linux-hardening - Re: [PATCH][next] iommu/virtio: Add __counted_by for struct viommu_request and use struct

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Date: Tue, 10 Oct 2023 14:36:49 +0100
From: Jean-Philippe Brucker <jean-philippe@...aro.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	virtualization@...ts.linux-foundation.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] iommu/virtio: Add __counted_by for struct
 viommu_request and use struct_size()

On Mon, Oct 09, 2023 at 12:24:27PM -0600, Gustavo A. R. Silva 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 via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
> 
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Reviewed-by: Jean-Philippe Brucker <jean-philippe@...aro.org>

> ---
>  drivers/iommu/virtio-iommu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> index 17dcd826f5c2..379ebe03efb6 100644
> --- a/drivers/iommu/virtio-iommu.c
> +++ b/drivers/iommu/virtio-iommu.c
> @@ -85,7 +85,7 @@ struct viommu_request {
>  	void				*writeback;
>  	unsigned int			write_offset;
>  	unsigned int			len;
> -	char				buf[];
> +	char				buf[] __counted_by(len);
>  };
>  
>  #define VIOMMU_FAULT_RESV_MASK		0xffffff00
> @@ -230,7 +230,7 @@ static int __viommu_add_req(struct viommu_dev *viommu, void *buf, size_t len,
>  	if (write_offset <= 0)
>  		return -EINVAL;
>  
> -	req = kzalloc(sizeof(*req) + len, GFP_ATOMIC);
> +	req = kzalloc(struct_size(req, buf, len), GFP_ATOMIC);
>  	if (!req)
>  		return -ENOMEM;
>  
> -- 
> 2.34.1
>