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

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Message-ID: <20241017144020.GA22666@lst.de>
Date: Thu, 17 Oct 2024 16:40:20 +0200
From: Christoph Hellwig <hch@....de>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: Christoph Hellwig <hch@....de>,
	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 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.