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

crypto: ccp - Do not initialize SNP for ioctl(SNP_VLEK_LOAD)

Sashiko notes:

> if SEV initialization fails and KVM is actively running normal VMs, could a
> userspace process trigger this code path via /dev/sev ioctls (e.g.,
> SEV_PDH_GEN) and zero out MSR_VM_HSAVE_PA globally? Would the next VMRUN
> execution for an active VM trigger a general protection fault and crash the
> host?

The SEV firmware docs for SNP_VLEK_LOAD note:

> On SNP_SHUTDOWN, the VLEK is deleted.

That is, the initialization/shutdown wrapper here is pointless, because the
firmware immediately throws away the key anyway. Instead, refuse to do
anything if SNP has not been previously initialized.

This is an ABI break: before, this was a no-op and almost certainly a
mistake by userspace, and now it returns -ENODEV. ABI compatibility could be
maintained here by simply returning 0 in the check instead.

https://git.kernel.org/stable/c/61cf5eef20657bff9ca235fe938a99ce5ff65c06

https://git.kernel.org/stable/c/8836801847b9479ac046cb18a24981e1b0b05e9d

https://git.kernel.org/stable/c/92567ed9306d5a3d1b007eb4faeff30cc3ffc3e4

https://git.kernel.org/stable/c/f91e9dbb5845d1e5abf1028e6df57dcf61583e1b

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