linux-kernel - Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in die

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:	Thu, 7 Feb 2008 15:37:37 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>, Vivek Goyal <vgoyal@...hat.com>,
	tglx@...utronix.de, mingo@...hat.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in
	die_nmi path

On Thu, Feb 07, 2008 at 01:24:04PM +0100, Ingo Molnar wrote:
> 
> * Neil Horman <nhorman@...driver.com> wrote:
> 
> > Ingo noted a few posts down the nmi_exit doesn't actually write to the 
> > APIC EOI register, so yeah, I agree, its bogus (and I apologize, I 
> > should have checked that more carefully).  Nevertheless, this patch 
> > consistently allowed a hangning machine to boot through an Nmi lockup.  
> > So I'm forced to wonder whats going on then that this patch helps 
> > with.  perhaps its a just a very fragile timing issue, I'll need to 
> > look more closely.
> 
> try a dummy iret, something like:
> 
>   asm volatile ("pushf; push $1f; iret; 1: \n");
> 
> to get the CPU out of its 'nested NMI' state. (totally untested)
> 
> the idea is to push down an iret frame to the kernel stack that will 
> just jump to the next instruction and gets it out of the NMI nesting. 
> Note: interrupts will/must still be disabled, despite the iret. (the 
> ordering of the pushes might be wrong, we might need more than that for 
> a valid iret, etc. etc.)
> 
> 	Ingo

Will do.  I'll report results as soon as I have them,.  Thanks!
Neil

-- 
/****************************************************
 * Neil Horman <nhorman@...driver.com>
 * Software Engineer, Red Hat
 ****************************************************/
--
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/