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Date: Mon, 11 Mar 2013 14:01:30 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Kees Cook <keescook@chromium.org>
Cc: Greg KH <gregkh@linuxfoundation.org>, Ben Hutchings <ben@decadent.org.uk>,
        luis.henriques@canonical.com, LKML <linux-kernel@vger.kernel.org>
Subject: Re: + signal-always-clear-sa_restorer-on-execve.patch added to -mm
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On Mon, 11 Mar 2013 13:37:53 -0700 Kees Cook <keescook@chromium.org> wrote:

> ...
>

(pop toasting undone)

> > Subject: signal: always clear sa_restorer on execve
> >
> > When the new signal handlers are set up, the location of sa_restorer is
> > not cleared, leaking a parent process's address space location to
> > children.  This allows for a potential bypass of the parent's ASLR by
> > examining the sa_restorer value returned when calling sigaction().
> >
> > Based on what should be considered "secret" about addresses, it only
> > matters across the exec not the fork (since the VMAs haven't changed until
> > the exec).  But since exec sets SIG_DFL and keeps sa_restorer, this is
> > where it should be fixed.
>
> A note for backporters: you'll likely want to change
> __ARCH_HAS_SA_RESTORER to SA_RESTORER, since the former was recently
> introduced. If not, this will apply but not actually do any good.

I added this to the changelog, but I fear people won't read it!  Is
there any clever way in which we can have one patch which will work OK
in both old and new kernels?  I can't think of one...