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Date: Wed, 20 Sep 2017 16:47:39 -0600
From: Tycho Andersen <tycho@...ker.com>
To: Dave Hansen <dave.hansen@...el.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 Wed, Sep 20, 2017 at 09:19:56AM -0700, Dave Hansen wrote:
> On 08/09/2017 01:07 PM, Tycho Andersen wrote:
> > --- a/lib/swiotlb.c
> > +++ b/lib/swiotlb.c
> > @@ -420,8 +420,9 @@ static void swiotlb_bounce(phys_addr_t orig_addr, phys_addr_t tlb_addr,
> >  {
> >  	unsigned long pfn = PFN_DOWN(orig_addr);
> >  	unsigned char *vaddr = phys_to_virt(tlb_addr);
> > +	struct page *page = pfn_to_page(pfn);
> >  
> > -	if (PageHighMem(pfn_to_page(pfn))) {
> > +	if (PageHighMem(page) || xpfo_page_is_unmapped(page)) {
> >  		/* The buffer does not have a mapping.  Map it in and copy */
> >  		unsigned int offset = orig_addr & ~PAGE_MASK;
> >  		char *buffer;
> 
> This is a little scary.  I wonder how many more of these are in the
> kernel, like:

I don't know, but I assume several :)

> > 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? Would __va
have caught either of the two cases you've pointed out?

Tycho

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