linux-kernel - Re: [PATCH 70/82] remoteproc: Refactor intentional wrap-around test

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Message-ID: <nfxldxqon7xfzqvxhhspzfoueebgczjbner67vtibeeukxd4oa@xgeaofdfgezz>
Date: Tue, 6 Feb 2024 10:55:21 -0800
From: Bjorn Andersson <andersson@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: linux-hardening@...r.kernel.org, 
	Mathieu Poirier <mathieu.poirier@...aro.org>, linux-remoteproc@...r.kernel.org, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 70/82] remoteproc: Refactor intentional wrap-around test

On Mon, Jan 22, 2024 at 04:27:45PM -0800, Kees Cook wrote:
> In an effort to separate intentional arithmetic wrap-around from
> unexpected wrap-around, we need to refactor places that depend on this
> kind of math. One of the most common code patterns of this is:
> 
> 	VAR + value < VAR
> 
> Notably, this is considered "undefined behavior" for signed and pointer
> types, which the kernel works around by using the -fno-strict-overflow
> option in the build[1] (which used to just be -fwrapv). Regardless, we
> want to get the kernel source to the position where we can meaningfully
> instrument arithmetic wrap-around conditions and catch them when they
> are unexpected, regardless of whether they are signed[2], unsigned[3],
> or pointer[4] types.
> 
> Refactor open-coded wrap-around addition test to use add_would_overflow().
> This paves the way to enabling the wrap-around sanitizers in the future.
> 
> Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
> Link: https://github.com/KSPP/linux/issues/26 [2]
> Link: https://github.com/KSPP/linux/issues/27 [3]
> Link: https://github.com/KSPP/linux/issues/344 [4]
> Cc: Bjorn Andersson <andersson@...nel.org>

Acked-by: Bjorn Andersson <andersson@...nel.org>

Regards,
Bjorn


> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: linux-remoteproc@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/remoteproc/pru_rproc.c             | 2 +-
>  drivers/remoteproc/remoteproc_elf_loader.c | 2 +-
>  drivers/remoteproc/remoteproc_virtio.c     | 4 ++--
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/remoteproc/pru_rproc.c b/drivers/remoteproc/pru_rproc.c
> index 327f0c7ee3d6..834249ee3dd3 100644
> --- a/drivers/remoteproc/pru_rproc.c
> +++ b/drivers/remoteproc/pru_rproc.c
> @@ -893,7 +893,7 @@ pru_rproc_find_interrupt_map(struct device *dev, const struct firmware *fw)
>  			continue;
>  
>  		/* make sure we have the entire irq map */
> -		if (offset + size > fw->size || offset + size < size) {
> +		if (offset + size > fw->size || add_would_overflow(size, offset)) {
>  			dev_err(dev, ".pru_irq_map section truncated\n");
>  			return ERR_PTR(-EINVAL);
>  		}
> diff --git a/drivers/remoteproc/remoteproc_elf_loader.c b/drivers/remoteproc/remoteproc_elf_loader.c
> index 94177e416047..b9231cf46d68 100644
> --- a/drivers/remoteproc/remoteproc_elf_loader.c
> +++ b/drivers/remoteproc/remoteproc_elf_loader.c
> @@ -278,7 +278,7 @@ find_table(struct device *dev, const struct firmware *fw)
>  		table = (struct resource_table *)(elf_data + offset);
>  
>  		/* make sure we have the entire table */
> -		if (offset + size > fw_size || offset + size < size) {
> +		if (offset + size > fw_size || add_would_overflow(size, offset)) {
>  			dev_err(dev, "resource table truncated\n");
>  			return NULL;
>  		}
> diff --git a/drivers/remoteproc/remoteproc_virtio.c b/drivers/remoteproc/remoteproc_virtio.c
> index 83d76915a6ad..58742c666e35 100644
> --- a/drivers/remoteproc/remoteproc_virtio.c
> +++ b/drivers/remoteproc/remoteproc_virtio.c
> @@ -298,7 +298,7 @@ static void rproc_virtio_get(struct virtio_device *vdev, unsigned int offset,
>  	rsc = (void *)rvdev->rproc->table_ptr + rvdev->rsc_offset;
>  	cfg = &rsc->vring[rsc->num_of_vrings];
>  
> -	if (offset + len > rsc->config_len || offset + len < len) {
> +	if (offset + len > rsc->config_len || add_would_overflow(len, offset)) {
>  		dev_err(&vdev->dev, "rproc_virtio_get: access out of bounds\n");
>  		return;
>  	}
> @@ -316,7 +316,7 @@ static void rproc_virtio_set(struct virtio_device *vdev, unsigned int offset,
>  	rsc = (void *)rvdev->rproc->table_ptr + rvdev->rsc_offset;
>  	cfg = &rsc->vring[rsc->num_of_vrings];
>  
> -	if (offset + len > rsc->config_len || offset + len < len) {
> +	if (offset + len > rsc->config_len || add_would_overflow(len, offset)) {
>  		dev_err(&vdev->dev, "rproc_virtio_set: access out of bounds\n");
>  		return;
>  	}
> -- 
> 2.34.1
>