Re: prctl call wrongly succeeds on HPPA?

[Sam James <sam@gentoo.org>]

Helge Deller <deller@gmx.de> writes:

> On 11/3/23 13:53, Sam James wrote:
>> Sam James <sam@gentoo.org> writes:
>>> I recently hit an issue with systemd-254 which tries to use the new
>>> prctl(PR_SET_MDWE) for systemd's MemoryDenyWriteExecute functionality.
>
> Is this still a problem?

Yes. When I get time, I will play with Dave's changes to allow using
non-exeuctable stacks, but for now, it is broken until I can test these
(thanks dave for working on that, and helge for the kernel side).

>
>>> On HPPA, we still need executable stacks, so this option doesn't work
>>> and leads to a segfault on boot.
>
> For kernel we don't need it any longer.
> But there might be dependencies on glibc version and/or combination.
> So, I've currently lost overview if we still need executable stacks...
>

I don't remember which kernel version either.. I think it was last year
that you finished off all the DSO bits.

I had to configure binutils with --enable-default-execstack=no for it to
work in addition to Dave's GCC patches. But I did not test systemd yet...

(sorry, I know this is equally vague.)

>>> Should this call be succeeeding on HPPA, or should we reject it for
>>> now until we have things wired up?
>>>
>>> Reported to systemd at https://github.com/systemd/systemd/issues/29775.
>>
>> Lennart has made clear (and I don't think I disagree) that he considers
>> this squarely a kernel bug.
>
> I've read the various bug reports and looked at the kernel commits regarding, e.g.
>
> commit b507808ebce23561d4ff8c2aa1fb949fe402bc61
> Author: Joey Gouly <joey.gouly@arm.com>
> Date:   Thu Jan 19 16:03:43 2023 +0000
>
>     mm: implement memory-deny-write-execute as a prctl
>
> but what is prctl(PR_SET_MDWE, PR_MDWE*, 0, 0)... expected to return on parisc?
> EINVAL? ENOTSUP?

Maybe we can ask Joey or the ARM people what they expect the semantics
to be.

>
> Helge