[PATCH 4.14 35/35] swiotlb: skip swiotlb_bounce when orig_addr is zero

Greg Kroah-Hartman
2022-06-30T13:57:03Z

From: Liu Shixin <liushixin2@huawei.com>

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@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
lib/swiotlb.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -607,7 +607,8 @@ found:
* 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);