From: Benjamin Li benl@squareup.com
[ Upstream commit 9bfe38e064af5decba2ffce66a2958ab8b10eaa4 ]
This is essentially exactly following the dma_wmb()/dma_rmb() usage instructions in Documentation/memory-barriers.txt.
The theoretical races here are:
1. DXE (the DMA Transfer Engine in the Wi-Fi subsystem) seeing the dxe->ctrl & WCN36xx_DXE_CTRL_VLD write before the dxe->dst_addr_l write, thus performing DMA into the wrong address.
2. CPU reading dxe->dst_addr_l before DXE unsets dxe->ctrl & WCN36xx_DXE_CTRL_VLD. This should generally be harmless since DXE doesn't write dxe->dst_addr_l (no risk of freeing the wrong skb).
Fixes: 8e84c2582169 ("wcn36xx: mac80211 driver for Qualcomm WCN3660/WCN3680 hardware") Signed-off-by: Benjamin Li benl@squareup.com Signed-off-by: Kalle Valo kvalo@codeaurora.org Link: https://lore.kernel.org/r/20211023001528.3077822-1-benl@squareup.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/wireless/ath/wcn36xx/dxe.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/net/wireless/ath/wcn36xx/dxe.c b/drivers/net/wireless/ath/wcn36xx/dxe.c index bab30f7a443ce..4da25e84793b7 100644 --- a/drivers/net/wireless/ath/wcn36xx/dxe.c +++ b/drivers/net/wireless/ath/wcn36xx/dxe.c @@ -563,6 +563,10 @@ static int wcn36xx_rx_handle_packets(struct wcn36xx *wcn, dxe = ctl->desc;
while (!(READ_ONCE(dxe->ctrl) & WCN36xx_DXE_CTRL_VLD)) { + /* do not read until we own DMA descriptor */ + dma_rmb(); + + /* read/modify DMA descriptor */ skb = ctl->skb; dma_addr = dxe->dst_addr_l; ret = wcn36xx_dxe_fill_skb(wcn->dev, ctl, GFP_ATOMIC); @@ -573,9 +577,15 @@ static int wcn36xx_rx_handle_packets(struct wcn36xx *wcn, dma_unmap_single(wcn->dev, dma_addr, WCN36XX_PKT_SIZE, DMA_FROM_DEVICE); wcn36xx_rx_skb(wcn, skb); - } /* else keep old skb not submitted and use it for rx DMA */ + } + /* else keep old skb not submitted and reuse it for rx DMA + * (dropping the packet that it contained) + */
+ /* flush descriptor changes before re-marking as valid */ + dma_wmb(); dxe->ctrl = ctrl; + ctl = ctl->next; dxe = ctl->desc; }