Date:	Tue, 17 May 2016 15:32:12 -0400
From:	Kees Cook <keescook@...omium.org>
To:	Thomas Garnier <thgarnie@...gle.com>
Cc:	"H . Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Jonathan Corbet <corbet@....net>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Toshi Kani <toshi.kani@....com>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	Alexander Popov <alpopov@...ecurity.com>,
	Joerg Roedel <jroedel@...e.de>, Dave Young <dyoung@...hat.com>,
	Baoquan He <bhe@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Mark Salter <msalter@...hat.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Greg Thelen <gthelen@...gle.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v5 0/4] x86, boot: KASLR memory randomization

On Tue, May 17, 2016 at 4:15 AM, Kees Cook <keescook@...omium.org> wrote:
> I'm travelling this week, but I'll try to spend some time on it.
>
> -Kees
>
> On Mon, May 16, 2016 at 11:25 AM, Thomas Garnier <thgarnie@...gle.com> wrote:
>> Any feedback on the patch? Ingo? Kees?
>>
>> Kees mentioned he will take care of the build warning on the KASLR
>> refactor (the function is not used right now).
>>
>> Thanks,
>> Thomas
>>
>> On Thu, May 12, 2016 at 12:28 PM, Thomas Garnier <thgarnie@...gle.com> wrote:
>>> This is PATCH v5 for KASLR memory implementation for x86_64.
>>>
>>> Recent changes:
>>>     Add performance information on commit.
>>>     Add details on PUD alignment.
>>>     Add information on testing against the KASLR bypass exploit.
>>>     Rebase on next-20160511 and merge recent KASLR changes.
>>>     Integrate feedback from Kees.
>>>
>>> ***Background:
>>> The current implementation of KASLR randomizes only the base address of
>>> the kernel and its modules. Research was published showing that static
>>> memory can be overwitten to elevate privileges bypassing KASLR.
>>>
>>> In more details:
>>>
>>>    The physical memory mapping holds most allocations from boot and heap
>>>    allocators. Knowning the base address and physical memory size, an
>>>    attacker can deduce the PDE virtual address for the vDSO memory page.
>>>    This attack was demonstrated at CanSecWest 2016, in the "Getting
>>>    Physical Extreme Abuse of Intel Based Paged Systems"
>>>    https://goo.gl/ANpWdV (see second part of the presentation). The
>>>    exploits used against Linux worked successfuly against 4.6+ but fail
>>>    with KASLR memory enabled (https://goo.gl/iTtXMJ). Similar research
>>>    was done at Google leading to this patch proposal. Variants exists to
>>>    overwrite /proc or /sys objects ACLs leading to elevation of privileges.
>>>    These variants were tested against 4.6+.
>>>
>>> This set of patches randomizes base address and padding of three
>>> major memory sections (physical memory mapping, vmalloc & vmemmap).
>>> It mitigates exploits relying on predictable kernel addresses. This
>>> feature can be enabled with the CONFIG_RANDOMIZE_MEMORY option.
>>>
>>> Padding for the memory hotplug support is managed by
>>> CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING. The default value is 10
>>> terabytes.
>>>
>>> The patches were tested on qemu & physical machines. Xen compatibility was
>>> also verified. Multiple reboots were used to verify entropy for each
>>> memory section.
>>>
>>> ***Problems that needed solving:
>>>  - The three target memory sections are never at the same place between
>>>    boots.
>>>  - The physical memory mapping can use a virtual address not aligned on
>>>    the PGD page table.
>>>  - Have good entropy early at boot before get_random_bytes is available.
>>>  - Add optional padding for memory hotplug compatibility.
>>>
>>> ***Parts:
>>>  - The first part prepares for the KASLR memory randomization by
>>>    refactoring entropy functions used by the current implementation and
>>>    support PUD level virtual addresses for physical mapping.
>>>    (Patches 01-02)
>>>  - The second part implements the KASLR memory randomization for all
>>>    sections mentioned.
>>>    (Patch 03)
>>>  - The third part adds support for memory hotplug by adding an option to
>>>    define the padding used between the physical memory mapping section
>>>    and the others.
>>>    (Patch 04)
>>>
>>> Performance data:
>>>
>>> Kernbench shows almost no difference (-+ less than 1%):
>>>
>>> Before:
>>>
>>> Average Optimal load -j 12 Run (std deviation):
>>> Elapsed Time 102.63 (1.2695)
>>> User Time 1034.89 (1.18115)
>>> System Time 87.056 (0.456416)
>>> Percent CPU 1092.9 (13.892)
>>> Context Switches 199805 (3455.33)
>>> Sleeps 97907.8 (900.636)
>>>
>>> After:
>>>
>>> Average Optimal load -j 12 Run (std deviation):
>>> Elapsed Time 102.489 (1.10636)
>>> User Time 1034.86 (1.36053)
>>> System Time 87.764 (0.49345)
>>> Percent CPU 1095 (12.7715)
>>> Context Switches 199036 (4298.1)
>>> Sleeps 97681.6 (1031.11)
>>>
>>> Hackbench shows 0% difference on average (hackbench 90
>>> repeated 10 times):
>>>
>>> attemp,before,after
>>> 1,0.076,0.069
>>> 2,0.072,0.069
>>> 3,0.066,0.066
>>> 4,0.066,0.068
>>> 5,0.066,0.067
>>> 6,0.066,0.069
>>> 7,0.067,0.066
>>> 8,0.063,0.067
>>> 9,0.067,0.065
>>> 10,0.068,0.071
>>> average,0.0677,0.0677
>>>
>>> Thanks!
>>>
>
>
>
> --
> Kees Cook
> Chrome OS & Brillo Security



-- 
Kees Cook
Chrome OS & Brillo Security

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