[PATCH] atm: idt77252: avoid accessing the data mapped to streaming DMA

In queue_skb(), skb->data is mapped to streaming DMA on line 850:
  dma_map_single(..., skb->data, ...);

Then skb->data is accessed on lines 862 and 863:
  tbd->word_4 = (skb->data[0] << 24) | (skb->data[1] << 16) |
           (skb->data[2] <<  8) | (skb->data[3] <<  0);
and on lines 893 and 894:
  tbd->word_4 = (skb->data[0] << 24) | (skb->data[1] << 16) |
           (skb->data[2] <<  8) | (skb->data[3] <<  0);

These accesses may cause data inconsistency between CPU cache and
hardware.

To fix this problem, the calculation result of skb->data 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 <redacted>
---
 drivers/atm/idt77252.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/atm/idt77252.c b/drivers/atm/idt77252.c
index df51680e8931..65a3886f68c9 100644
--- a/drivers/atm/idt77252.c
+++ b/drivers/atm/idt77252.c

@@ -835,6 +835,7 @@ queue_skb(struct idt77252_dev *card, struct vc_map *vc,
 	unsigned long flags;
 	int error;
 	int aal;
+	u32 word4;
 
 	if (skb->len == 0) {
 		printk("%s: invalid skb->len (%d)\n", card->name, skb->len);

@@ -846,6 +847,8 @@ queue_skb(struct idt77252_dev *card, struct vc_map *vc,
 
 	tbd = &IDT77252_PRV_TBD(skb);
 	vcc = ATM_SKB(skb)->vcc;
+	word4 = (skb->data[0] << 24) | (skb->data[1] << 16) |
+			(skb->data[2] <<  8) | (skb->data[3] <<  0);
 
 	IDT77252_PRV_PADDR(skb) = dma_map_single(&card->pcidev->dev, skb->data,
 						 skb->len, DMA_TO_DEVICE);

@@ -859,8 +862,7 @@ queue_skb(struct idt77252_dev *card, struct vc_map *vc,
 		tbd->word_1 = SAR_TBD_OAM | ATM_CELL_PAYLOAD | SAR_TBD_EPDU;
 		tbd->word_2 = IDT77252_PRV_PADDR(skb) + 4;
 		tbd->word_3 = 0x00000000;
-		tbd->word_4 = (skb->data[0] << 24) | (skb->data[1] << 16) |
-			      (skb->data[2] <<  8) | (skb->data[3] <<  0);
+		tbd->word_4 = word4;
 
 		if (test_bit(VCF_RSV, &vc->flags))
 			vc = card->vcs[0];

@@ -890,8 +892,7 @@ queue_skb(struct idt77252_dev *card, struct vc_map *vc,
 
 		tbd->word_2 = IDT77252_PRV_PADDR(skb) + 4;
 		tbd->word_3 = 0x00000000;
-		tbd->word_4 = (skb->data[0] << 24) | (skb->data[1] << 16) |
-			      (skb->data[2] <<  8) | (skb->data[3] <<  0);
+		tbd->word_4 = word4;
 		break;
 
 	case ATM_AAL5:

-- 
2.17.1

From: Jia-Ju Bai <redacted>
Date: Sun,  2 Aug 2020 17:33:40 +0800

In queue_skb(), skb->data is mapped to streaming DMA on line 850:
  dma_map_single(..., skb->data, ...);

Then skb->data is accessed on lines 862 and 863:
  tbd->word_4 = (skb->data[0] << 24) | (skb->data[1] << 16) |
           (skb->data[2] <<  8) | (skb->data[3] <<  0);
and on lines 893 and 894:
  tbd->word_4 = (skb->data[0] << 24) | (skb->data[1] << 16) |
           (skb->data[2] <<  8) | (skb->data[3] <<  0);

These accesses may cause data inconsistency between CPU cache and
hardware.

To fix this problem, the calculation result of skb->data 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 <redacted>

Applied.