Re: [PATCH] virt: acrn: Prefer array_syze and struct_size over open coded arithmetic

Li Fei1
2021-10-12T01:34:06Z

On Mon, Oct 11, 2021 at 12:39:02PM +0200, Len Baker wrote:
> 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-arguments
>
> Signed-off-by: Len Baker <len.baker@gmx.com>

Hi Baker

Thanks for helping us to fix this issue. This patch looks good to me.
Please add Signed-off-by: Fei Li <fei1.li@intel.com>.
Only two minor comments.

> ---
> drivers/virt/acrn/acrn_drv.h | 10 ++++++----
> drivers/virt/acrn/mm.c | 9 ++++-----
> 2 files changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/virt/acrn/acrn_drv.h b/drivers/virt/acrn/acrn_drv.h
> index 1be54efa666c..fcc2e3e5232a 100644
> --- a/drivers/virt/acrn/acrn_drv.h
> +++ b/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.
One Tab please.
> *
> * 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
> @@ -55,10 +56,11 @@ struct vm_memory_region_op {
> * ACRN Hypervisor.
> */
> struct vm_memory_region_batch {
> - u16 vmid;
> - u16 reserved[3];
> - u32 regions_num;
> - u64 regions_gpa;
> + u16 vmid;
> + u16 reserved[3];
> + u32 regions_num;
> + u64 regions_gpa;
> + struct vm_memory_region_op regions_op[];
Please use Whitespace instead of Tab.
> };
>
> /**
> diff --git a/drivers/virt/acrn/mm.c b/drivers/virt/acrn/mm.c
> index c4f2e15c8a2b..a881742cd48d 100644
> --- a/drivers/virt/acrn/mm.c
> +++ b/drivers/virt/acrn/mm.c
> @@ -168,7 +168,7 @@ 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(struct page *)));
> if (!pages)
> return -ENOMEM;
>
> @@ -220,16 +220,15 @@ 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);
> --
> 2.25.1
>