KVM: Enable 32bit dirty log pointers on 64bit host

With big endian userspace, we can't quite figure out if a pointer
is 32 bit (shifted >> 32) or 64 bit when we read a 64 bit pointer.

This is what happens with dirty logging. To get the pointer interpreted
correctly, we thus need Arnd's patch to implement a compat layer for
the ioctl:

A better way to do this is to add a separate compat_ioctl() method that
converts this for you.

Based on initial patch from Arnd Bergmann.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 50 insertions, 1 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index cac69c4415df..bd44fb48ac43 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -43,6 +43,7 @@
 #include <linux/swap.h>
 #include <linux/bitops.h>
 #include <linux/spinlock.h>
+#include <linux/compat.h>
 
 #include <asm/processor.h>
 #include <asm/io.h>
@@ -1542,6 +1543,52 @@ out:
         return r;
 }
 
+#ifdef CONFIG_COMPAT
+struct compat_kvm_dirty_log {
+        __u32 slot;
+        __u32 padding1;
+        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)
+{
+        struct kvm *kvm = filp->private_data;
+        int r;
+
+        if (kvm->mm != current->mm)
+                return -EIO;
+        switch (ioctl) {
+        case KVM_GET_DIRTY_LOG: {
+                struct compat_kvm_dirty_log compat_log;
+                struct kvm_dirty_log log;
+
+                r = -EFAULT;
+                if (copy_from_user(&compat_log, (void __user *)arg,
+                                   sizeof(compat_log)))
+                        goto out;
+                log.slot         = compat_log.slot;
+                log.padding1     = compat_log.padding1;
+                log.padding2     = compat_log.padding2;
+                log.dirty_bitmap = compat_ptr(compat_log.dirty_bitmap);
+
+                r = kvm_vm_ioctl_get_dirty_log(kvm, &log);
+                if (r)
+                        goto out;
+                break;
+        }
+        default:
+                r = kvm_vm_ioctl(filp, ioctl, arg);
+        }
+
+out:
+        return r;
+}
+#endif
+
 static int kvm_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
         struct page *page[1];
@@ -1576,7 +1623,9 @@ static int kvm_vm_mmap(struct file *file, struct vm_area_struct *vma)
 static struct file_operations kvm_vm_fops = {
         .release        = kvm_vm_release,
         .unlocked_ioctl = kvm_vm_ioctl,
-        .compat_ioctl   = kvm_vm_ioctl,
+#ifdef CONFIG_COMPAT
+        .compat_ioctl   = kvm_vm_compat_ioctl,
+#endif
         .mmap           = kvm_vm_mmap,
 };