KVM: fix the handling of dirty bitmaps to avoid overflows

Int is not long enough to store the size of a dirty bitmap.

This patch fixes this problem with the introduction of a wrapper
function to calculate the sizes of dirty bitmaps.

Note: in mark_page_dirty(), we have to consider the fact that
  __set_bit() takes the offset as int, not long.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5a0cd194dce0..364daacafb58 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -648,7 +648,7 @@ skip_lpage:
 
         /* Allocate page dirty bitmap if needed */
         if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) {
-                unsigned dirty_bytes = ALIGN(npages, BITS_PER_LONG) / 8;
+                unsigned long dirty_bytes = kvm_dirty_bitmap_bytes(&new);
 
                 new.dirty_bitmap = vmalloc(dirty_bytes);
                 if (!new.dirty_bitmap)
@@ -768,7 +768,7 @@ int kvm_get_dirty_log(struct kvm *kvm,
 {
         struct kvm_memory_slot *memslot;
         int r, i;
-        int n;
+        unsigned long n;
         unsigned long any = 0;
 
         r = -EINVAL;
@@ -780,7 +780,7 @@ int kvm_get_dirty_log(struct kvm *kvm,
         if (!memslot->dirty_bitmap)
                 goto out;
 
-        n = ALIGN(memslot->npages, BITS_PER_LONG) / 8;
+        n = kvm_dirty_bitmap_bytes(memslot);
 
         for (i = 0; !any && i < n/sizeof(long); ++i)
                 any = memslot->dirty_bitmap[i];
@@ -1186,10 +1186,13 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
         memslot = gfn_to_memslot_unaliased(kvm, gfn);
         if (memslot && memslot->dirty_bitmap) {
                 unsigned long rel_gfn = gfn - memslot->base_gfn;
+                unsigned long *p = memslot->dirty_bitmap +
+                                        rel_gfn / BITS_PER_LONG;
+                int offset = rel_gfn % BITS_PER_LONG;
 
                 /* avoid RMW */
-                if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
-                        generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
+                if (!generic_test_le_bit(offset, p))
+                        generic___set_le_bit(offset, p);
         }
 }