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

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Message-ID: <20150329085122.GA25177@gmail.com>
Date:	Sun, 29 Mar 2015 10:51:22 +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:

> From: Hector Marco-Gisbert <hecmargi@....es>
> Date: Fri, 27 Mar 2015 12:38:21 +0100
> Subject: [PATCH] x86/mm: Improve AMD Bulldozer ASLR fix
> 
> The ASLR implementation needs to special-case AMD F15h processors by
> clearing out bits [14:12] of the virtual address in order to avoid I$
> cross invalidations and thus performance penalty for certain workloads.
> For details, see:
> 
>   dfb09f9b7ab0 ("x86, amd: Avoid cache aliasing penalties on AMD family 15h")
> 
> This special case reduces the mmapped files entropy by eight.

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.

Btw., does this limitation affect both executable and non-executable 
mmap()s? Because data mmap()s don't need this I$ related workaround, 
right? So we could relax it for data-mmap()s?

Thanks,

	Ingo
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