counters too, removing your theoretical attack
angle as well.

So how about the patch below?


Subject: perfcounters: flush on setuid exec
From: Ingo Molnar <>
Date: Tue Dec 16 13:40:44 CET 2008

Pavel Machek pointed out that performance counters should be flushed
when crossing protection domains on setuid execution.

Reported-by: Pavel Machek <>
Signed-off-by: Ingo Molnar <>
fs/exec.c | 8 ++++++++
1 file changed, 8 insertions(+)

Index: linux/fs/exec.c
--- linux.orig/fs/exec.c
+++ linux/fs/exec.c
@@ -33,6 +33,7 @@
#include <linux/string.h>
#include <linux/init.h>
#include <linux/pagemap.h>
+#include <linux/perf_counter.h>
#include <linux/highmem.h>
#include <linux/spinlock.h>
#include <linux/key.h>
@@ -1015,6 +1016,13 @@ int flush_old_exec(struct linux_binprm *
set_dumpable(current->mm, suid_dumpable);

+ /*
+ * Flush performance counters when crossing a
+ * security domain:
+ */
+ if (!get_dumpable(current->mm))
+ perf_counter_exit_task(current);
/* An exec changes our domain. We are no longer part of the thread
group */

 \ /
  Last update: 2008-12-16 13:55    [W:0.184 / U:0.096 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site