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Date: Wed, 21 Jun 2017 23:29:56 +0200
From: "PaX Team" <>
To:, Agostino Sarubbo <>
Subject: Re: Qualys Security Advisory - The Stack Clash

On 21 Jun 2017 at 10:22, Jeff Law wrote:

> On 06/21/2017 04:46 AM, Agostino Sarubbo wrote:
> > On Monday 19 June 2017 08:28:43 Qualys Security Advisory wrote:
> >> III. Solutions
> >> - Recompile all userland code (, libraries, binaries) with GCC's
> >>   "-fstack-check" option, which prevents the stack-pointer from moving
> >>   into another memory region without accessing the stack guard-page (it
> >>   writes one word to every 4KB page allocated on the stack).
> > 
> > For the record, Gentoo Hardened enables by default -fstack-check=specific
> And if you were to look at the generated code, you'll see that it
> happily skips 2-3 pages of probes in prologues as well as within alloca
> spaces.  It's a false sense of security.

Gentoo Hardened uses the grsecurity kernel which enforces a 64kB heap-stack
gap by default (it's also user adjustable). are you saying that the gcc
probes are not sufficient to prevent jumping over that range?

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