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Date: Mon, 18 Jul 2011 14:08:22 -0500
From: Matt Mackall <mpm@...enic.com>
To: Vasiliy Kulikov <segoon@...nwall.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
kernel-hardening@...ts.openwall.com, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
x86@...nel.org, Arnd Bergmann <arnd@...db.de>, Christoph Lameter
<cl@...ux-foundation.org>, Pekka Enberg <penberg@...nel.org>, Andrew Morton
<akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC v2] implement SL*B and stack usercopy runtime checks
On Mon, 2011-07-18 at 22:39 +0400, Vasiliy Kulikov wrote:
> This patch implements 2 additional checks for the data copied from
> kernelspace to userspace and vice versa (original PAX_USERCOPY from PaX
> patch). Currently there are some very simple and cheap comparisons of
> supplied size and the size of a copied object known at the compile time
> in copy_* functions. This patch enhances these checks to check against
> stack frame boundaries and against SL*B object sizes.
>
> More precisely, it checks:
>
> 1) if the data touches the stack, checks whether it fully fits in the stack
> and whether it fully fits in a single stack frame. The latter is arch
> dependent, currently it is implemented for x86 with CONFIG_FRAME_POINTER=y
> only. It limits infoleaks/overwrites to a single frame and local variables
> only, and prevents saved return instruction pointer overwriting.
>
> 2) if the data is from the SL*B cache, checks whether it fully fits in a
> slab page and whether it overflows a slab object. E.g. if the memory
> was allocated as kmalloc(64, GFP_KERNEL) and one tries to copy 150
> bytes, the copy would fail.
FYI, this should almost certainly be split into (at least) two patches:
- the stack check
- the SL*B check (probably one patch per allocator, preceded by one for
any shared infrastructure)
--
Mathematics is the supreme nostalgia of our time.
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