kernel-hardening - Re: [PATCH 04/13] mm: Track NR_KERNEL_STACK in pages instead of number of stacks

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Message-ID: <CALCETrXRONH1K1zAWAFN--Lsza+5bkgtmcMrgAY_nvT-e21C3w@mail.gmail.com>
Date: Thu, 16 Jun 2016 10:39:43 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>, 
	Borislav Petkov <bp@...en8.de>, Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>, 
	Brian Gerst <brgerst@...il.com>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Vladimir Davydov <vdavydov@...tuozzo.com>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 04/13] mm: Track NR_KERNEL_STACK in pages instead of
 number of stacks

On Thu, Jun 16, 2016 at 8:33 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> On Wed, Jun 15, 2016 at 05:28:26PM -0700, Andy Lutomirski wrote:
>> Currently, NR_KERNEL_STACK tracks the number of kernel stacks in a
>> zone.  This only makes sense if each kernel stack exists entirely in
>> one zone, and allowing vmapped stacks could break this assumption.
>>
>> It turns out that the code for tracking kernel stack allocations in
>> units of pages is slightly simpler, so just switch to counting
>> pages.
>>
>> Cc: Vladimir Davydov <vdavydov@...tuozzo.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: Michal Hocko <mhocko@...nel.org>
>> Cc: linux-mm@...ck.org
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> ---
>>  fs/proc/meminfo.c | 2 +-
>>  kernel/fork.c     | 3 ++-
>>  mm/page_alloc.c   | 3 +--
>>  3 files changed, 4 insertions(+), 4 deletions(-)
>
> You missed another usage of NR_KERNEL_STACK in drivers/base/node.c.

Thanks.

The real reason I cc'd you was so you could look at
rewind_stack_do_exit and the sneaky trick I did in no_context in the
last patch, though.  :)  Both survive objtool, but I figured I'd check
with objtool's author as well.  If there was a taint bit I could set
saying "kernel is hosed -- don't try to apply live patches any more",
I'd have extra confidence.

--Andy

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