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[217.226.145.200]) by smtp.gmail.com with ESMTPSA id n10sm15999018edo.43.2020.08.18.10.27.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2020 10:27:20 -0700 (PDT) Received: from localhost.daheim ([127.0.0.1]) by debian64.daheim with esmtp (Exim 4.94) (envelope-from ) id 1k85OD-000B8U-AO; Tue, 18 Aug 2020 19:27:13 +0200 Subject: Re: [PATCH] p54: avoid accessing the data mapped to streaming DMA To: Jia-Ju Bai , kvalo@codeaurora.org, kuba@kernel.org Cc: linux-wireless@vger.kernel.org References: <20200802132949.26788-1-baijiaju@tsinghua.edu.cn> From: Christian Lamparter Message-ID: <0b432282-8d52-3004-6648-d97c03cdae28@gmail.com> Date: Tue, 18 Aug 2020 19:27:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200802132949.26788-1-baijiaju@tsinghua.edu.cn> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org Hello, sorry. Your mail got flagged by google mail as spam. :( On 2020-08-02 15:29, Jia-Ju Bai wrote: > 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. Interesting. Please bear with me here. From my understanding, the streaming direction is set to PCI_DMA_TODEVICE. So is it really possible for the hardware to interfere with the data without the IOMMU catching this? (That said, patch looks be fine. I'll need to dust off a old PCI PC to check this with real hardware, if requested.) Cheers, Christian > > Signed-off-by: Jia-Ju Bai > --- > 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; > >