On Wed, Jun 12, 2019 at 07:08:24PM +0200, Marius Hillenbrand wrote: > The Linux kernel has a global address space that is the same for any > kernel code. This address space becomes a liability in a world with > processor information leak vulnerabilities, such as L1TF. With the right > cache load gadget, an attacker-controlled hyperthread pair can leak > arbitrary data via L1TF. Disabling hyperthreading is one recommended > mitigation, but it comes with a large performance hit for a wide range > of workloads. > > An alternative mitigation is to not make certain data in the kernel > globally visible, but only when the kernel executes in the context of > the process where this data belongs to. > > This patch series proposes to introduce a region for what we call > process-local memory into the kernel's virtual address space. Page > tables and mappings in that region will be exclusive to one address > space, instead of implicitly shared between all kernel address spaces. > Any data placed in that region will be out of reach of cache load > gadgets that execute in different address spaces. To implement > process-local memory, we introduce a new interface kmalloc_proclocal() / > kfree_proclocal() that allocates and maps pages exclusively into the > current kernel address space. As a first use case, we move architectural > state of guest CPUs in KVM out of reach of other kernel address spaces. Can you briefly describe what types of attacks this is intended to mitigate? E.g. guest-guest, userspace-guest, etc... I don't want to make comments based on my potentially bad assumptions. > The patch set is a prototype for x86-64 that we have developed on top of > kernel 4.20.17 (with cherry-picked commit d253ca0c3865 "x86/mm/cpa: Add > set_direct_map_*() functions"). I am aware that the integration with KVM > will see some changes while rebasing to 5.x. Patches 7 and 8, in Ha, "some" :-) > particular, help make patch 9 more readable, but will be dropped in > rebasing. We have tested the code on both Intel and AMDs, launching VMs > in a loop. So far, we have not done in-depth performance evaluation. > Impact on starting VMs was within measurement noise.
