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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