linux-kernel - Re: [PATCH] mm/x86: AMD Bulldozer ASLR fix

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Date:	Tue, 31 Mar 2015 09:59:50 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Hector Marco-Gisbert <hecmargi@....es>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jan-Simon <dl9pf@....de>, linux-fsdevel@...r.kernel.org,
	kees Cook <keescook@...omium.org>,
	Ismael Ripoll <iripoll@...ca.upv.es>
Subject: Re: [PATCH] mm/x86: AMD Bulldozer ASLR fix


* Borislav Petkov <bp@...en8.de> wrote:

> On Sun, Mar 29, 2015 at 10:51:22AM +0200, Ingo Molnar wrote:
> > s/reduces the mmapped file's entropy by 3 bits
> > 
> > Which does:
> > 
> >  - a grammar fix
> > 
> >  - measure it in bits, as later on we are talking about randomness in 
> >    bits as well.
> 
> Fixed.
> 
> > Btw., does this limitation affect both executable and non-executable
> > mmap()s?
> 
> Only executable mappings.
> 
> > Because data mmap()s don't need this I$ related workaround, right? So
> > we could relax it for data-mmap()s?
> 
> Well, AFAIR, we wanted to keep this as less intrusive as possble. If
> we're going to relax this, one way to solve it would be to pass down
> @prot from do_mmap_pgoff() and friends to get_unmapped_area() which
> would need to touch other arches.
> 
> I'm not sure it is worth it...

Well, we could define arch_get_unmapped_area_exec(), and if an arch 
defines it, the mm code would call into it.

But yeah, it would add a function pointer to mm_struct, which I'm not 
sure is worth it.

Thanks,

	Ingo
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