linux-kernel - Re: [PATCH] virt: acrn: Prefer array_syze and struct

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Date:   Tue, 12 Oct 2021 09:34:29 +0800
From:   Li Fei1 <fei1.li@...el.com>
To:     Len Baker <len.baker@....com>
Cc:     keescook@...omium.org, gustavoars@...nel.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        fei1.li@...el.com
Subject: Re: [PATCH] virt: acrn: Prefer array_syze and struct_size over open
 coded arithmetic

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@....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@...el.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
>