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Date: Fri, 24 Jun 2016 10:47:04 -0700
From: Andy Lutomirski <>
To: Linus Torvalds <>
Cc: Brian Gerst <>, Peter Zijlstra <>, 
	Oleg Nesterov <>, Andy Lutomirski <>, 
	"the arch/x86 maintainers" <>, Linux Kernel Mailing List <>, 
	"" <>, Borislav Petkov <>, 
	Nadav Amit <>, Kees Cook <>, 
	"" <>, Josh Poimboeuf <>, 
	Jann Horn <>, Heiko Carstens <>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

On Fri, Jun 24, 2016 at 10:40 AM, Linus Torvalds
<> wrote:
> On Fri, Jun 24, 2016 at 10:21 AM, Linus Torvalds
> <> wrote:
>> But as mentioned, I must have missed something. There were a number of
>> places where the code used the task_stack_page() and
>> task_thread_info() interchangably, which used to work and is no longer
>> true. There might simply be cases I missed.
> .. and immediately as I wrote that, I went "Duh".
> One place I missed was free_thread_info(), which should now free the
> stack, not the ti pointer. But it does
>         struct page *page = virt_to_page(ti);
> and frees that, which is bogus. It turns out that we do do
>         free_thread_info(tsk->stack);
> which is bogus too, and undoes it, but I think I have a few new places
> to look at..

Try patching in this thing, which cleans up a bunch of that core crap:

It might not apply without the rest of my series, though.

FWIW, your patch is much more lenient than my approach: I was planning
prohibiting architectures from supplying their own struct thread_info
if they put it in task_struct.  To make that work, I have patches to
remove everything but cpu, flags, and task from x86's thread_info
first.  I'm planning on tidying them up and sending them out after the
vmap stack stuff lands in -tip -- I don't want to have big series that
depend on each other flying around by email at the same time, because
everyone will go nuts trying to figure out what applies where.


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