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Message-ID: <3742830.xcm4l8nxyl@wuerfel>
Date: Tue, 21 Jun 2016 21:44:13 +0200
From: Arnd Bergmann <arnd@...db.de>
To: Rik van Riel <riel@...hat.com>
Cc: kernel-hardening@...ts.openwall.com, Andy Lutomirski <luto@...capital.net>, Jann Horn <jannh@...gle.com>, Andy Lutomirski <luto@...nel.org>, 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>, 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>
Subject: Re: Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support
On Tuesday, June 21, 2016 2:32:28 PM CEST Rik van Riel wrote:
> On Tue, 2016-06-21 at 10:13 -0700, Kees Cook wrote:
> > On Tue, Jun 21, 2016 at 9:59 AM, Andy Lutomirski <luto@...capital.net
> > > wrote:
> > >
> > > I'm tempted to explicitly disallow VM_NO_GUARD in the vmalloc
> > > range.
> > > It has no in-tree users for non-fixed addresses right now.
> > What about the lack of pre-range guard page? That seems like a
> > critical feature for this.
>
> If VM_NO_GUARD is disallowed, and every vmalloc area has
> a guard area behind it, then every subsequent vmalloc area
> will have a guard page ahead of it.
>
> I think disallowing VM_NO_GUARD will be all that is required.
>
> The only thing we may want to verify on the architectures that
> we care about is that there is nothing mapped immediately before
> the start of the vmalloc range, otherwise the first vmalloced
> area will not have a guard page below it.
FWIW, ARM has an 8MB guard area between the linear mapping of
physical memory and the start of the vmalloc area. I have not
checked any of the other architectures though.
Arnd
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