linux-kernel - Re: [PATCH 1/3] x86: Honour passed pgprot in track_pfn_insert() and track_pfn

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Date:	Tue, 9 Feb 2016 15:24:44 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Matthew Wilcox <willy@...ux.intel.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 1/3] x86: Honour passed pgprot in track_pfn_insert() and
 track_pfn_remap()


* Matthew Wilcox <willy@...ux.intel.com> wrote:

> > I sure hope not.  If vm_page_prot was writable, something was already broken, 
> > because this is the vvar mapping, and the vvar mapping is VM_READ (and not 
> > even VM_MAYREAD).
> 
> I do beg yor pardon.  I thought you were inserting a readonly page into the 
> middle of a writable mapping.  Instead you're inserting a non-executable page 
> into the middle of a VM_READ | VM_EXEC mapping. Sorry for the confusion.  I 
> should have written:
> 
> "like your patch ends up mapping the HPET into userspace executable"
> 
> which is far less exciting.

Btw., a side note, an executable HPET page has its own dangers as well, for 
example because it always changes in value, it can probabilistically represent 
'sensible' (and dangerous) executable x86 instructions that exploits can return 
to.

So only mapping it readable (which Andy's patch attempts I think) is worthwile.

Thanks,

	Ingo