Mailing List Archive

"Andreas K. Huettel" <dilfridge@gentoo.org> writes:

> Hi all,
>
> the 23.0 profiles are ready for testing, including stage downloads,
> binary packages, and update instructions for existing installations,
> for all arches.
>
> [...]
>
> Note 2: While there are 23.0 split-usr profiles, the *stage* downloads
> are *all* of the merged-usr type. Why? Not because I'm a big fan of that,
> but because we should try to unify and standardize a bit again - to
> avoid too many different build configurations leading to too many Heisenbugs.

I don't think this is a good idea.

We've promised people that they can keep unmerged-usr if they want, but
not having stages means new installs aren't doable, and it also makes
testing a pain because you can't easily unmerge.

You can easily merge, but you can't easily unmerge.

What you can do is provide a limited number of non-merged-usr variants
given it's just about saving people rebuilds.

(I also think it's the wrong way to do such a change anyway - the releng
part should be last after decision-making, not first.)

> [...]
> Cheers & have fun,

thanks,
sam

> > Note 2: While there are 23.0 split-usr profiles, the *stage* downloads
> > are *all* of the merged-usr type. Why? Not because I'm a big fan of that,
> > but because we should try to unify and standardize a bit again - to
> > avoid too many different build configurations leading to too many Heisenbugs.
>
> I don't think this is a good idea.
>
> We've promised people that they can keep unmerged-usr if they want,

And they can.

[.However, I don't see the point for it. Apart from ideological considerations,
there is no obvious advantage to the split-usr layout anymore.]

> but not having stages means new installs aren't doable,

Yes.

> and it also makes testing a pain because you can't easily unmerge.
> You can easily merge, but you can't easily unmerge.

That is the imho more important and valid point, maintaining the remaining
split-usr installs will get harder.

> What you can do is provide a limited number of non-merged-usr variants
> given it's just about saving people rebuilds.

For amd64 and arm64 that's doable (since builds are cheap there).
I would very much discourage using these variants for new installs though.

[.And yes I would prefer to deprecate the split-usr profiles and remove them
at some point in the not-so-far future. That is however a topic that needs
separate debate.]

> (I also think it's the wrong way to do such a change anyway - the releng
> part should be last after decision-making, not first.)

The decision where this is going has been made long ago... just not by us
because we've been lagging behind. But I get what you mean.


--
Andreas K. H?ttel
dilfridge@gentoo.org
Gentoo Linux developer
(council, comrel, toolchain, base-system, perl, libreoffice)
https://wiki.gentoo.org/wiki/User:Dilfridge

Andreas K. Huettel posted on Fri, 15 Mar 2024 19:12:54 +0100 as excerpted:

> Note 3: amd64 now has CET turned on by default.
> https://docs.kernel.org/next/x86/shstk.html If you have already used the
> unannounced 23.0 profiles, you should wipe your package cache and emerge
> -ev world now.

There's not much about CET in any of the links. While the kernel.org link
describes what it does (in a line, "yese": yet another security
enhancement) a bit, it doesn't say how to actually find whether your
hardware supports it, and the gentoo wiki and bug links say even less --
in particular, unless I missed it, the changes and update instructions
links don't appear to mention CET or shadow-stacks AT ALL.

What I ended up doing here after some DDG googling, was emerging cpuid,
then doing:

$$ cpuid -1 | grep -i 'cet\|shadow'
CET_SS: CET shadow stack = false
CET_IBT: CET indirect branch tracking = false
CET_U user state = false
CET_S supervisor state = false
supervisor shadow stack = false

With all of those false it would seem CET can't work here in any case so
there's no point rebuilding again, which is what I already suspected but
wanted to /know/. (I've been on a 23.0 merged-usr profile[1] for some
time now as I already had much of what it does already enabled before the
new profiles were announced here, so it /would/ be "rebuilding again" to
get that, but as it seems it won't do anything useful anyway...)

Clearer instructions for finding that out (and preferably what actually
has to be true, I still don't know that for sure) so others don't have to
google it, could be useful.

---
[1] Already on a merged-usr profile: Of course including developing an
auto-applied-on-update patch to do s:[[ ! -h "${EROOT%/}/bin" ]]:false: to
the profile bashrc after that test was added, because I am indeed usr-
merged (on systemd) here but that test fails because the operating symlink
is /usr -> . instead, aka reverse-usrmerge. Tho making the canonical
path /realbin and doing /bin -> /realbin would appear to satisfy the test
too, and would allow me to avoid patching the profile bashrc, but at least
here, having /bin be the system's real bin location is part of the _point_
of a reverse-usrmerge.

--
Duncan - List replies preferred. No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master." Richard Stallman

Am Samstag, 16. M?rz 2024, 13:12:04 CET schrieb Duncan:
> Andreas K. Huettel posted on Fri, 15 Mar 2024 19:12:54 +0100 as excerpted:
>
> > Note 3: amd64 now has CET turned on by default.
> > https://docs.kernel.org/next/x86/shstk.html If you have already used the
> > unannounced 23.0 profiles, you should wipe your package cache and emerge
> > -ev world now.
>
> There's not much about CET in any of the links. While the kernel.org link
> describes what it does (in a line, "yese": yet another security
> enhancement) a bit, it doesn't say how to actually find whether your
> hardware supports it, and the gentoo wiki and bug links say even less --
> in particular, unless I missed it, the changes and update instructions
> links don't appear to mention CET or shadow-stacks AT ALL.

That's because it was a last-minute addition, and not particularly well
thought through. :|

Ignore Note 3. The part about emerge -ev world is just plain wrong for now.

--
Andreas K. H?ttel
dilfridge@gentoo.org
Gentoo Linux developer
(council, comrel, toolchain, base-system, perl, libreoffice)
https://wiki.gentoo.org/wiki/User:Dilfridge