linux-kernel - Re: [PATCH] media: mtk-vpu: avoid unaligned access to DTCM buffer.

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Date:   Fri, 14 Feb 2020 11:52:45 +0100
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Hsin-Yi Wang <hsinyi@...omium.org>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Minghsiu Tsai <minghsiu.tsai@...iatek.com>,
        Houlong Wei <houlong.wei@...iatek.com>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-media@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: mtk-vpu: avoid unaligned access to DTCM buffer.

Hi Hsin-Yi Wang,

On 2/10/20 4:53 AM, Hsin-Yi Wang wrote:
> struct vpu_run *run in vpu_init_ipi_handler() is an ioremapped DTCM (Data
> Tightly Coupled Memory) buffer shared with AP.  It's not able to do
> unaligned access. Otherwise kernel would crash due to unable to handle
> kernel paging request.
> 
> struct vpu_run {
> 	u32 signaled;
> 	char fw_ver[VPU_FW_VER_LEN];
> 	unsigned int	dec_capability;
> 	unsigned int	enc_capability;
> 	wait_queue_head_t wq;
> };
> 
> fw_ver starts at 4 byte boundary. If system enables
> CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, strscpy() will do
> read_word_at_a_time(), which tries to read 8-byte: *(unsigned long *)addr
> 
> Copy the string by memcpy_fromio() for this buffer to avoid unaligned
> access.
> 
> Fixes: 85709cbf1524 ("media: replace strncpy() by strscpy()")
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>

This patch results in the following sparse warnings:

sparse: WARNINGS
SPARSE:mtk-vpu/mtk_vpu.c mtk-vpu/mtk_vpu.c:834:52:  warning: incorrect type in argument 3 (incompatible argument 1 (different address spaces))
SPARSE:mtk-vpu/mtk_vpu.c mtk-vpu/mtk_vpu.c:609:29:  warning: dereference of noderef expression
SPARSE:mtk-vpu/mtk_vpu.c mtk-vpu/mtk_vpu.c:613:35:  warning: dereference of noderef expression
SPARSE:mtk-vpu/mtk_vpu.c mtk-vpu/mtk_vpu.c:614:35:  warning: dereference of noderef expression

Can you take a look?

Regards,

	Hans

> ---
>  drivers/media/platform/mtk-vpu/mtk_vpu.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/platform/mtk-vpu/mtk_vpu.c b/drivers/media/platform/mtk-vpu/mtk_vpu.c
> index a768707abb94..e705e85d6f5a 100644
> --- a/drivers/media/platform/mtk-vpu/mtk_vpu.c
> +++ b/drivers/media/platform/mtk-vpu/mtk_vpu.c
> @@ -600,13 +600,16 @@ int vpu_load_firmware(struct platform_device *pdev)
>  }
>  EXPORT_SYMBOL_GPL(vpu_load_firmware);
>  
> -static void vpu_init_ipi_handler(void *data, unsigned int len, void *priv)
> +static void vpu_init_ipi_handler(void __iomem *data, unsigned int len,
> +				 void *priv)
>  {
>  	struct mtk_vpu *vpu = (struct mtk_vpu *)priv;
> -	struct vpu_run *run = (struct vpu_run *)data;
> +	struct vpu_run __iomem *run = data;
>  
>  	vpu->run.signaled = run->signaled;
> -	strscpy(vpu->run.fw_ver, run->fw_ver, sizeof(vpu->run.fw_ver));
> +	memcpy_fromio(vpu->run.fw_ver, run->fw_ver, sizeof(vpu->run.fw_ver));
> +	/* Make sure the string is NUL-terminated */
> +	vpu->run.fw_ver[sizeof(vpu->run.fw_ver) - 1] = '\0';
>  	vpu->run.dec_capability = run->dec_capability;
>  	vpu->run.enc_capability = run->enc_capability;
>  	wake_up_interruptible(&vpu->run.wq);
>