Re: [PATCH] rtl8180: avoid accessing the data mapped to streaming DMA

[Maciej S. Szmigiero]

On 19.10.2020 04:54, Jia-Ju Bai wrote:
> In rtl8180_tx(), skb->data is mapped to streaming DMA on line 476:
>   mapping = dma_map_single(..., skb->data, ...);
> 
> On line 459, skb->data is assigned to hdr after cast:
>   struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
> 
> Then hdr->seq_ctrl is accessed on lines 540 and 541:
>   hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
>   hdr->seq_ctrl |= cpu_to_le16(priv->seqno);
> 
> These DMA accesses may cause data inconsistency between CPU and hardwre.
> 
> To fix this problem, hdr->seq_ctrl is accessed before the DMA mapping.
> 

This looks like a bug fix to me, shouldn't this have a Fixes: tag and
be CC'ed to stable@?

Maciej

Re: [PATCH] rtl8180: avoid accessing the data mapped to streaming DMA

[Jakub Kicinski]

On Mon, 19 Oct 2020 10:54:20 +0800 Jia-Ju Bai wrote:
> + if (info->flags & IEEE80211_TX_CTL_ASSIGN_SEQ) {
> + if (info->flags & IEEE80211_TX_CTL_FIRST_FRAGMENT)
> + priv->seqno += 0x10;
> + hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
> + hdr->seq_ctrl |= cpu_to_le16(priv->seqno);
> + }
> +
>   mapping = dma_map_single(>pdev->dev, skb->data, skb->len,
>DMA_TO_DEVICE);
>  
> @@ -534,13 +541,6 @@ static void rtl8180_tx(struct ieee80211_hw *dev,
>  
>   spin_lock_irqsave(>lock, flags);
>  
> - if (info->flags & IEEE80211_TX_CTL_ASSIGN_SEQ) {
> - if (info->flags & IEEE80211_TX_CTL_FIRST_FRAGMENT)
> - priv->seqno += 0x10;

You're taking the priv->seqno access and modification from under
priv->lock. Is that okay?

[PATCH] rtl8180: avoid accessing the data mapped to streaming DMA

[Jia-Ju Bai]

In rtl8180_tx(), skb->data is mapped to streaming DMA on line 476:
  mapping = dma_map_single(..., skb->data, ...);

On line 459, skb->data is assigned to hdr after cast:
  struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;

Then hdr->seq_ctrl is accessed on lines 540 and 541:
  hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
  hdr->seq_ctrl |= cpu_to_le16(priv->seqno);

These DMA accesses may cause data inconsistency between CPU and hardwre.

To fix this problem, hdr->seq_ctrl is accessed before the DMA mapping.

Signed-off-by: Jia-Ju Bai 
---
 drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c | 14 +++---
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c 
b/drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c
index 2477e18c7cae..cc73014aa5f3 100644
--- a/drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c
+++ b/drivers/net/wireless/realtek/rtl818x/rtl8180/dev.c
@@ -473,6 +473,13 @@ static void rtl8180_tx(struct ieee80211_hw *dev,
prio = skb_get_queue_mapping(skb);
ring = >tx_ring[prio];
 
+   if (info->flags & IEEE80211_TX_CTL_ASSIGN_SEQ) {
+   if (info->flags & IEEE80211_TX_CTL_FIRST_FRAGMENT)
+   priv->seqno += 0x10;
+   hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
+   hdr->seq_ctrl |= cpu_to_le16(priv->seqno);
+   }
+
mapping = dma_map_single(>pdev->dev, skb->data, skb->len,
 DMA_TO_DEVICE);
 
@@ -534,13 +541,6 @@ static void rtl8180_tx(struct ieee80211_hw *dev,
 
spin_lock_irqsave(>lock, flags);
 
-   if (info->flags & IEEE80211_TX_CTL_ASSIGN_SEQ) {
-   if (info->flags & IEEE80211_TX_CTL_FIRST_FRAGMENT)
-   priv->seqno += 0x10;
-   hdr->seq_ctrl &= cpu_to_le16(IEEE80211_SCTL_FRAG);
-   hdr->seq_ctrl |= cpu_to_le16(priv->seqno);
-   }
-
idx = (ring->idx + skb_queue_len(>queue)) % ring->entries;
entry = >desc[idx];
 
-- 
2.17.1