Re: F45 Change Proposal: Enable Shadow Stack by Default on x86_64 (system-wide)

On Fri, Jul 03, 2026 at 01:39:07PM +0200, Florian Weimer wrote:
> * Zbigniew Jędrzejewski-Szmek:
> 
> > On Wed, Jul 01, 2026 at 04:12:03PM -0400, Neal Gompa wrote:
> >> On Wed, Jul 1, 2026 at 3:59 PM Zbigniew Jędrzejewski-Szmek
> >> <[email protected]> wrote:
> >> >
> >> > > Wiki - https://fedoraproject.org/wiki/Changes/ShadowStack
> >> > > # The `dlopen`ed library is compiled with Shadow Stack support enabled.
> >> > > # The application opts out of Shadow Stack support using glibc's
> >> > > System-Wide Tunables feature. For example, a package named `app`
> >> > > providing `/usr/bin/app` would install `/etc/tunables.conf.d/app.conf`
> >> >
> >> > Please, please, please, make that /usr/lib/tunables.conf.d/app.conf
> >> > by default. As described below, this is clearly something that is
> >> > part of the rpm and not "local configuration".
> >> >
> >> 
> >> I don't think this path exists. That's a glibc thing, I think, and the
> >> doc about it doesn't indicate any hermetic /usr support.
> >> 
> >> https://sourceware.org/git/?p=glibc.git;a=blobdiff;f=manual/tunables.texi;h=828c68151ad887550430605f007e289b5235f110;hp=e1d9fbae9cebe961fe45203251a761c3323a9917;hb=fae194043a099d45c044c883467c934153ecc51f;hpb=fcea66cd4685f9f3719e09cac52c73b9ece4bade
> >
> > Hmm, lack of support for the /usr-/etc split in new code in 2026
> > is … disappointing.
> 
> We can still change it.  I suggested that we re-use /etc/ld.so.conf for
> the tunables settings.  Then
> 
>   Bug 2440274 - Source ld.so configs drop-ins from /usr/lib
>   <https://bugzilla.redhat.com/show_bug.cgi?id=2440274>
> 
> would cover everything.  But it was a minority viewpoint at the time of
> patch review.

I don't have a strong opinion whether ld.so.conf and tunables.conf should
be separate… But I'll say that when I first saw '/etc/tunables.d', I
had the thought that the name is quite generic. Reusing /etc/ld.so.conf
for the tunables would have the advantage that people would immediately
know that it is about the linker…

Zbyszek
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