linux-hardening - Re: [PATCH] virt: acrn: Annotate struct vm_memory_region_batch with __counted

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Date: Sat, 23 Sep 2023 10:32:16 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>, Fei Li <fei1.li@...el.com>
Cc: Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] virt: acrn: Annotate struct vm_memory_region_batch with
 __counted_by



On 9/22/23 11:51, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct vm_memory_region_batch.
> Additionally, since the element count member must be set before accessing
> the annotated flexible array member, move its initialization earlier.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Fei Li <fei1.li@...el.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks
-- 
Gustavo

> ---
>   drivers/virt/acrn/acrn_drv.h | 2 +-
>   drivers/virt/acrn/mm.c       | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/virt/acrn/acrn_drv.h b/drivers/virt/acrn/acrn_drv.h
> index 5663c17ad37c..fb8438094f6f 100644
> --- a/drivers/virt/acrn/acrn_drv.h
> +++ b/drivers/virt/acrn/acrn_drv.h
> @@ -60,7 +60,7 @@ struct vm_memory_region_batch {
>   	u16			   reserved[3];
>   	u32			   regions_num;
>   	u64			   regions_gpa;
> -	struct vm_memory_region_op regions_op[];
> +	struct vm_memory_region_op regions_op[] __counted_by(regions_num);
>   };
>   
>   /**
> diff --git a/drivers/virt/acrn/mm.c b/drivers/virt/acrn/mm.c
> index b4ad8d452e9a..fa5d9ca6be57 100644
> --- a/drivers/virt/acrn/mm.c
> +++ b/drivers/virt/acrn/mm.c
> @@ -250,11 +250,11 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
>   		ret = -ENOMEM;
>   		goto unmap_kernel_map;
>   	}
> +	regions_info->regions_num = nr_regions;
>   
>   	/* Fill each vm_memory_region_op */
>   	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);
>   	user_vm_pa = memmap->user_vm_pa;
>   	i = 0;