kvm: x86: fix KVM_XEN_HVM_CONFIG ioctl

This ioctl is obsolete (it was used by Xenner as far as I know) but
still let's not break it gratuitously...  Its handler is copying
directly into struct kvm.  Go through a bounce buffer instead, with
the added benefit that we can actually do something useful with the
flags argument---the previous code was exiting with -EINVAL but still
doing the copy.

This technically is a userspace ABI breakage, but since no one should be
using the ioctl, it's a good occasion to see if someone actually
complains.

Cc: kernel-hardening@lists.openwall.com
Cc: Kees Cook <keescook@chromium.org>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index eee8e7faf1af5778763b8181df472651d3573149..6c16461e3a86195db25026b6d1da128af8d78a55 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4238,13 +4238,14 @@ set_identity_unlock:
                mutex_unlock(&kvm->lock);
                break;
        case KVM_XEN_HVM_CONFIG: {
+               struct kvm_xen_hvm_config xhc;
                r = -EFAULT;
-               if (copy_from_user(&kvm->arch.xen_hvm_config, argp,
-                                  sizeof(struct kvm_xen_hvm_config)))
+               if (copy_from_user(&xhc, argp, sizeof(xhc)))
                        goto out;
                r = -EINVAL;
-               if (kvm->arch.xen_hvm_config.flags)
+               if (xhc.flags)
                        goto out;
+               memcpy(&kvm->arch.xen_hvm_config, &xhc, sizeof(xhc));
                r = 0;
                break;
        }