virt: acrn: Prefer array_size and struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the array_size() helper to do the arithmetic instead of the
argument "count * size" in the vzalloc() function.

Also, take the opportunity to add a flexible array member of struct
vm_memory_region_op to the vm_memory_region_batch structure. And then,
change the code accordingly and use the struct_size() helper to do the
arithmetic instead of the argument "size + size * count" in the kzalloc
function.

This code was detected with the help of Coccinelle and audited and fixed
manually.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-argumentsAcked-by: Fei Li <fei1.li@intel.com>
Signed-off-by: Len Baker <len.baker@gmx.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/virt/acrn/acrn_drv.h

@@ -48,6 +48,7 @@ struct vm_memory_region_op {
  * @reserved:		Reserved.
  * @regions_num:	The number of vm_memory_region_op.
  * @regions_gpa:	Physical address of a vm_memory_region_op array.
+ * @regions_op:		Flexible array of vm_memory_region_op.
  *
  * HC_VM_SET_MEMORY_REGIONS uses this structure to manage EPT mappings of
  * multiple memory regions of a User VM. A &struct vm_memory_region_batch
@@ -59,6 +60,7 @@ struct vm_memory_region_batch {
 	u16			   reserved[3];
 	u32			   regions_num;
 	u64			   regions_gpa;
+	struct vm_memory_region_op regions_op[];
 };
 
 /**

drivers/virt/acrn/mm.c

@@ -192,7 +192,7 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
 
 	/* Get the page number of the map region */
 	nr_pages = memmap->len >> PAGE_SHIFT;
-	pages = vzalloc(nr_pages * sizeof(struct page *));
+	pages = vzalloc(array_size(nr_pages, sizeof(*pages)));
 	if (!pages)
 		return -ENOMEM;
 
@@ -244,16 +244,15 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
 	}
 
 	/* Prepare the vm_memory_region_batch */
-	regions_info = kzalloc(sizeof(*regions_info) +
-			       sizeof(*vm_region) * nr_regions,
-			       GFP_KERNEL);
+	regions_info = kzalloc(struct_size(regions_info, regions_op,
+					   nr_regions), GFP_KERNEL);
 	if (!regions_info) {
 		ret = -ENOMEM;
 		goto unmap_kernel_map;
 	}
 
 	/* Fill each vm_memory_region_op */
-	vm_region = (struct vm_memory_region_op *)(regions_info + 1);
+	vm_region = regions_info->regions_op;
 	regions_info->vmid = vm->vmid;
 	regions_info->regions_num = nr_regions;
 	regions_info->regions_gpa = virt_to_phys(vm_region);