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From:   Jia-Ju Bai <baijiaju@tsinghua.edu.cn>
To:     3chas3@gmail.com
Cc:     linux-atm-general@lists.sourceforge.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jia-Ju Bai <baijiaju@tsinghua.edu.cn>
Subject: [PATCH] atm: eni: avoid accessing the data mapped to streaming DMA
Date:   Sun,  2 Aug 2020 17:16:11 +0800
Message-Id: <20200802091611.24331-1-baijiaju@tsinghua.edu.cn>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

In do_tx(), skb->data is mapped to streaming DMA on line 1111:
  paddr = dma_map_single(...,skb->data,DMA_TO_DEVICE);

Then skb->data is accessed on line 1153:
  (skb->data[3] & 0xf)

This access may cause data inconsistency between CPU cache and hardware.

To fix this problem, skb->data[3] is assigned to a local variable before
DMA mapping, and then the driver accesses this local variable instead of
skb->data[3].

Signed-off-by: Jia-Ju Bai <baijiaju@tsinghua.edu.cn>
---
 drivers/atm/eni.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/atm/eni.c b/drivers/atm/eni.c
index 17d47ad03ab7..09f4e2f41363 100644
--- a/drivers/atm/eni.c
+++ b/drivers/atm/eni.c
@@ -1034,6 +1034,7 @@ static enum enq_res do_tx(struct sk_buff *skb)
 	u32 dma_rd,dma_wr;
 	u32 size; /* in words */
 	int aal5,dma_size,i,j;
+	unsigned char skb_data3;
 
 	DPRINTK(">do_tx\n");
 	NULLCHECK(skb);
@@ -1108,6 +1109,7 @@ DPRINTK("iovcnt = %d\n",skb_shinfo(skb)->nr_frags);
 		    vcc->dev->number);
 		return enq_jam;
 	}
+	skb_data3 = skb->data[3];
 	paddr = dma_map_single(&eni_dev->pci_dev->dev,skb->data,skb->len,
 			       DMA_TO_DEVICE);
 	ENI_PRV_PADDR(skb) = paddr;
@@ -1150,7 +1152,7 @@ DPRINTK("doing direct send\n"); /* @@@ well, this doesn't work anyway */
 	    (size/(ATM_CELL_PAYLOAD/4)),tx->send+tx->tx_pos*4);
 /*printk("dsc = 0x%08lx\n",(unsigned long) readl(tx->send+tx->tx_pos*4));*/
 	writel((vcc->vci << MID_SEG_VCI_SHIFT) |
-            (aal5 ? 0 : (skb->data[3] & 0xf)) |
+            (aal5 ? 0 : (skb_data3 & 0xf)) |
 	    (ATM_SKB(skb)->atm_options & ATM_ATMOPT_CLP ? MID_SEG_CLP : 0),
 	    tx->send+((tx->tx_pos+1) & (tx->words-1))*4);
 	DPRINTK("size: %d, len:%d\n",size,skb->len);
-- 
2.17.1