On Mon, Jan 15, 2024, Paul Durrant wrote:
> @@ -638,20 +637,32 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct
> kvm_xen_hvm_attr *data)
> }
> break;
>
> - case KVM_XEN_ATTR_TYPE_SHARED_INFO: {
> + case KVM_XEN_ATTR_TYPE_SHARED_INFO:
> + case KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA: {
> int idx;
>
> mutex_lock(&kvm->arch.xen.xen_lock);
>
> idx = srcu_read_lock(&kvm->srcu);
>
> - if (data->u.shared_info.gfn == KVM_XEN_INVALID_GFN) {
> - kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
> - r = 0;
> + if (data->type == KVM_XEN_ATTR_TYPE_SHARED_INFO) {
> + if (data->u.shared_info.gfn == KVM_XEN_INVALID_GFN) {
> + kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
> + r = 0;
> + } else {
> + r =
> kvm_gpc_activate(&kvm->arch.xen.shinfo_cache,
> +
> gfn_to_gpa(data->u.shared_info.gfn),
> + PAGE_SIZE);
> + }
> } else {
> - r = kvm_gpc_activate(&kvm->arch.xen.shinfo_cache,
> -
> gfn_to_gpa(data->u.shared_info.gfn),
> - PAGE_SIZE);
> + if (data->u.shared_info.hva == 0) {
I know I said I don't care about the KVM Xen ABI, but I still think using '0' as
"invalid" is ridiculous.
More importantly, this code needs to check that HVA is a userspace pointer.
Because __kvm_set_memory_region() performs the address checks, KVM assumes any
hva that it gets out of a memslot, i.e. from a gfn, is a safe userspace address.
kvm_is_error_hva() will catch most addresses, but I'm pretty sure there's still
a small window where userspace could use this to write kernel memory.
> + kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
> + r = 0;
> + } else {
> + r =
> kvm_gpc_activate_hva(&kvm->arch.xen.shinfo_cache,
> +
> data->u.shared_info.hva,
> + PAGE_SIZE);
> + }
