Any feedback on this patch proposal? Thanks, Thomas
On Mon, Apr 25, 2016 at 9:39 AM, Thomas Garnier <thgar...@google.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! >
