linux-kernel - Re: [syzbot] [iommu?] kernel BUG in dma_alloc

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Message-ID: <32ad3314-c2bc-4d3c-b4ae-28f96ac965af@linux.dev>
Date: Thu, 17 Oct 2024 10:48:00 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Christoph Hellwig <hch@....de>
Cc: syzbot <syzbot+b4bfacdec173efaa8567@...kaller.appspotmail.com>,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 m.szyprowski@...sung.com, robin.murphy@....com,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [iommu?] kernel BUG in dma_alloc_attrs

On 10/17/24 10:40, Christoph Hellwig wrote:
> On Thu, Oct 17, 2024 at 10:31:40AM -0400, Sean Anderson wrote:
>> On 10/16/24 04:02, Christoph Hellwig wrote:
>> > The problem is that the dma alloc/free tracing calls virt_to_phys
>> > on the allocated/free memory.  But that memory can be vmalloced as
>> > in this case.  I think we don't have weirdo allocators or pools any
>> > more that are neither in the direct kernel mapping or vmalloc, so
>> > we might be able to do an
>> > 
>> > 		if (is_vmalloc_addr())
>> > 			page_to_phys(vmalloc_to_page()))
>> 
>> Do we need offset_in_page?
> 
> The DMA allocator always returns page aligned memory.
> 
>> Since this function returns a virtual address, I think that would be
>> fine.
> 
> Ok, I'll look into that.  I'll need to check if %p gets obsfucated
> for traces like it does for normal dmesg first, though.
> 

I have a patch written up for this; will send it after testing.

--Sean