linux-kernel - Re: [PATCH] dma-remap: fix dma_common_find

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

Message-ID: <c71603c6-fa05-4cd6-836a-4bbf55ba5ca9@samsung.com>
Date: Mon, 15 Dec 2025 09:13:38 +0100
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Christoph Hellwig <hch@...radead.org>, Andrei-Edward Popa
	<andrei.popa105@...oo.com>
Cc: robin.murphy@....com, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-remap: fix dma_common_find_pages() page lookup for
 offsets

On 15.12.2025 06:57, Christoph Hellwig wrote:
> On Fri, Dec 12, 2025 at 10:09:14PM +0200, Andrei-Edward Popa wrote:
>> dma_common_find_pages() previously assumed that the CPU virtual address
>> always pointed to the start of a DMA-coherent allocation. This fails when
>> memory is allocated via dma_alloc_attrs() without DMA_ATTR_FORCE_CONTIGUOUS
>> and then subdivided into smaller blocks using a gen_pool, relevant only
>> when an IOMMU is enabled.
>>
>> In such cases, userspace may request a mapping via dma_mmap_attrs()
>> for a CPU address that is offset inside the original allocation. The
>> previous code could return the wrong struct page pointer.
> No, you can't mmap part of a dma coherent allocation.  What caller is
> trying to do this?  It needs to be fixed instead.

I wonder if this was ever explicitly stated.

dma_mmap_coherent() was initially added for mmapeing a 
dma_alloc_coherent()-allocated buffer for fbdev and alsa, and at least 
the first one allowed to mmap the buffer partially or starting at 
non-zero offset. I doubt that this feature was useful for anything, but 
I'm quite sure this was at least allowed and there were some comments in 
the code about that.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland