linux-kernel - Re: [PATCH v5 03/10] swiotlb: Map the buffer if it was unmapped by XPFO

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Date:   Wed, 20 Sep 2017 16:25:48 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tycho Andersen <tycho@...ker.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-hardening@...ts.openwall.com,
        Marco Benatto <marco.antonio.780@...il.com>,
        Juerg Haefliger <juerg.haefliger@...onical.com>,
        Juerg Haefliger <juerg.haefliger@....com>
Subject: Re: [PATCH v5 03/10] swiotlb: Map the buffer if it was unmapped by
 XPFO

On 09/20/2017 03:47 PM, Tycho Andersen wrote:
> 
>>> static inline void *skcipher_map(struct scatter_walk *walk)
>>> {
>>>         struct page *page = scatterwalk_page(walk);
>>>
>>>         return (PageHighMem(page) ? kmap_atomic(page) : page_address(page)) +
>>>                offset_in_page(walk->offset);
>>> }
>> Is there any better way to catch these?  Like, can we add some debugging
>> to check for XPFO pages in __va()?
> Yes, and perhaps also a debugging check in PageHighMem?

I'm not sure what PageHighMem() would check.  It's OK to use as long as
you don't depend on the contents of the page.
		
> Would __va have caught either of the two cases you've pointed out?
Yes.  __va() is what is eventually called by lowmem_page_address(),
which is only OK to call on things that are actually mapped into the kernel.