Date: Fri, 29 Apr 2016 09:42:53 -0700 From: Thomas Garnier <thgarnie@...gle.com> To: "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>, Thomas Garnier <thgarnie@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, Dan Williams <dan.j.williams@...el.com>, Kees Cook <keescook@...omium.org>, 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> Cc: x86@...nel.org, LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org, Greg Thelen <gthelen@...gle.com>, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH 0/4] x86, boot: KASLR memory randomization Any feedback on this patch proposal? Thanks, Thomas On Mon, Apr 25, 2016 at 9:39 AM, Thomas Garnier <thgarnie@...gle.com> wrote: > This is PATCH v1 for KASLR memory implementation on x86_64. Minor changes > were done based on RFC v1 comments. > > ***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). 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) > > Thanks! >
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