linux-kernel - [PATCH v3] dma-mapping: set default segment_boundary_mask to ULONG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 14 Aug 2020 23:47:26 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     hch@....de, m.szyprowski@...sung.com, robin.murphy@....com
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] dma-mapping: set default segment_boundary_mask to ULONG_MAX

The default segment_boundary_mask was set to DMA_BIT_MAKS(32)
a decade ago by referencing SCSI/block subsystem, as a 32-bit
mask was good enough for most of the devices.

Now more and more drivers set dma_masks above DMA_BIT_MAKS(32)
while only a handful of them call dma_set_seg_boundary(). This
means that most drivers have a 4GB segmention boundary because
DMA API returns a 32-bit default value, though they might not
really have such a limit.

The default segment_boundary_mask should mean "no limit" since
the device doesn't explicitly set the mask. But a 32-bit mask
certainly limits those devices capable of 32+ bits addressing.

So this patch sets default segment_boundary_mask to ULONG_MAX.

Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
---

Changelog:
v2->v3
 * Resent -- no change
   v2 was sent 4 months ago https://lkml.org/lkml/2020/4/6/881
   but it has not got replied yet
v1->v2
 * Followed Robin's comments to revise the commit message by
   dropping one paragraph of not-entirely-true justification
   (no git-diff level change, so please ack if you tested v1)

 include/linux/dma-mapping.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 016b96b384bd..27df499aa041 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -628,7 +628,7 @@ static inline unsigned long dma_get_seg_boundary(struct device *dev)
 {
 	if (dev->dma_parms && dev->dma_parms->segment_boundary_mask)
 		return dev->dma_parms->segment_boundary_mask;
-	return DMA_BIT_MASK(32);
+	return ULONG_MAX;
 }

 static inline int dma_set_seg_boundary(struct device *dev, unsigned long mask)
-- 
2.17.1