linux-kernel - Re: [tip:perf/urgent] perf/x86/intel/lbr: Demand proper privileges for PERF_SAMPLE_BRANCH

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Date:	Sun, 5 May 2013 11:05:04 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	a.p.zijlstra@...llo.nl, hpa@...or.com,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	ak@...ux.intel.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf/x86/intel/lbr: Demand proper privileges
 for PERF_SAMPLE_BRANCH_KERNEL


* Borislav Petkov <bp@...en8.de> wrote:

> On Sat, May 04, 2013 at 01:22:57AM -0700, tip-bot for Peter Zijlstra wrote:
> > Commit-ID:  0f5c78b5f33ce940034743e5f9485fc81ad75b0f
> > Gitweb:     http://git.kernel.org/tip/0f5c78b5f33ce940034743e5f9485fc81ad75b0f
> > Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > AuthorDate: Fri, 3 May 2013 14:11:25 +0200
> > Committer:  Ingo Molnar <mingo@...nel.org>
> > CommitDate: Sat, 4 May 2013 08:37:48 +0200
> > 
> > perf/x86/intel/lbr: Demand proper privileges for PERF_SAMPLE_BRANCH_KERNEL
> > 
> > We should always have proper privileges when requesting kernel
> > data.
> > 
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Cc: <stable@...nel.org>
> > Cc: Andi Kleen <ak@...ux.intel.com>
> > Cc: eranian@...gle.com
> > Link: http://lkml.kernel.org/r/20130503121256.230745028@chello.nl
> > Signed-off-by: Ingo Molnar <mingo@...nel.org>
> > Link: http://lkml.kernel.org/n/tip-v0x9ky3ahzr6nm3c6ilwrili@git.kernel.org
> > ---
> >  arch/x86/kernel/cpu/perf_event_intel_lbr.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> > index de341d4..0e92871 100644
> > --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> > +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> > @@ -318,8 +318,11 @@ static void intel_pmu_setup_sw_lbr_filter(struct perf_event *event)
> >  	if (br_type & PERF_SAMPLE_BRANCH_USER)
> >  		mask |= X86_BR_USER;
> >  
> > -	if (br_type & PERF_SAMPLE_BRANCH_KERNEL)
> > +	if (br_type & PERF_SAMPLE_BRANCH_KERNEL) {
> > +		if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
> > +			return -EACCES;
> 
> It is probably not too late to amend this patch and remove the "-EACCES":
> 
> arch/x86/kernel/cpu/perf_event_intel_lbr.c: In function ???intel_pmu_setup_sw_lbr_filter???:
> arch/x86/kernel/cpu/perf_event_intel_lbr.c:323:4: warning: ???return??? with a value, in function returning void [enabled by default]

Well, the better fix is to propagate that error condition down instead of 
ignoring it.

Since it was the head commit for a tree others don't typically pull and 
base development work off I amended it.

Thanks,

	Ingo
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