linux-kernel - Re: [PATCH 3/3] perf, x86, lbr: Demand proper privileges for PERF_SAMPLE_BRANCH

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Message-ID: <519CDB6E.6020508@linux.vnet.ibm.com>
Date:	Wed, 22 May 2013 20:21:26 +0530
From:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	Michael Neuling <mikey@...ling.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PPC dev <linuxppc-dev@...abs.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 3/3] perf, x86, lbr: Demand proper privileges for PERF_SAMPLE_BRANCH_KERNEL

On 05/22/2013 05:53 PM, Stephane Eranian wrote:
> Hi,
> 
> 
> 
> On Wed, May 22, 2013 at 8:43 AM, Anshuman Khandual
> <khandual@...ux.vnet.ibm.com> wrote:
>> On 05/21/2013 07:25 PM, Stephane Eranian wrote:
>>> On Thu, May 16, 2013 at 12:15 PM, Michael Neuling <mikey@...ling.org> wrote:
>>>> Peter Zijlstra <peterz@...radead.org> 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 <a.p.zijlstra@...llo.nl> wrote:
>>>>>>> We should always have proper privileges when requesting kernel data.
>>>>>>>
>>>>>>> Cc: Andi Kleen <ak@...ux.intel.com>
>>>>>>> Cc: eranian@...gle.com
>>>>>>> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>>>>>>> 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(-)
>>>>>>>
>>>>>>> --- 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 */
>>>>
>>> I would use PERF_SAMPLE_BRANCH_COND here.
>>>
>>>> -       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),
>>>
>>> use "cond"
>>>
>>>>         BRANCH_END
>>>>  };
>>>>
>>>
>>> And if you do this, you also need to update the x86
>>> perf_event_intel_lbr.c mapping
>>> tables to fill out the entries for PERF_SAMPLE_BRANCH_COND:
>>>
>>>         [PERF_SAMPLE_BRANCH_COND]       = LBR_JCC,
>>>
>>> And you also need to update intel_pmu_setup_sw_lbr_filter()
>>> to handle the conversion to x86 instructions:
>>>
>>>        if (br_type & PERF_SAMPLE_BRANCH_COND)
>>>                 mask |= X86_BR_JCC;
>>>
>>>
>>> You also need to update the perf-record.txt documentation to list cond
>>> as a possible
>>> branch filter.
>>
>> Hey Stephane,
>>
>> I have incorporated all the review comments into the patch series
>> https://lkml.org/lkml/2013/5/22/51.
>>
> I don't see how you can compile Patch 3/5:
> 
> + BRANCH_OPT("cond", PERF_SAMPLE_BRANCH_CONDITIONAL),
> 
> Needs to be PERF_SAMPLE_BRANCH_COND.
> 

Ahh, sorry missed it, will fix it.

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