On Thu, Oct 27, 2022, Sean Christopherson wrote: > On Thu, Oct 27, 2022, Paolo Bonzini wrote: > > On 10/13/22 23:12, Sean Christopherson wrote: > > > Always use the size of Xen's non-compat vcpu_runstate_info struct when > > > checking that the GPA+size doesn't cross a page boundary. Conceptually, > > > using the current mode is more correct, but KVM isn't consistent with > > > itself as kvm_xen_vcpu_set_attr() unconditionally uses the "full" size > > > when activating the cache. More importantly, prior to the introduction > > > of the gfn_to_pfn_cache, KVM _always_ used the full size, i.e. allowing > > > the guest (userspace?) to use a poorly aligned GPA in 32-bit mode but not > > > 64-bit mode is more of a bug than a feature, and fixing the bug doesn't > > > break KVM's historical ABI. > > > > I'd rather not introduce additional restrictions in KVM, > > But KVM already has this restriction. "struct vcpu_info" is always checked for > the non-compat size, and as above, "struct vcpu_runstate_info" is checked for the > non-compat size during its initialization. Ah, I forgot those are the same size: BUILD_BUG_ON(sizeof(struct vcpu_info) != sizeof(struct compat_vcpu_info));
