[PATCH] KVM: fix the handling of dirty bitmaps to avoid overflows

This patch fixes a bug found by Avi during the review process
of my dirty bitmap related work.

To ppc and ia64 people:
  The fix is really simple but touches all architectures using
  dirty bitmaps. So please check this will not suffer your part.

=
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 <[email protected]>
---
 arch/ia64/kvm/kvm-ia64.c  |    9 +++++----
 arch/powerpc/kvm/book3s.c |    5 +++--
 arch/x86/kvm/x86.c        |    5 +++--
 include/linux/kvm_host.h  |    5 +++++
 virt/kvm/kvm_main.c       |   13 ++++++++-----
 5 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index b0ed80c..566aff6 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -1806,7 +1806,8 @@ 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));
 
@@ -1819,7 +1820,7 @@ 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) {
@@ -1835,7 +1836,7 @@ 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;
 
@@ -1854,7 +1855,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 	if (is_dirty) {
 		kvm_flush_remote_tlbs(kvm);
 		memslot = &kvm->memslots->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;
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index a7ab2ea..4ac7b15 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -1118,7 +1118,8 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 	struct kvm_vcpu *vcpu;
 	ulong ga, ga_end;
 	int is_dirty = 0;
-	int r, n;
+	int r;
+	unsigned long n;
 
 	mutex_lock(&kvm->slots_lock);
 
@@ -1136,7 +1137,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 		kvm_for_each_vcpu(n, vcpu, kvm)
 			kvmppc_mmu_pte_pflush(vcpu, ga, ga_end);
 
-		n = ALIGN(memslot->npages, BITS_PER_LONG) / 8;
+		n = kvm_dirty_bitmap_bytes(memslot);
 		memset(memslot->dirty_bitmap, 0, n);
 	}
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fd5c3d3..bb36c3c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2648,8 +2648,9 @@ static int kvm_vm_ioctl_reinject(struct kvm *kvm,
 int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 				      struct kvm_dirty_log *log)
 {
-	int r, n, i;
+	int r, i;
 	struct kvm_memory_slot *memslot;
+	unsigned long n;
 	unsigned long is_dirty = 0;
 	unsigned long *dirty_bitmap = NULL;
 
@@ -2664,7 +2665,7 @@ int kvm_vm_ioctl_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);
 
 	r = -ENOMEM;
 	dirty_bitmap = vmalloc(n);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8e91fa7..169d077 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -119,6 +119,11 @@ 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;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 9379533..6fe79c4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -645,7 +645,7 @@ 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)
@@ -765,7 +765,7 @@ 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;
@@ -777,7 +777,7 @@ 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];
@@ -1183,10 +1183,13 @@ 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);
 	}
 }
 
-- 
1.6.3.3