[PATCH] virtio_mem: prevent overflow with subblock size

["Michael S. Tsirkin" <mst@redhat.com>]

If subblock size is large (e.g. 1G) 32 bit math involving it
can overflow. Rather than try to catch all instances of that,
let's tweak block size to 64 bit.

It ripples through UAPI which is an ABI change, but it's not too late to
make it, and it will allow supporting >4Gbyte blocks while might
become necessary down the road.

Fixes: 5f1f79bbc9e26 ("virtio-mem: Paravirtualized memory hotplug")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/virtio/virtio_mem.c     | 14 +++++++-------
 include/uapi/linux/virtio_mem.h |  4 ++--
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 2f357142ea5e..7b1bece8a331 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -77,7 +77,7 @@ struct virtio_mem {
 	uint64_t requested_size;
 
 	/* The device block size (for communicating with the device). */
-	uint32_t device_block_size;
+	uint64_t device_block_size;
 	/* The translated node id. NUMA_NO_NODE in case not specified. */
 	int nid;
 	/* Physical start address of the memory region. */
@@ -86,7 +86,7 @@ struct virtio_mem {
 	uint64_t region_size;
 
 	/* The subblock size. */
-	uint32_t subblock_size;
+	uint64_t subblock_size;
 	/* The number of subblocks per memory block. */
 	uint32_t nb_sb_per_mb;
 
@@ -1698,9 +1698,9 @@ static int virtio_mem_init(struct virtio_mem *vm)
 	 * - At least the device block size.
 	 * In the worst case, a single subblock per memory block.
 	 */
-	vm->subblock_size = PAGE_SIZE * 1u << max_t(uint32_t, MAX_ORDER - 1,
-						    pageblock_order);
-	vm->subblock_size = max_t(uint32_t, vm->device_block_size,
+	vm->subblock_size = PAGE_SIZE * 1ul << max_t(uint32_t, MAX_ORDER - 1,
+						     pageblock_order);
+	vm->subblock_size = max_t(uint64_t, vm->device_block_size,
 				  vm->subblock_size);
 	vm->nb_sb_per_mb = memory_block_size_bytes() / vm->subblock_size;
 
@@ -1713,8 +1713,8 @@ static int virtio_mem_init(struct virtio_mem *vm)
 
 	dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr);
 	dev_info(&vm->vdev->dev, "region size: 0x%llx", vm->region_size);
-	dev_info(&vm->vdev->dev, "device block size: 0x%x",
-		 vm->device_block_size);
+	dev_info(&vm->vdev->dev, "device block size: 0x%llx",
+		 (unsigned long long)vm->device_block_size);
 	dev_info(&vm->vdev->dev, "memory block size: 0x%lx",
 		 memory_block_size_bytes());
 	dev_info(&vm->vdev->dev, "subblock size: 0x%x",
diff --git a/include/uapi/linux/virtio_mem.h b/include/uapi/linux/virtio_mem.h
index a455c488a995..a9ffe041843c 100644
--- a/include/uapi/linux/virtio_mem.h
+++ b/include/uapi/linux/virtio_mem.h
@@ -185,10 +185,10 @@ struct virtio_mem_resp {
 
 struct virtio_mem_config {
 	/* Block size and alignment. Cannot change. */
-	__u32 block_size;
+	__u64 block_size;
 	/* Valid with VIRTIO_MEM_F_ACPI_PXM. Cannot change. */
 	__u16 node_id;
-	__u16 padding;
+	__u8 padding[6];
 	/* Start address of the memory region. Cannot change. */
 	__u64 addr;
 	/* Region size (maximum). Cannot change. */
-- 
MST