linux-kernel - Re: [PATCH 02/21] arm64/iommu: improve mmap bounds checking

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Date:   Tue, 9 Apr 2019 16:12:51 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     Joerg Roedel <joro@...tes.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/21] arm64/iommu: improve mmap bounds checking

On 07/04/2019 07:59, Christoph Hellwig wrote:
> On Fri, Apr 05, 2019 at 06:30:52PM +0100, Robin Murphy wrote:
>> On 27/03/2019 08:04, Christoph Hellwig wrote:
>>> The nr_pages checks should be done for all mmap requests, not just those
>>> using remap_pfn_range.
>>
>> Hmm, the logic in iommu_dma_mmap() inherently returns an error for the "off
>>> = nr_pages" case already. It's also supposed to be robust against the
>> "vma_pages(vma) > nr_pages - off" condition, although by making the partial
>> mapping and treating it as a success, rather than doing nothing and
>> returning an error. What's the exact motivation here?
> 
> Have one error check at the front of the function that is identical
> to the mmap checks in the other dma_map_ops instances so that:
> 
>   a) we get the same error behavior for partial requests everywhere
>   b) we can lift these checks into common code in the next round.
> 

Fair enough, but in that case why isn't the dma_mmap_from_coherent() 
path also covered?

Robin.