A Linux kernel security update has been released for Ubuntu Linux 20.04 LTS.

USN-5072-1: Linux kernel vulnerabilities

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Ubuntu Security Notice USN-5072-1
September 08, 2021

linux-azure-5.8, linux-oem-5.10 vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.04 LTS

Summary:

Several security issues were fixed in the Linux kernel.

Software Description:
- linux-azure-5.8: Linux kernel for Microsoft Azure cloud systems
- linux-oem-5.10: Linux kernel for OEM systems

Details:

Maxim Levitsky and Paolo Bonzini discovered that the KVM hypervisor
implementation for AMD processors in the Linux kernel allowed a guest VM to
disable restrictions on VMLOAD/VMSAVE in a nested guest. An attacker in a
guest VM could use this to read or write portions of the host's physical
memory. (CVE-2021-3656)

Maxim Levitsky discovered that the KVM hypervisor implementation for AMD
processors in the Linux kernel did not properly prevent a guest VM from
enabling AVIC in nested guest VMs. An attacker in a guest VM could use this
to write to portions of the host's physical memory. (CVE-2021-3653)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.04 LTS:
linux-image-5.10.0-1045-oem 5.10.0-1045.47
linux-image-5.8.0-1041-azure 5.8.0-1041.44~20.04.1
linux-image-azure 5.8.0.1041.44~20.04.13
linux-image-oem-20.04 5.10.0.1045.47
linux-image-oem-20.04b 5.10.0.1045.47

After a standard system update you need to reboot your computer to make
all the necessary changes.

ATTENTION: Due to an unavoidable ABI change the kernel updates have
been given a new version number, which requires you to recompile and
reinstall all third party kernel modules you might have installed.
Unless you manually uninstalled the standard kernel metapackages
(e.g. linux-generic, linux-generic-lts-RELEASE, linux-virtual,
linux-powerpc), a standard system upgrade will automatically perform
this as well.

References:
  https://ubuntu.com/security/notices/USN-5072-1
CVE-2021-3653, CVE-2021-3656

Package Information:
  https://launchpad.net/ubuntu/+source/linux-azure-5.8/5.8.0-1041.44~20.04.1
  https://launchpad.net/ubuntu/+source/linux-oem-5.10/5.10.0-1045.47