KVM: x86: Re-pend GET_NESTED_STATE_PAGES if getting said pages fails

Overview

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

KVM: x86: Re-pend GET_NESTED_STATE_PAGES if getting said pages fails

Re-pend GET_NESTED_STATE_PAGES before exiting to userspace if getting the nested pages fails in the KVM_RUN path. If userspace re-runs the vCPU, and vmcs02 holds valid PFNs from the previous run of L2, then KVM could re-enter L2 with stale, unpinned PFNs mapped into e.g. the vAPIC page.

Note, both SVM and VMX (as of commit 11722439fb20 ("KVM: nVMX: Ensure KVM_REQ_GET_NESTED_STATE_PAGES is cleared on VM-Exit") ensure the request is cleared on VM-Exit (including the "forced" case), i.e. there is no risk of double-mapping due to emulated VMLAUNCH/VMRESUME/VMRUN and the request trying to map the nested pages.

Affected

• Linux >= 671ddc700fd08b94967b1e2a937020e30c838609 < 525694a6021ec6c8f7ce1f38acdf2dd77698fec1
• Linux >= 671ddc700fd08b94967b1e2a937020e30c838609 < 942192dbcd3a06695ef6b31cf10a41a21cf014d8
• Linux >= 671ddc700fd08b94967b1e2a937020e30c838609 < 10180a277549339020b08000206092c07e0bff5a
• Linux 5.4

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.