CVE-2021-47389

In the Linux kernel, the following vulnerability has been resolved:

KVM: SVM: fix missing sev_decommission in sev_receive_start

DECOMMISSION the current SEV context if binding an ASID fails after RECEIVE_START. Per AMDs SEV API, RECEIVE_START generates a new guest context and thus needs to be paired with DECOMMISSION:

 The RECEIVE_START command is the only command other than the LAUNCH_START
 command that generates a new guest context and guest handle.

The missing DECOMMISSION can result in subsequent SEV launch failures, as the firmware leaks memory and might not able to allocate more SEV guest contexts in the future.

Note, LAUNCH_START suffered the same bug, but was previously fixed by commit 934002cd660b (KVM: SVM: Call SEV Guest Decommission if ASID binding fails).

Weakness

The product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, languages such as Java, Ruby, and Lisp perform automatic garbage collection that releases memory for objects that have been deallocated.
• Use resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems.
• When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users.
• Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/469.html

References

• https://git.kernel.org/stable/c/efd7866e114dcb44f86d151e843f8276b7efbc67
• https://git.kernel.org/stable/c/f1815e0aa770f2127c5df31eb5c2f0e37b60fa77