CVE-2020-12888 Kernel: vfio: access to disabled MMIO space of some devices may lead to DoS scenario
The VFIO modules allow users (guest VMs) to enable or disable access to the devices' MMIO memory address spaces. If a user attempts to access (read/write) the devices' MMIO address space when it is disabled, some h/w devices issue an interrupt to the CPU to indicate a fatal error condition, crashing the system. This flaw allows a guest user or process to crash the host system resulting in a denial of service.
Patch 1/ is to force the user fault if PFNMAP vma might be DMA mapped before user access.
Patch 2/ setup a vm_ops handler to support dynamic faulting instead of calling remap_pfn_range(). Also provides a list of vmas actively mapping the area which can later use to invalidate those mappings.
Patch 3/ block the user from accessing memory spaces which is disabled by using new vma list support to zap, or invalidate, those memory mappings in order to force them to be faulted back in on access.
Upstreamed patches link: https://lore.kernel.org/kvm/158871401328.15589.17598154478222071285.stgit@gi...
[PATCH v4.19.y 1/3]: Backporting of upsream commit 41311242221e: vfio/type1: Support faulting PFNMAP vmas
[PATCH v4.19.y 2/3]: Backporting of upsream commit 11c4cd07ba11: vfio-pci: Fault mmaps to enable vma tracking
[PATCH v4.19.y 3/3]: Backporting of upsream commit abafbc551fdd: vfio-pci: Invalidate mmaps and block MMIO access on disabled memory