linux-kernel - Re: [RFC v2] implement SL*B and stack usercopy runtime checks

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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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