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

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Date:	Wed, 22 May 2013 14:23:19 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Anshuman Khandual <khandual@...ux.vnet.ibm.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

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.
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