Commit 2eece390 authored Oct 23, 2017 by Alexander Shishkin Committed by Ingo Molnar Oct 24, 2017

perf/x86/intel/bts: Fix exclusive event reference leak



Commit:

  d2878d64 ("perf/x86/intel/bts: Disallow use by unprivileged users on paranoid systems")

... adds a privilege check in the exactly wrong place in the event init path:
after the 'LBR exclusive' reference has been taken, and doesn't release it
in the case of insufficient privileges. After this, nobody in the system
gets to use PT or LBR afterwards.

This patch moves the privilege check to where it should have been in the
first place.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: d2878d64 ("perf/x86/intel/bts: Disallow use by unprivileged users on paranoid systems")
Link: http://lkml.kernel.org/r/20171023123533.16973-1-alexander.shishkin@linux.intel.com


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

parent 6cff0a11

arch/x86/events/intel/bts.c

+3 −3

Original line number	Original line	Diff line number	Diff line
	@@ -546,9 +546,6 @@ static int bts_event_init(struct perf_event *event)
	if (event->attr.type != bts_pmu.type)		if (event->attr.type != bts_pmu.type)
	return -ENOENT;		return -ENOENT;

	if (x86_add_exclusive(x86_lbr_exclusive_bts))
	return -EBUSY;

	/*		/*
	* BTS leaks kernel addresses even when CPL0 tracing is		* BTS leaks kernel addresses even when CPL0 tracing is
	* disabled, so disallow intel_bts driver for unprivileged		* disabled, so disallow intel_bts driver for unprivileged
	@@ -562,6 +559,9 @@ static int bts_event_init(struct perf_event *event)
	!capable(CAP_SYS_ADMIN))		!capable(CAP_SYS_ADMIN))
	return -EACCES;		return -EACCES;

			if (x86_add_exclusive(x86_lbr_exclusive_bts))
			return -EBUSY;

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