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Date: Tue, 12 Jul 2016 11:03:02 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Dave Hansen <dave.hansen@...el.com>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, X86 ML <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>,
Borislav Petkov <bp@...en8.de>, Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>,
Brian Gerst <brgerst@...il.com>, Linus Torvalds <torvalds@...ux-foundation.org>,
Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jann@...jh.net>,
Heiko Carstens <heiko.carstens@...ibm.com>, Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v5 13/32] x86/mm/64: In
vmalloc_fault(), use CR3 instead of current->active_mm
On Tue, Jul 12, 2016 at 10:51 AM, Dave Hansen <dave.hansen@...el.com> wrote:
> On 07/11/2016 01:53 PM, Andy Lutomirski wrote:
>> If we get a vmalloc fault while current->active_mm->pgd doesn't
>> match CR3, we'll crash without this change. I've seen this failure
>> mode on heavily instrumented kernels with virtually mapped stacks.
>
> When does this happen, btw? Crossing page boundaries on the stack
> between the time we swap mm's and the time we switch stacks?
This can happen for any vmalloc fault between the mm swap and writing
to current or current->active_mm. I hit it when playing with KASAN
during the first clone. (KASAN has other issues, but this was one of
them AFAICT.)
--Andy
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