CVE-2021-28689
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: http://xenbits.xen.org/xsa/advisory-254.html However, IBRS does not architecturally protect ring 0 from predictions learnt in ring 1. For more details, see: https://software.intel.com/security-software-guidance/deep-dives/deep-dive-indirect-branch-restricted-speculation 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.
Notes
Author | Note |
---|---|
mdeslaur | hypervisor packages are in universe. For issues in the hypervisor, add appropriate tags to each section, ex: Tags_xen: universe-binary |
Priority
Status
Package | Release | Status |
---|---|---|
xen Launchpad, Ubuntu, Debian |
impish |
Ignored
(end of life)
|
jammy |
Needs triage
|
|
kinetic |
Ignored
(end of life, was needs-triage)
|
|
bionic |
Needs triage
|
|
focal |
Needs triage
|
|
groovy |
Ignored
(end of life)
|
|
trusty |
Does not exist
|
|
upstream |
Needs triage
|
|
xenial |
Needs triage
|
|
hirsute |
Ignored
(end of life)
|
|
mantic |
Needs triage
|
|
lunar |
Ignored
(end of life, was needs-triage)
|
|
Binaries built from this source package are in Universe and so are supported by the community. |
Severity score breakdown
Parameter | Value |
---|---|
Base score | 5.5 |
Attack vector | Local |
Attack complexity | Low |
Privileges required | Low |
User interaction | None |
Scope | Unchanged |
Confidentiality | High |
Integrity impact | None |
Availability impact | None |
Vector | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N |