KVM: fix the handling of dirty bitmaps to avoid overflows

(Cherry-picked from commit 87bf6e7d)

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

arch/ia64/kvm/kvm-ia64.c

@@ -1797,7 +1797,8 @@ static int kvm_ia64_sync_dirty_log(struct kvm *kvm,
 {
 	struct kvm_memory_slot *memslot;
 	int r, i;
-	long n, base;
+	long base;
+	unsigned long n;
 	unsigned long *dirty_bitmap = (unsigned long *)(kvm->arch.vm_base +
 			offsetof(struct kvm_vm_data, kvm_mem_dirty_log));
 
@@ -1810,7 +1811,7 @@ static int kvm_ia64_sync_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);
 	base = memslot->base_gfn / BITS_PER_LONG;
 
 	for (i = 0; i < n/sizeof(long); ++i) {
@@ -1826,7 +1827,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 		struct kvm_dirty_log *log)
 {
 	int r;
-	int n;
+	unsigned long n;
 	struct kvm_memory_slot *memslot;
 	int is_dirty = 0;
 
@@ -1844,7 +1845,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 	if (is_dirty) {
 		kvm_flush_remote_tlbs(kvm);
 		memslot = &kvm->memslots[log->slot];
-		n = ALIGN(memslot->npages, BITS_PER_LONG) / 8;
+		n = kvm_dirty_bitmap_bytes(memslot);
 		memset(memslot->dirty_bitmap, 0, n);
 	}
 	r = 0;

arch/x86/kvm/x86.c

@@ -2133,7 +2133,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 				      struct kvm_dirty_log *log)
 {
 	int r;
-	int n;
+	unsigned long n;
 	struct kvm_memory_slot *memslot;
 	int is_dirty = 0;
 
@@ -2149,7 +2149,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 		kvm_mmu_slot_remove_write_access(kvm, log->slot);
 		spin_unlock(&kvm->mmu_lock);
 		memslot = &kvm->memslots[log->slot];
-		n = ALIGN(memslot->npages, BITS_PER_LONG) / 8;
+		n = kvm_dirty_bitmap_bytes(memslot);
 		memset(memslot->dirty_bitmap, 0, n);
 	}
 	r = 0;

include/linux/kvm_host.h

@@ -116,6 +116,11 @@ struct kvm_memory_slot {
 	int user_alloc;
 };
 
+static inline unsigned long kvm_dirty_bitmap_bytes(struct kvm_memory_slot *memslot)
+{
+	return ALIGN(memslot->npages, BITS_PER_LONG) / 8;
+}
+
 struct kvm_kernel_irq_routing_entry {
 	u32 gsi;
 	u32 type;

virt/kvm/kvm_main.c

@@ -1226,7 +1226,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
 	/* 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)
@@ -1309,7 +1309,7 @@ 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;
@@ -1321,7 +1321,7 @@ 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];
@@ -1663,10 +1663,13 @@ 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 (!test_bit(rel_gfn, memslot->dirty_bitmap))
-			set_bit(rel_gfn, memslot->dirty_bitmap);
+		if (!test_bit(offset, p))
+			set_bit(offset, p);
 	}
 }