This is a note to let you know that I've just added the patch titled wcn36xx: add proper DMA memory barriers in rx path to the 5.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: wcn36xx-add-proper-dma-memory-barriers-in-rx-path.patch and it can be found in the queue-5.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 516aae568e42eea7a56643c5dc73c49b75b4eb5f Author: Benjamin Li <benl@xxxxxxxxxxxx> Date: Fri Oct 22 17:15:28 2021 -0700 wcn36xx: add proper DMA memory barriers in rx path [ 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@xxxxxxxxxxxx> Signed-off-by: Kalle Valo <kvalo@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20211023001528.3077822-1-benl@xxxxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/net/wireless/ath/wcn36xx/dxe.c b/drivers/net/wireless/ath/wcn36xx/dxe.c index 0e0bbcd11300b..aff04ef662663 100644 --- a/drivers/net/wireless/ath/wcn36xx/dxe.c +++ b/drivers/net/wireless/ath/wcn36xx/dxe.c @@ -606,6 +606,10 @@ 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); @@ -616,9 +620,15 @@ 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; }