Debian Security Advisory
DLA-1990-1 linux-4.9 -- LTS security update
- Date Reported:
- 13 Nov 2019
- Affected Packages:
- Security database references:
- In Mitre's CVE dictionary: CVE-2018-12207, CVE-2019-0154, CVE-2019-0155, CVE-2019-11135.
- More information:
Several vulnerabilities have been discovered in the Linux kernel that may lead to a privilege escalation, denial of service, or information leak.
It was discovered that on Intel CPUs supporting hardware virtualisation with Extended Page Tables (EPT), a guest VM may manipulate the memory management hardware to cause a Machine Check Error (MCE) and denial of service (hang or crash).
The guest triggers this error by changing page tables without a TLB flush, so that both 4 KB and 2 MB entries for the same virtual address are loaded into the instruction TLB (iTLB). This update implements a mitigation in KVM that prevents guest VMs from loading 2 MB entries into the iTLB. This will reduce performance of guest VMs.
Further information on the mitigation can be found at https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/multihit.html or in the linux-doc-4.9 package.
Intel's explanation of the issue can be found at software.intel.com/…/deep-dive-machine-check-error-avoidance-page-size-change-0.
Intel discovered that on their 8th and 9th generation GPUs, reading certain registers while the GPU is in a low-power state can cause a system hang. A local user permitted to use the GPU can use this for denial of service.
This update mitigates the issue through changes to the i915 driver.
The affected chips (gen8 and gen9) are listed at en.wikipedia.org/wiki/List_of_Intel_graphics_processing_units.
Intel discovered that their 9th generation and newer GPUs are missing a security check in the Blitter Command Streamer (BCS). A local user permitted to use the GPU could use this to access any memory that the GPU has access to, which could result in a denial of service (memory corruption or crash), a leak of sensitive information, or privilege escalation.
This update mitigates the issue by adding the security check to the i915 driver.
The affected chips (gen9 onward) are listed at en.wikipedia.org/wiki/List_of_Intel_graphics_processing_units.
It was discovered that on Intel CPUs supporting transactional memory (TSX), a transaction that is going to be aborted may continue to execute speculatively, reading sensitive data from internal buffers and leaking it through dependent operations. Intel calls this
TSX Asynchronous Abort(TAA).
For CPUs affected by the previously published Microarchitectural Data Sampling (MDS) issues (CVE-2018-12126, CVE-2018-12127, CVE-2018-12130, CVE-2019-11091), the existing mitigation also mitigates this issue.
For processors that are vulnerable to TAA but not MDS, this update disables TSX by default. This mitigation requires updated CPU microcode. An updated intel-microcode package (only available in Debian non-free) will be provided via a future DLA. The updated CPU microcode may also be available as part of a system firmware ("BIOS") update.
Further information on the mitigation can be found at www.kernel.org/…/tsx_async_abort.html or in the linux-doc-4.9 package.
Intel's explanation of the issue can be found at software.intel.com/…/deep-dive-intel-transactional-synchronization-extensions-intel-tsx-asynchronous-abort.
For Debian 8
Jessie, these problems have been fixed in version 4.9.189-3+deb9u2~deb8u1.
We recommend that you upgrade your linux-4.9 packages.
Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: https://wiki.debian.org/LTS