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Date: Tue, 12 Jul 2016 11:03:02 -0700
From: Andy Lutomirski <>
To: Dave Hansen <>
Cc: "" <>, X86 ML <>, 
	"" <>, linux-arch <>, 
	Borislav Petkov <>, Nadav Amit <>, Kees Cook <>, 
	Brian Gerst <>, Linus Torvalds <>, 
	Josh Poimboeuf <>, Jann Horn <>, 
	Heiko Carstens <>, Andy Lutomirski <>
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 <> 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.)


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