On Wed, Sep 21, 2022, Aaron Lewis wrote: > Protect the kernel from using the flag KVM_MSR_FILTER_DEFAULT_ALLOW. > Its value is 0, and using it incorrectly could have unintended > consequences. E.g. prevent someone in the kernel from writing something > like this. > > if (filter.flags & KVM_MSR_FILTER_DEFAULT_ALLOW) > <allow the MSR> > > and getting confused when it doesn't work. > > It would be more ideal to remove this flag altogether, but userspace > may already be using it, so protecting the kernel is all that can > reasonably be done at this point. > > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Signed-off-by: Aaron Lewis <aaronlewis@xxxxxxxxxx> > --- Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Google's VMM is already using this flag, so we *know* that dropping the > flag entirely will break userspace. All we can do at this point is > prevent the kernel from using it. LOL, nice.
