netdev - [PATCH] p54: avoid accessing the data mapped to streaming DMA

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Message-Id: <20200802132949.26788-1-baijiaju@tsinghua.edu.cn>
Date:   Sun,  2 Aug 2020 21:29:49 +0800
From:   Jia-Ju Bai <baijiaju@...nghua.edu.cn>
To:     chunkeey@...glemail.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, Jia-Ju Bai <baijiaju@...nghua.edu.cn>
Subject: [PATCH] p54: avoid accessing the data mapped to streaming DMA

In p54p_tx(), skb->data is mapped to streaming DMA on line 337:
  mapping = pci_map_single(..., skb->data, ...);

Then skb->data is accessed on line 349:
  desc->device_addr = ((struct p54_hdr *)skb->data)->req_id;

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

To fix this problem, ((struct p54_hdr *)skb->data)->req_id is stored in
a local variable before DMA mapping, and then the driver accesses this
local variable instead of skb->data.

Signed-off-by: Jia-Ju Bai <baijiaju@...nghua.edu.cn>
---
 drivers/net/wireless/intersil/p54/p54pci.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intersil/p54/p54pci.c b/drivers/net/wireless/intersil/p54/p54pci.c
index 80ad0b7eaef4..f8c6027cab6b 100644
--- a/drivers/net/wireless/intersil/p54/p54pci.c
+++ b/drivers/net/wireless/intersil/p54/p54pci.c
@@ -329,10 +329,12 @@ static void p54p_tx(struct ieee80211_hw *dev, struct sk_buff *skb)
 	struct p54p_desc *desc;
 	dma_addr_t mapping;
 	u32 idx, i;
+	__le32 device_addr;
 
 	spin_lock_irqsave(&priv->lock, flags);
 	idx = le32_to_cpu(ring_control->host_idx[1]);
 	i = idx % ARRAY_SIZE(ring_control->tx_data);
+	device_addr = ((struct p54_hdr *)skb->data)->req_id;
 
 	mapping = pci_map_single(priv->pdev, skb->data, skb->len,
 				 PCI_DMA_TODEVICE);
@@ -346,7 +348,7 @@ static void p54p_tx(struct ieee80211_hw *dev, struct sk_buff *skb)
 
 	desc = &ring_control->tx_data[i];
 	desc->host_addr = cpu_to_le32(mapping);
-	desc->device_addr = ((struct p54_hdr *)skb->data)->req_id;
+	desc->device_addr = device_addr;
 	desc->len = cpu_to_le16(skb->len);
 	desc->flags = 0;
 
-- 
2.17.1