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RE: Enable no-exec stacks for more targets using the Linux kernel
- From: Nagaraju Mekala <nmekala at xilinx dot com>
- To: Andreas Schwab <schwab at suse dot de>, Joseph Myers <joseph at codesourcery dot com>
- Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, "law at redhat dot com" <law at redhat dot com>, "dave dot anglin at bell dot net" <dave dot anglin at bell dot net>, "wilson at tuliptree dot org" <wilson at tuliptree dot org>, "eager at eagercon dot com" <eager at eagercon dot com>
- Date: Wed, 20 Sep 2017 06:55:28 +0000
- Subject: RE: Enable no-exec stacks for more targets using the Linux kernel
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> -----Original Message-----
> From: gcc-patches-owner@gcc.gnu.org [mailto:gcc-patches-
> owner@gcc.gnu.org] On Behalf Of Andreas Schwab
> Sent: Wednesday, September 20, 2017 12:19 PM
> To: Joseph Myers <joseph@codesourcery.com>
> Cc: gcc-patches@gcc.gnu.org; law@redhat.com; dave.anglin@bell.net;
> wilson@tuliptree.org; eager@eagercon.com
> Subject: Re: Enable no-exec stacks for more targets using the Linux kernel
>
> On Sep 19 2017, Joseph Myers <joseph@codesourcery.com> wrote:
>
> > I've sent a glibc patch
> > <https://sourceware.org/ml/libc-alpha/2017-09/msg00734.html>. I think
> > the key questions for architecture experts now are: on each of those
> > three architectures, do trampolines ever require executable stacks,
> > and, if they do, how does this work at present when the kernel
> > defaults to non-executable and my understanding at
> > <https://sourceware.org/ml/libc-alpha/2017-09/msg00747.html> would be
> > that glibc would only make thread stacks executable on those
> > architectures, not the main process stacks, and GCC will never
> > generate an explicit marker on those architectures to request an executable
> stack?
>
> For ia64 on linux there is EF_IA_64_LINUX_EXECUTABLE_STACK to request
> executable heap and stack. But since ia64 uses function descriptors,
> trampolines never need that.
>
> Andreas.
Sorry somehow mail thread was missed in my earlier mail.
Resending the same reply again:
Microblaze is a soft processor with many configuration options.
If we don't use the MMU, there is nothing preventing execution of code on the stack in the MicroBlaze architecture.
With the MMU, you have the option to make any page, including the stack pages, executable or not.
It is recommended to prevent execution on the stack by defining those pages as non-executable in the MMU.
In particular, trampolines would have to be possible to code without execution on the stack
Thanks,
Nagaraju
> --
> Andreas Schwab, SUSE Labs, schwab@suse.de GPG Key fingerprint = 0196
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