CVE-2020-11739

Official description

An issue was discovered in Xen through 4.13.x, allowing guest OS users to cause a denial of service or possibly gain privileges because of missing memory barriers in read-write unlock paths. The read-write unlock paths don't contain a memory barrier. On Arm, this means a processor is allowed to re-order the memory access with the preceding ones. In other words, the unlock may be seen by another processor before all the memory accesses within the "critical" section. As a consequence, it may be possible to have a writer executing a critical section at the same time as readers or another writer. In other words, many of the assumptions (e.g., a variable cannot be modified after a check) in the critical sections are not safe anymore. The read-write locks are used in hypercalls (such as grant-table ones), so a malicious guest could exploit the race. For instance, there is a small window where Xen can leak memory if XENMAPSPACE_grant_table is used concurrently. A malicious guest may be able to leak memory, or cause a hypervisor crash resulting in a Denial of Service (DoS). Information leak and privilege escalation cannot be excluded.

Affected packages & fixed versions

Affected products (as reported)

References

• https://xenbits.xen.org/xsa/advisory-314.html x_refsource_MISC
• http://xenbits.xen.org/xsa/advisory-314.html x_refsource_CONFIRM
• [oss-security] 20200414 Xen Security Advisory 314 v3 (CVE-2020-11739) - Missing memory barriers in read-write unlock paths mailing-list, x_refsource_MLIST
• FEDORA-2020-440457afe4 vendor-advisory, x_refsource_FEDORA
• FEDORA-2020-295ed0b1e0 vendor-advisory, x_refsource_FEDORA
• openSUSE-SU-2020:0599 vendor-advisory, x_refsource_SUSE
• FEDORA-2020-cbc3149753 vendor-advisory, x_refsource_FEDORA
• GLSA-202005-08 vendor-advisory, x_refsource_GENTOO
• DSA-4723 vendor-advisory, x_refsource_DEBIAN