linux-kernel - Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict with VMX

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 14 Feb 2017 18:17:30 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        vince@...ter.net, eranian@...gle.com,
        Arnaldo Carvalho de Melo <acme@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict with VMX

Peter Zijlstra <peterz@...radead.org> writes:

> On Tue, Feb 14, 2017 at 03:24:15PM +0200, Alexander Shishkin wrote:
>> At the moment, if VMX operation prevents PT tracing, the PMU will
>> silently return success to the event scheduling code, which will
>> track its 'on' time, etc. Instead, report failure so that perf
>> core knows this event is not actually on.
>> 
>> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
>> Reported-by: Andi Kleen <ak@...ux.intel.com>
>> Fixes: 1c5ac21a0e ("perf/x86/intel/pt: Don't die on VMXON")
>> ---
>>  arch/x86/events/intel/pt.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
>> index d92a60ef08..9372fa4549 100644
>> --- a/arch/x86/events/intel/pt.c
>> +++ b/arch/x86/events/intel/pt.c
>> @@ -1335,7 +1335,7 @@ static void pt_event_start(struct perf_event *event, int mode)
>>  	struct pt_buffer *buf;
>>  
>>  	if (READ_ONCE(pt->vmx_on))
>> -		return;
>> +		goto fail_stop;
>>  
>>  	buf = perf_aux_output_begin(&pt->handle, event);
>>  	if (!buf)
>
> I'm not getting it; how does this matter to the time tracking in
> event_sched_in() / event_sched_out() ?
>
> That looks at event->state == PERF_EVENT_STATE*
>
> This goto affects event->hw.state == PERF_HES_
>
> The core assumes ->start() will _NOT_ fail.

This is called by pmu::add(), which checks hw.state afterwards and if it
finds HES_STOPPED, it returns an error, which event_sched_in() captures
and keeps the event in INACTIVE state. Should I add a comment about it?

Regards,
--
Alex