linux-kernel - Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods

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: <20090616083635.GE16229@elte.hu>
Date:	Tue, 16 Jun 2009 10:36:35 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, paulus@...ba.org, acme@...hat.com,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	penberg@...helsinki.fi, vegard.nossum@...il.com, efault@....de,
	jeremy@...p.org, npiggin@...e.de, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain
	support to use NMI-safe methods


* Avi Kivity <avi@...hat.com> wrote:

> On 06/15/2009 09:55 PM, H. Peter Anvin wrote:
>> Ingo Molnar wrote:
>>    
>>>> I wouldn't actually expect that, *as long as* there is
>>>> serialization between the cr2 write and the cr2 read.
>>>>        
>>> Well, is there any OS that heavily relies on cr2 writes and which
>>> uses them from NMI context, and which CPU makers care about?
>>> (Meaning: Windows, pretty much.)
>>>
>>> If not then i agree that in theory it should work fine, but in
>>> practice we only know that we dont know the unknown risk here ;-)
>>>
>>>      
>>
>> I think you can drop "uses them from NMI context" from that statement;
>> writing to %cr2 is independent of the context.
>>
>> I can try to find out internally what Intel's position on writing 
>> %cr2 is, but it'll take a while; however, KVM should be able to 
>> tell you if any random OS uses %cr2 writes (as should a static 
>> disassembly of their kernel.)
>
> Linux is one such OS.  When acting as a hypervisor it writes cr2 
> to present its guests with their expected environment (any 
> hypervisor that uses virtualization extensions will of course need 
> to do this).

Ah, it does save/restore it in svm_vcpu_run. VMX can do this via its 
context structure (without explicit CR manipulations in host space), 
right?

	Ingo
--
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/