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From:	John Selbie <jselbie AT gmail DOT com>
Date:	Mon, 2 Mar 2020 20:53:06 -0800
Message-ID:	<CAJn6YFBcmnkZ_hGY_OJPguT+m-4UG_2oTCuMCPTD2GVW3JFbDg@mail.gmail.com>
Subject:	Re: ASLR revisited
To:	cygwin AT cygwin DOT com
X-IsSubscribed:	yes

And I just discovered that recompiling with this added to the g++ command
line:

 -Xlinker --dynamicbase

Seems to work. Or at the least, triggers the process to show up in Process
Explorer as ASLR?

Good idea to continue with this?



On Mon, Mar 2, 2020 at 8:26 PM John Selbie <jselbie AT gmail DOT com> wrote:

> For my open source project, I publish source code for Unix written in C++.
> And as a convenience, I publish Win32 binaries compiled with Cygwin's g++
> build. I bundled the compiled EXE along with the dependent Cygwin DLLs
> (cygcrypto, cyggcc, cycstdc++, cygwin1, and cygz.dll).
>
> Someone rang me up today and said, "We're about to go live with your
> pre-compiled binaries for Windows, but our compliance testing detected your
> code isn't using ASLR (Address Space Layout Randomization).  Can you fix?"
>
> A quick internet search reveals that Cygwin has a compatibility issue with
> ASRL. Process Explorer from sysinternals.com reveals that the process
> runs without ASLR.
>
> I tried using the Windows 10 Exploit Protection Panel - and specifying an
> exception for this executable to have mandatory ASLR. That results in the
> code no longer running.  Although the alternate option of "Botton-up ASLR"
> did allow the code to run, but Process Explorer still doesn't show it
> running with ASLR.
>
> Is there a workaround for allowing Cygwin code to have ASLR?  I don't need
> the fork() function.
>
> Thanks,
> jrs
>

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