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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: "joseph at codesourcery dot com" <joseph at codesourcery dot com>
- Cc: "schwab at suse dot de" <schwab at suse dot de>, "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 at anglin dot bell dot net" <dave at anglin dot bell dot net>, "wilson at tuliptree dot org" <wilson at tuliptree dot org>, Michael Eager <eager at eagercon dot com>
- Date: Wed, 20 Sep 2017 06:40:58 +0000
- Subject: Re: Enable no-exec stacks for more targets using the Linux kernel
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>On Tue, 19 Sep 2017, Andreas Schwab wrote:
> >On Sep 18 2017, Joseph Myers <joseph@codesourcery.com> wrote:
> >
> > Building glibc for many different configurations and running the
> > compilation parts of the testsuite runs into failures of the
> > elf/check-execstack test for hppa, ia64 and microblaze.
> >
>> ia64 is non-execstack by default, so it doesn't need any marking. The
>> same is true for every architecture that doesn't override
>> elf_read_implies_exec, which includes microblaze and hppa.
> Thanks for the explanation.
> 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?
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