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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Liu Shixin <liushixin2@huawei.com>
Subject: [PATCH 4.19 49/49] swiotlb: skip swiotlb_bounce when orig_addr is zero
Date:   Thu, 30 Jun 2022 15:47:02 +0200
Message-Id: <20220630133235.317860776@linuxfoundation.org>
In-Reply-To: <20220630133233.910803744@linuxfoundation.org>
References: <20220630133233.910803744@linuxfoundation.org>
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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>
---
 kernel/dma/swiotlb.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -594,7 +594,8 @@ 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;
 }