linux-kernel - RE: [PATCH v4 2/5] swiotlb: Enforce page alignment in swiotlb

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Date: Wed, 21 Feb 2024 23:36:04 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Will Deacon <will@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "kernel-team@...roid.com" <kernel-team@...roid.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, Christoph Hellwig
	<hch@....de>, Marek Szyprowski <m.szyprowski@...sung.com>, Robin Murphy
	<robin.murphy@....com>, Petr Tesarik <petr.tesarik1@...wei-partners.com>,
	Dexuan Cui <decui@...rosoft.com>, Nicolin Chen <nicolinc@...dia.com>
Subject: RE: [PATCH v4 2/5] swiotlb: Enforce page alignment in swiotlb_alloc()

From: Will Deacon <will@...nel.org> Sent: Wednesday, February 21, 2024 3:35 AM
> 
> When allocating pages from a restricted DMA pool in swiotlb_alloc(),
> the buffer address is blindly converted to a 'struct page *' that is
> returned to the caller. In the unlikely event of an allocation bug,
> page-unaligned addresses are not detected and slots can silently be
> double-allocated.
> 
> Add a simple check of the buffer alignment in swiotlb_alloc() to make
> debugging a little easier if something has gone wonky.
> 
> Cc: Christoph Hellwig <hch@....de>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Dexuan Cui <decui@...rosoft.com>
> Reviewed-by: Petr Tesarik <petr.tesarik1@...wei-partners.com>
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  kernel/dma/swiotlb.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 2ec2cc81f1a2..ab7fbb40bc55 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -1643,6 +1643,12 @@ struct page *swiotlb_alloc(struct device *dev,
> size_t size)
>  		return NULL;
> 
>  	tlb_addr = slot_addr(pool->start, index);
> +	if (unlikely(!PAGE_ALIGNED(tlb_addr))) {
> +		dev_WARN_ONCE(dev, 1, "Cannot allocate pages from non page-aligned swiotlb addr 0x%pa.\n",
> +			      &tlb_addr);
> +		swiotlb_release_slots(dev, tlb_addr);
> +		return NULL;
> +	}
> 
>  	return pfn_to_page(PFN_DOWN(tlb_addr));
>  }
> --
> 2.44.0.rc0.258.g7320e95886-goog

Reviewed-by: Michael Kelley <mhklinux@...look.com>