Commit d2878d64 authored Aug 31, 2015 by Alexander Shishkin Committed by Ingo Molnar Sep 13, 2015

perf/x86/intel/bts: Disallow use by unprivileged users on paranoid systems



BTS leaks kernel addresses even in userspace-only mode due to imprecise IP
sampling, so sometimes syscall entry points or page fault handler addresses
end up in a userspace trace.

Now, intel_bts driver exports trace data zero-copy, it does not scan through
it to filter out the kernel addresses and it's would be a O(n) job.

To work around this situation, this patch forbids the use of intel_bts
driver by unprivileged users on systems with the paranoid setting above the
(kernel's) default "1", which still allows kernel profiling. In other words,
using intel_bts driver implies kernel tracing, regardless of the
"exclude_kernel" attribute setting.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.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: hpa@zytor.com
Link: http://lkml.kernel.org/r/1441030168-6853-3-git-send-email-alexander.shishkin@linux.intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent a09d31f4

arch/x86/kernel/cpu/perf_event_intel_bts.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -495,6 +495,19 @@ static int bts_event_init(struct perf_event *event)
		if (x86_add_exclusive(x86_lbr_exclusive_bts))
		return -EBUSY;

		/*
		* BTS leaks kernel addresses even when CPL0 tracing is
		* disabled, so disallow intel_bts driver for unprivileged
		* users on paranoid systems since it provides trace data
		* to the user in a zero-copy fashion.
		*
		* Note that the default paranoia setting permits unprivileged
		* users to profile the kernel.
		*/
		if (event->attr.exclude_kernel && perf_paranoid_kernel() &&
		!capable(CAP_SYS_ADMIN))
		return -EACCES;

		ret = x86_reserve_hardware();
		if (ret) {
		x86_del_exclusive(x86_lbr_exclusive_bts);