In the Linux kernel, the following vulnerability has been resolved: crypto: ccp - Do not initialize SNP for ioctl(SNP_CONFIG) Sashiko note

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

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

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?

Refuse to re-try initialization if SNP is not already initialized for
SNP_CONFIG.

This is technically an ABI break: before if SNP initialization failed it
could be transparently retriggered by this ioctl, and if no VMs were
running, everything worked fine. Hopefully this is enough of a corner case
that nobody will notice, but someone does, there are a few options:

• do something like symbol_get() for kvm and refuse to initialize if KVM is
  loaded
• check each cpu's HSAVE_PA for non-zero data before re-initializing
• once initialization has failed, continue to refuse to initialize until
  the ccp module is unloaded