Bug#552688: Please decide how Debian should enable hardening build flags
Hi,
On Tue, 26 Jul 2011, Raphael Hertzog wrote:
> Assuming that all those improvements are done, the consensus was that
> it's fine for dpkg-buildflags to start emitting the hardening build
> flags by default. According to Ubuntu's experience only a few dozen of
> packages are broken by the presence of these flags and those packages
> should just be updated to use the new STRIP operation to drop the
> problematic flags. This could be dealt as part of a wheezy release goal.
I have prepared a branch that implements all this, that also includes
hardening build flags and that modify dpkg's debian/rules to actually
use dpkg-buildflags in the way we expect maintainers to use it.
See http://anonscm.debian.org/gitweb/?p=users/hertzog/dpkg.git;a=shortlog;h=refs/heads/pu/build-flags
You can grab it with "git clone git://git.debian.org/~hertzog/dpkg.git -b
pu/build-flags".
In the course of doing this I discovered that this won't have the
expected result:
---
export DEB_CFLAGS_MAINT_APPEND = -Wall
[...]
./configure $(shell dpkg-buildflags --export=configure)
---
Apparently make doesn't export the variables to the sub-shell
run in this way but only to shells run for commands in the various
targets. So instead I have to do it this way:
./configure $(shell DEB_CFLAGS_MAINT_APPEND="-Wall" dpkg-buildflags --export=configure)
One thing that is really not clear to me is how we should handle PIE.
It's not enabled by default by the gcc patch. This means that it's not
safe to enable it by default in dpkg-buildflags because we have no idea of
its impact. While all the other options have been well tested thanks to
Ubuntu, this one was not. Yet it seems that we should still aim to use it
by default at some point. How should we handle that transition?
The current implementation in my branch is that PIE is disabled by defaut
but if you set DEB_BUILD_HARDENING_PIE=1 then it will be used. This was
easily done on top of the compatibility layer with
hardening-includes/hardening-wrapper but I'm not convinced it's an
interface we want to use for this transition.
In that case, it means that we should rebuild the archive with PIE
enabled, see what breaks, report bugs and ask people to add
DEB_CFLAGS_MAINT_STRIP="-fPIE" DEB_LDFLAGS_MAINT_STRIP="-fPIE -pie"
where required. Once most packages have been fixed, we can add
PIE to the default flags. Does this sound reasonable?
Should we go further and provide centralized variables that can be used
to strip out the precise set of build flags that each hardening "feature"
adds? For reference /usr/share/hardening-includes/hardening.make does
provide such variables.
Cheers,
--
Raphaël Hertzog ◈ Debian Developer
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▶ http://RaphaelHertzog.fr (Français)
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