[tip:perf/core] perf/x86/intel/bts: Disallow use by unprivileged users on paranoid systems

[tip-bot for Alexander Shishkin]

Commit-ID:  d2878d642a4edd1d57c691dc3e4d7847cbf9d442
Gitweb:     http://git.kernel.org/tip/d2878d642a4edd1d57c691dc3e4d7847cbf9d442
Author:     Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
AuthorDate: Mon, 31 Aug 2015 17:09:28 +0300
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sun, 13 Sep 2015 11:27:22 +0200

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@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: hpa@xxxxxxxxx
Link: http://lkml.kernel.org/r/1441030168-6853-3-git-send-email-alexander.shishkin@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/cpu/perf_event_intel_bts.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_bts.c b/arch/x86/kernel/cpu/perf_event_intel_bts.c
index d1c0f25..2cad71d 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_bts.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_bts.c
@@ -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);
--
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