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From: Kees Cook <keescook@chromium.org>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Andy Lutomirski <luto@kernel.org>,
	Hoeun Ryu <hoeun.ryu@gmail.com>, PaX Team <pageexec@freemail.hu>,
	Emese Revfy <re.emese@gmail.com>,
	"x86@kernel.org" <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC v2] Introduce rare_write() infrastructure
Date: Wed, 29 Mar 2017 12:14:45 -0700
Message-ID: <CAGXu5j+v2kc60x9q2nmeygrxmLCrqoCEh5Tx7U8NyZo7E2BeYA@mail.gmail.com> (raw)
In-Reply-To: <20170329190008.GE7909@n2100.armlinux.org.uk>

On Wed, Mar 29, 2017 at 12:00 PM, Russell King - ARM Linux
<linux@armlinux.org.uk> wrote:
> On Wed, Mar 29, 2017 at 11:15:52AM -0700, Kees Cook wrote:
>> This is take 2 of an RFC series to demonstrate a possible infrastructure
>> for the "write rarely" memory storage type in the kernel (patch 1). The
>> intent is to further reduce the internal attack surface of the kernel
>> by making more variables read-only while "at rest". This is heavily
>> based on the "__read_only" portion of the KERNEXEC infrastructure from
>> PaX/grsecurity, though I tried to adjust it to be more in line with
>> the upstream discussions around the APIs.
>
> How much data are we talking about here?

The goal is to put as much sensitive stuff from .data as possible into
.rodata, which is mostly structures with function pointers, etc. I
haven't measured the "final" results, since there's still a lot of
work to do to get all the other annotations into upstream.

>> As part of the series I've included both x86 support (patch 4), exactly
>> as done in PaX, and ARM support (patches 5-7), similar to what is done in
>> grsecurity but without support for earlier ARM CPUs. Both are lightly
>> tested by me, though they need a bit more work, especially ARM as it is
>> missing the correct domain marking for kernel modules.
>
> The implementation as it stands on ARM is going to gobble up
> multiples of 1MB of RAM as you need it to be section aligned due to
> using domains, so if we're talking about a small amount of data,
> this is very inefficient.  That also only works for non-LPAE as LPAE
> is unable to use that method.

AIUI, we're just flipping toe domain from DOMAIN_KERNEL to
DOMAIN_WR_RARE on the .rodata section (which is already 1MB aligned),
and (in the future if I or someone else can figure out how) on the
kernel module vmap area (which also shouldn't be changing alignment at
all).

-Kees

-- 
Kees Cook
Pixel Security

      reply index

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-29 18:15 Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 01/11] " Kees Cook
2017-03-29 18:23   ` Kees Cook
2017-03-30  7:44     ` Ho-Eun Ryu
2017-03-30 17:02       ` Kees Cook
2017-04-07  8:09   ` Ho-Eun Ryu
2017-04-07 20:38     ` Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 02/11] lkdtm: add test for " Kees Cook
2017-03-30  9:34   ` [kernel-hardening] " Ian Campbell
2017-03-30 16:16     ` Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 03/11] net: switch sock_diag handlers to rare_write() Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook
2017-03-29 22:38   ` Andy Lutomirski
2017-03-30  1:41     ` Kees Cook
2017-04-05 23:57       ` Andy Lutomirski
2017-04-06  0:14         ` Kees Cook
2017-04-06 15:59           ` Andy Lutomirski
2017-04-07  8:34             ` [kernel-hardening] " Mathias Krause
2017-04-07  9:46               ` Thomas Gleixner
2017-04-07 10:51                 ` Mathias Krause
2017-04-07 13:14                   ` Thomas Gleixner
2017-04-07 13:30                     ` Mathias Krause
2017-04-07 16:14                       ` Andy Lutomirski
2017-04-07 16:22                         ` Mark Rutland
2017-04-07 19:58                         ` PaX Team
2017-04-08  4:58                           ` Andy Lutomirski
2017-04-09 12:47                             ` PaX Team
2017-04-10  0:10                               ` Andy Lutomirski
2017-04-10 10:42                                 ` PaX Team
2017-04-10 16:01                                   ` Andy Lutomirski
2017-04-07 20:44                         ` Thomas Gleixner
2017-04-07 21:20                           ` Kees Cook
2017-04-08  4:12                             ` Daniel Micay
2017-04-08  4:13                               ` Daniel Micay
2017-04-08  4:21                         ` Daniel Micay
2017-04-08  5:07                           ` Andy Lutomirski
2017-04-08  7:33                             ` Daniel Micay
2017-04-08 15:20                               ` Andy Lutomirski
2017-04-09 10:53                                 ` Ingo Molnar
2017-04-10 10:22                                 ` Mark Rutland
2017-04-09 20:24                             ` PaX Team
2017-04-10  0:31                               ` Andy Lutomirski
2017-04-10 19:47                                 ` PaX Team
2017-04-10 20:27                                   ` Andy Lutomirski
2017-04-10 20:13                               ` Kees Cook
2017-04-10 20:17                                 ` Andy Lutomirski
2017-04-07 19:25                       ` Thomas Gleixner
2017-04-07 14:45                   ` Peter Zijlstra
2017-04-10 10:29                     ` Mark Rutland
2017-04-07 19:52                 ` PaX Team
2017-04-10  8:26                   ` Thomas Gleixner
2017-04-10 19:55                     ` PaX Team
2017-04-07  9:37   ` Peter Zijlstra
2017-03-29 18:15 ` [RFC v2][PATCH 05/11] ARM: mm: dump: Add domain to output Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 06/11] ARM: domains: Extract common USER domain init Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 07/11] ARM: mm: set DOMAIN_WR_RARE for rodata Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 08/11] ARM: Implement __arch_rare_write_begin/end() Kees Cook
2017-04-07  9:36   ` Peter Zijlstra
2017-03-29 18:16 ` [RFC v2][PATCH 09/11] list: add rare_write() list helpers Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 10/11] gcc-plugins: Add constify plugin Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 11/11] cgroups: force all struct cftype const Kees Cook
2017-03-29 19:00 ` [RFC v2] Introduce rare_write() infrastructure Russell King - ARM Linux
2017-03-29 19:14   ` Kees Cook [this message]

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