linux-kernel - Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

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: <5356CE58.1090502@zytor.com>
Date:	Tue, 22 Apr 2014 13:17:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Brian Gerst <brgerst@...il.com>
CC:	Andrew Lutomirski <amluto@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	Alexandre Julliard <julliard@...ehq.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

On 04/22/2014 12:55 PM, Brian Gerst wrote:
> On Tue, Apr 22, 2014 at 2:51 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> On 04/22/2014 11:17 AM, Brian Gerst wrote:
>>>>
>>>> That is the entry condition that we have to deal with.  The fact that
>>>> the switch to the IST is unconditional is what makes ISTs hard to deal with.
>>>
>>> Right, that is why you switch away from the IST as soon as possible,
>>> copying the data that is already pushed there to another stack so it
>>> won't be overwritten by a recursive fault.
>>>
>>
>> That simply will not work if you can take a #GP due to the "safe" MSR
>> functions from NMI and #MC context, which would be my main concern.
> 
> In that case (#2 above), you would switch to the previous %rsp (in the
> NMI/MC stack), copy the exception frame from the IST, and continue
> with the #GP handler.  That effectively is the same as it is today,
> where no stack switch occurs on the #GP fault.
> 

1. You take #GP.  This causes an IST stack switch.
2. You immediately thereafter take an NMI.  This switches stacks again.
3. Now you take another #GP.  This causes another IST stack, and now you
have clobbered your return information, and cannot resume.

	-hpa

--
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/