Subject: Re: [PATCH 3/3] perf, x86, lbr: Demand proper privileges for PERF_SAMPLE_BRANCH_KERNEL

From: Michael Neuling <[email-masked]>
Date: Thu, 16 May 2013 20:15:17 +1000

Peter Zijlstra <[email-masked]> wrote:

> On Wed, May 15, 2013 at 03:37:22PM +0200, Stephane Eranian wrote:
> > On Fri, May 3, 2013 at 2:11 PM, Peter Zijlstra <[email-masked]> wrote:
> > > We should always have proper privileges when requesting kernel data.
> > >
> > > Cc: Andi Kleen <[email-masked]>
> > > Cc: [email-masked]
> > > Signed-off-by: Peter Zijlstra <[email-masked]>
> > > Link: http://lkml.kernel.org/n/[email-masked]
> > > ---
> > >  arch/x86/kernel/cpu/perf_event_intel_lbr.c |    5 ++++-
> > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > --- 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_filte
> > >         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;
> > >                 mask |= X86_BR_KERNEL;
> > > +       }
> > >
> > This will prevent regular users from capturing kernel -> kernel branches.
> > But it won't prevent users from getting kernel -> user branches. Thus
> > some kernel address will still be captured. I guess they could be eliminated
> > by the sw_filter.
> > 
> > When using LBR priv level filtering, the filter applies to the branch target
> > only.
> 
> How about something like the below? It also adds the branch flags
> Mikey wanted for PowerPC.

Peter,

BTW PowerPC also has the ability to filter on conditional branches.  Any
chance we could add something like the follow to perf also?

Mikey

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index fb104e5..891c769 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -157,8 +157,9 @@ enum perf_branch_sample_type {
 	PERF_SAMPLE_BRANCH_ANY_CALL	= 1U << 4, /* any call branch */
 	PERF_SAMPLE_BRANCH_ANY_RETURN	= 1U << 5, /* any return branch */
 	PERF_SAMPLE_BRANCH_IND_CALL	= 1U << 6, /* indirect calls */
+	PERF_SAMPLE_BRANCH_CONDITIONAL  = 1U << 7, /* conditional branches */
 
-	PERF_SAMPLE_BRANCH_MAX		= 1U << 7, /* non-ABI */
+	PERF_SAMPLE_BRANCH_MAX		= 1U << 8, /* non-ABI */
 };
 
 #define PERF_SAMPLE_BRANCH_PLM_ALL \
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index cdf58ec..5b0b89d 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -676,6 +676,7 @@ static const struct branch_mode branch_modes[] = {
 	BRANCH_OPT("any_call", PERF_SAMPLE_BRANCH_ANY_CALL),
 	BRANCH_OPT("any_ret", PERF_SAMPLE_BRANCH_ANY_RETURN),
 	BRANCH_OPT("ind_call", PERF_SAMPLE_BRANCH_IND_CALL),
+	BRANCH_OPT("cnd", PERF_SAMPLE_BRANCH_CONDITIONAL),
 	BRANCH_END
 };