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Published: 11 June 2021

x86: Speculative vulnerabilities with bare (non-shim) 32-bit PV guests 32-bit x86 PV guest kernels run in ring 1. At the time when Xen was developed, this area of the i386 architecture was rarely used, which is why Xen was able to use it to implement paravirtualisation, Xen's novel approach to virtualization. In AMD64, Xen had to use a different implementation approach, so Xen does not use ring 1 to support 64-bit guests. With the focus now being on 64-bit systems, and the availability of explicit hardware support for virtualization, fixing speculation issues in ring 1 is not a priority for processor companies. Indirect Branch Restricted Speculation (IBRS) is an architectural x86 extension put together to combat speculative execution sidechannel attacks, including Spectre v2. It was retrofitted in microcode to existing CPUs. For more details on Spectre v2, see: However, IBRS does not architecturally protect ring 0 from predictions learnt in ring 1. For more details, see: Similar situations may exist with other mitigations for other kinds of speculative execution attacks. The situation is quite likely to be similar for speculative execution attacks which have yet to be discovered, disclosed, or mitigated.



CVSS 3 base score: 5.5


Package Release Status
Launchpad, Ubuntu, Debian
bionic Needs triage

focal Needs triage

groovy Ignored
(reached end-of-life)
hirsute Ignored
(reached end-of-life)
impish Needs triage

jammy Needs triage

precise Does not exist

trusty Does not exist

upstream Needs triage

xenial Needs triage


hypervisor packages are in universe. For
issues in the hypervisor, add appropriate
tags to each section, ex:
Tags_xen: universe-binary