linux-kernel - Re: Sanitize CPU-state when switching from virtual-8086 mode to other task

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, 31 Dec 2013 14:21:06 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	halfdog <me@...fdog.net>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Sanitize CPU-state when switching from virtual-8086 mode to
 other task

On Tue, Dec 31, 2013 at 10:42:47AM -0800, H. Peter Anvin wrote:
> On 12/30/2013 07:52 AM, halfdog wrote:
> >>
> >> Still in VirtualBox?
> > 
> > Yes, again: after comparing the results from initrd on real hardware
> > with Vbox, I'm getting to understand the timing problem involved and why
> > timing in VBox is different: The test program usually OOPSes when
> > touching FPU multiple times, otherwise, when terminated before second
> > FPU-interacation, it OOPSes on next invocation, stumbling over invalid
> > CPU state from prior invocation. With improved code, I can rather
> > reliably bring CPU into that state, so that next process invoked and
> > touching FPU/MMX-state is OOPSed. Currently searching SUID-binaries and
> > running UID=0 daemons, that might show interesting reaction on that
> > event, but only on DOS level yet, e.g. after running V2 test program
> > once and then connecting via SSH, this currently kills the ssh daemon
> > nicely.
> > 
> > It seems that machine lockup occurs when e.g. switch to idle task
> > happens at exactly the right moment, which I currently cannot trigger on
> > real hardware, but still working on that.
> > 
> 
> I'm still wondering if this is a VirtualBox-specific problem or if it is
> something that *could* occur on hardware, or in other virtualization
> environments (KVM, Xen HVM, Hy-perV, VMware etc.)

So, I am wondering if this is related to " x86/fpu: CR0.TS should be set before trap
into PV guest's #NM exception handle" which does have a similar pattern - you
do enough of the task switches and the FPU is screwed.

See http://mid.gmane.org/1383720072-6242-1-git-send-email-gaoyang.zyh@taobao.com

(I thought there was a thread about this on LKML too but I can't
find it).
> 
> 	-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/
--
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/