linux-kernel - Re: [PATCH v2 1/4] rtlwifi: rtl8188ee: avoid accessing the data mapped to streaming DMA

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Date:   Wed, 18 Nov 2020 11:20:24 -0600
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, pkshih@...ltek.com,
        kvalo@...eaurora.org, davem@...emloft.net, kuba@...nel.org
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] rtlwifi: rtl8188ee: avoid accessing the data
 mapped to streaming DMA

On 11/17/20 7:53 PM, Jia-Ju Bai wrote:
> In rtl88ee_tx_fill_cmddesc(), skb->data is mapped to streaming DMA on
> line 677:
>    dma_addr_t mapping = dma_map_single(..., skb->data, ...);
> 
> On line 680, skb->data is assigned to hdr after cast:
>    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)(skb->data);
> 
> Then hdr->frame_control is accessed on line 681:
>    __le16 fc = hdr->frame_control;
> 
> This DMA access may cause data inconsistency between CPU and hardwre.
> 
> To fix this bug, hdr->frame_control is accessed before the DMA mapping.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>   drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)

What changed between v1 and v2?

As outlined in Documentation/process/submitting-patches.rst, you should add a 
'---' marker and descrive what was changed. I usually summarize the changes, but 
it is also possible to provide a diffstat of the changes as the above file shows.

Larry

> 
> diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c b/drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c
> index b9775eec4c54..c948dafa0c80 100644
> --- a/drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c
> +++ b/drivers/net/wireless/realtek/rtlwifi/rtl8188ee/trx.c
> @@ -674,12 +674,12 @@ void rtl88ee_tx_fill_cmddesc(struct ieee80211_hw *hw,
>   	u8 fw_queue = QSLT_BEACON;
>   	__le32 *pdesc = (__le32 *)pdesc8;
>   
> -	dma_addr_t mapping = dma_map_single(&rtlpci->pdev->dev, skb->data,
> -					    skb->len, DMA_TO_DEVICE);
> -
>   	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)(skb->data);
>   	__le16 fc = hdr->frame_control;
>   
> +	dma_addr_t mapping = dma_map_single(&rtlpci->pdev->dev, skb->data,
> +					    skb->len, DMA_TO_DEVICE);
> +
>   	if (dma_mapping_error(&rtlpci->pdev->dev, mapping)) {
>   		rtl_dbg(rtlpriv, COMP_SEND, DBG_TRACE,
>   			"DMA mapping error\n");
>