[PATCH] mtk-sd: Prevent memory corruption from DMA map failure

[Masami Hiramatsu (Google)]

Ping?

I think there will be another bug which leaks the resources
to cause this failure case. But anyway, without this fix,
if DMA preparation fails but runs a DMA, it will overwrite
the previous read buffer memory.

Thank you,

On Thu, 12 Jun 2025 20:26:10 +0900
"Masami Hiramatsu (Google)" <mhiramat at kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat at kernel.org>
> 
> If msdc_prepare_data() fails to map the DMA region, the request is
> not prepared for data receiving, but msdc_start_data() proceeds
> the DMA with previous setting.
> Since this will lead a memory corruption, we have to stop the
> request operation soon after the msdc_prepare_data() fails to
> prepare it.
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat at kernel.org>
> ---
>  drivers/mmc/host/mtk-sd.c |   17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/mtk-sd.c b/drivers/mmc/host/mtk-sd.c
> index 3594010bc229..56b4999fe58f 100644
> --- a/drivers/mmc/host/mtk-sd.c
> +++ b/drivers/mmc/host/mtk-sd.c
> @@ -834,6 +834,11 @@ static void msdc_prepare_data(struct msdc_host *host, struct mmc_data *data)
>  	}
>  }
>  
> +static bool msdc_data_prepared(struct mmc_data *data)
> +{
> +	return data->host_cookie & MSDC_PREPARE_FLAG;
> +}
> +
>  static void msdc_unprepare_data(struct msdc_host *host, struct mmc_data *data)
>  {
>  	if (data->host_cookie & MSDC_ASYNC_FLAG)
> @@ -1466,8 +1471,18 @@ static void msdc_ops_request(struct mmc_host *mmc, struct mmc_request *mrq)
>  	WARN_ON(!host->hsq_en && host->mrq);
>  	host->mrq = mrq;
>  
> -	if (mrq->data)
> +	if (mrq->data) {
>  		msdc_prepare_data(host, mrq->data);
> +		if (!msdc_data_prepared(mrq->data)) {
> +			/*
> +			 * Failed to prepare DMA area, fail fast before
> +			 * starting any commands.
> +			 */
> +			mrq->cmd->error = -ENOSPC;
> +			mmc_request_done(mmc_from_priv(host), mrq);
> +			return;
> +		}
> +	}
>  
>  	/* if SBC is required, we have HW option and SW option.
>  	 * if HW option is enabled, and SBC does not have "special" flags,
> 


-- 
Masami Hiramatsu (Google) <mhiramat at kernel.org>