From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751972AbbH1Fbf (ORCPT ); Fri, 28 Aug 2015 01:31:35 -0400 Received: from mail-wi0-f172.google.com ([209.85.212.172]:34227 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751812AbbH1Fbe (ORCPT ); Fri, 28 Aug 2015 01:31:34 -0400 Date: Fri, 28 Aug 2015 07:31:30 +0200 From: Ingo Molnar To: Alexander Shishkin Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Arnaldo Carvalho de Melo Subject: Re: [PATCH 2/2] perf/x86/intel/bts: Disallow use by unprivileged users on paranoid systems Message-ID: <20150828053130.GC26741@gmail.com> References: <1440688422-27954-1-git-send-email-alexander.shishkin@linux.intel.com> <1440688422-27954-3-git-send-email-alexander.shishkin@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1440688422-27954-3-git-send-email-alexander.shishkin@linux.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Alexander Shishkin wrote: > 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 with paranoid setting higher than 1, which > forbids kernel tracing. > > Signed-off-by: Alexander Shishkin > --- > arch/x86/kernel/cpu/perf_event_intel_bts.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/x86/kernel/cpu/perf_event_intel_bts.c b/arch/x86/kernel/cpu/perf_event_intel_bts.c > index 80df16e020..4f6daff92d 100644 > --- a/arch/x86/kernel/cpu/perf_event_intel_bts.c > +++ b/arch/x86/kernel/cpu/perf_event_intel_bts.c > @@ -495,6 +495,16 @@ 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. > + */ > + if (event->attr.exclude_kernel && perf_paranoid_kernel() && > + !capable(CAP_SYS_ADMIN)) > + return -EACCES; I.e. it's disabled by default as well, with default paranoia settings? Thanks, Ingo