linux-kernel - Re: perf with precise attribute kills all KVM based VMs

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]

Message-ID: <20120711095337.GJ23898@redhat.com>
Date:	Wed, 11 Jul 2012 12:53:37 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	David Ahern <dsahern@...il.com>, Avi Kivity <avi@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf with precise attribute kills all KVM based VMs

On Wed, Jul 11, 2012 at 11:49:47AM +0200, Peter Zijlstra wrote:
> On Wed, 2012-07-11 at 10:10 +0300, Gleb Natapov wrote:
> 
> > Looks like Avi is right about the overshoot. Can you test something like this?
> > 
> > diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
> > index 166546e..5fb371a 100644
> > --- a/arch/x86/kernel/cpu/perf_event_intel.c
> > +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> > @@ -1374,8 +1374,11 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr)
> >  	arr[0].msr = MSR_CORE_PERF_GLOBAL_CTRL;
> >  	arr[0].host = x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_guest_mask;
> >  	arr[0].guest = x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_host_mask;
> > +	arr[1].msr = MSR_IA32_PEBS_ENABLE;
> > +	arr[1].host = cpuc->pebs_enabled;
> > +	arr[1].guest = 0;
> > +	*nr = 2;
> >  
> > -	*nr = 1;
> >  	return arr;
> >  }
> 
> 
> You also need to clear TR, BTS, BTINT from MSR_IA32_DEBUGCTLMSR and
> ideally you'd also clear MSR_IA32_DS_AREA so that any write will be a
> proper NULL deref or such.
Yes. With the patch above :pp modifier does not crash guest for me, but
in theory it should since BTS are still written to DS. May be BTS writes do
not overshoot guest entry. Will have to ask Intel for clarification.

--
			Gleb.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/