linux-kernel - [PATCH stable 4.9,4.14] swiotlb: skip swiotlb_bounce when orig

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Date:   Thu, 30 Jun 2022 19:32:25 +0800
From:   Liu Shixin <liushixin2@...wei.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Christoph Hellwig <hch@....de>,
        Ovidiu Panait <ovidiu.panait@...driver.com>,
        Ben Hutchings <ben@...adent.org.uk>
CC:     <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        Liu Shixin <liushixin2@...wei.com>
Subject: [PATCH stable 4.9,4.14] swiotlb: skip swiotlb_bounce when orig_addr is zero

After patch ddbd89deb7d3 ("swiotlb: fix info leak with DMA_FROM_DEVICE"),
swiotlb_bounce will be called in swiotlb_tbl_map_single unconditionally.
This requires that the physical address must be valid, which is not always
true on stable-4.19 or earlier version.
On stable-4.19, swiotlb_alloc_buffer will call swiotlb_tbl_map_single with
orig_addr equal to zero, which cause such a panic:

Unable to handle kernel paging request at virtual address ffffb77a40000000
...
pc : __memcpy+0x100/0x180
lr : swiotlb_bounce+0x74/0x88
...
Call trace:
 __memcpy+0x100/0x180
 swiotlb_tbl_map_single+0x2c8/0x338
 swiotlb_alloc+0xb4/0x198
 __dma_alloc+0x84/0x1d8
 ...

On stable-4.9 and stable-4.14, swiotlb_alloc_coherent wille call map_single
with orig_addr equal to zero, which can cause same panic.

Fix this by skipping swiotlb_bounce when orig_addr is zero.

Fixes: ddbd89deb7d3 ("swiotlb: fix info leak with DMA_FROM_DEVICE")
Signed-off-by: Liu Shixin <liushixin2@...wei.com>
---
 lib/swiotlb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index bdc2b89870e3..e162cb464ee4 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -607,7 +607,8 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 	 * unconditional bounce may prevent leaking swiotlb content (i.e.
 	 * kernel memory) to user-space.
 	 */
-	swiotlb_bounce(orig_addr, tlb_addr, size, DMA_TO_DEVICE);
+	if (orig_addr)
+		swiotlb_bounce(orig_addr, tlb_addr, size, DMA_TO_DEVICE);
 	return tlb_addr;
 }
 EXPORT_SYMBOL_GPL(swiotlb_tbl_map_single);
-- 
2.25.1