CVE-2021-29657

arch/x86/kvm/svm/nested.c in the Linux kernel before 5.11.12 has a use-after-free in which an AMD KVM guest can bypass access control on host OS MSRs when there are nested guests, aka CID-a58d9166a756. This occurs because of a TOCTOU race condition associated with a VMCB12 double fetch in nested_svm_vmrun.

Weakness

The product checks the state of a resource before using that resource, but the resource’s state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state.

Affected Software

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/27.html
• https://cwe.mitre.org/data/definitions/29.html

References

• http://packetstormsecurity.com/files/163324/KVM-nested_svm_vmrun-Double-Fetch.html
• https://bugs.chromium.org/p/project-zero/issues/detail?id=2177
• https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.12
• https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a58d9166a756a0f4a6618e4f593232593d6df134
• https://security.netapp.com/advisory/ntap-20210902-0008/