linux-kernel - Re: PANIC: double fault, error_code: 0x0 in 4.0.0-rc3-2, kvm related?

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: <5509DABC.7040401@redhat.com>
Date:	Wed, 18 Mar 2015 21:06:20 +0100
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Stefan Seyfried <stefan.seyfried@...glemail.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Takashi Iwai <tiwai@...e.de>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>
Subject: Re: PANIC: double fault, error_code: 0x0 in 4.0.0-rc3-2, kvm related?

On 03/18/2015 08:26 PM, Andy Lutomirski wrote:
> Hi Linus-
> 
> You seem to enjoy debugging these things.  Want to give this a shot?
> My guess is a vmalloc fault accessing either old_rsp or kernel_stack
> right after swapgs in syscall entry.

The code is:

ENTRY(system_call)
        SWAPGS_UNSAFE_STACK
GLOBAL(system_call_after_swapgs)
        movq    %rsp,PER_CPU_VAR(rsp_scratch)
	movq    PER_CPU_VAR(kernel_stack),%rsp

If PER_CPU_VAR(var) memory access can page fault
(I was thinking this is ensured to never fault),
then on these two instructions such page fault
will be fatal: we will still have userspace %rsp.

I thought we can only get a NMI or debug interrupt here,
and they are both set up to use IST stacks
to prevent this scenario (among other reasons).

-- 
vda
--
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/