KVM: add missing compat KVM_CLEAR_DIRTY_LOG

The arguments to the KVM_CLEAR_DIRTY_LOG ioctl include a pointer,
therefore it needs a compat ioctl implementation.  Otherwise,
32-bit userspace fails to invoke it on 64-bit kernels; for x86
it might work fine by chance if the padding is zero, but not
on big-endian architectures.

Reported-by: Thomas Sattler
Cc: stable@vger.kernel.org
Fixes: 2a31b9db15 ("kvm: introduce manual dirty log reprotect")
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -4391,6 +4391,16 @@ struct compat_kvm_dirty_log {
 	};
 };
 
+struct compat_kvm_clear_dirty_log {
+	__u32 slot;
+	__u32 num_pages;
+	__u64 first_page;
+	union {
+		compat_uptr_t dirty_bitmap; /* one bit per page */
+		__u64 padding2;
+	};
+};
+
 static long kvm_vm_compat_ioctl(struct file *filp,
 			   unsigned int ioctl, unsigned long arg)
 {
@@ -4400,6 +4410,24 @@ static long kvm_vm_compat_ioctl(struct file *filp,
 	if (kvm->mm != current->mm)
 		return -EIO;
 	switch (ioctl) {
+#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
+	case KVM_CLEAR_DIRTY_LOG: {
+		struct compat_kvm_clear_dirty_log compat_log;
+		struct kvm_clear_dirty_log log;
+
+		if (copy_from_user(&compat_log, (void __user *)arg,
+				   sizeof(compat_log)))
+			return -EFAULT;
+		log.slot	 = compat_log.slot;
+		log.num_pages	 = compat_log.num_pages;
+		log.first_page	 = compat_log.first_page;
+		log.padding2	 = compat_log.padding2;
+		log.dirty_bitmap = compat_ptr(compat_log.dirty_bitmap);
+
+		r = kvm_vm_ioctl_clear_dirty_log(kvm, &log);
+		break;
+	}
+#endif
 	case KVM_GET_DIRTY_LOG: {
 		struct compat_kvm_dirty_log compat_log;
 		struct kvm_dirty_log log;