Linux kernel (arch/x86/kvm/svm): Page State Change requests from a confidential guest were validated against the

Impact

Page State Change requests from a confidential guest were validated against the maximum possible scratch-area size rather than the size the guest's own pointer actually leaves available, so a guest can make the host walk PSC entries beyond the buffer. Result is guest-directed out-of-bounds access in host kernel memory from inside an encrypted VM.

Who can reach it

Issued by the guest itself: a SEV-SNP guest places its scratch pointer at a non-zero offset in the GHCB shared buffer and submits a PSC request whose entry indices run past the effective end. No host privilege, no VMM involvement. Conditional on the node running SEV-SNP guests on kvm_amd.

What to do

Boot a kernel with the referenced stable commits applied; the record carries no fixed release string, so verify by commit. Until then, keep SEV-SNP tenants off the affected nodes or downgrade those workloads to non-confidential VMs.

References