CVE-2020-11739

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.

Weakness classification

• nvd@nist.gov: CWE-362

Primary references

• cve@mitre.org — Mailing List, Third Party Advisory
• cve@mitre.org — Mailing List, Patch, Third Party Advisory
• cve@mitre.org — Patch, Vendor Advisory
• cve@mitre.org
• cve@mitre.org
• cve@mitre.org
• cve@mitre.org — Third Party Advisory
• cve@mitre.org — Third Party Advisory
• cve@mitre.org — Patch, Vendor Advisory
• af854a3a-2127-422b-91ae-364da2661108 — Mailing List, Third Party Advisory
• af854a3a-2127-422b-91ae-364da2661108 — Mailing List, Patch, Third Party Advisory
• af854a3a-2127-422b-91ae-364da2661108 — Patch, Vendor Advisory