PIE/PIC support on base

[Warner Losh]

On Oct 17, 2014, at 2:05 AM, Shawn Webb <lattera at gmail.com> wrote:

> On Fri, Oct 17, 2014 at 3:53 AM, Jeremie Le Hen <jlh at freebsd.org> wrote:
> 
>> On Fri, Oct 17, 2014 at 12:15 AM, Shawn Webb <lattera at gmail.com> wrote:
>>> 
>>> 
>>> On Thu, Oct 16, 2014 at 5:59 PM, Jeremie Le Hen <jlh at freebsd.org> wrote:
>>>> 
>>>> On Thu, Oct 16, 2014 at 8:21 PM, David Carlier
>>>> <david.carlier at hardenedbsd.org> wrote:
>>>>> 
>>>>> I chose the "atomic" approach, at the moment very few binaries are
>>>>> concerned at the moment. So I applied INCLUDE_PIC_ARCHIVE in the
>> needed
>>>>> libraries plus created WITH_PIE which add fPIE/fpie -pie flags only if
>>>>> you
>>>>> include <bsd.prog.pie.mk> (which include <bsd.prog.mk>...) otherwise
>>>>> other
>>>>> binaries include <bsd.prog.mk> as usual hence does not apply. Look
>>>>> reasonable approach ?
>>>> 
>>>> I think I understand what you mean.  But I think PIE is commonplace
>>>> nowadays and I don't understand what you win by not enabling it for
>>>> the whole system.  Is it a performance concern?  Is it to preserve
>>>> conservative minds from to much change? :)
>>> 
>>> 
>>> Looping in Kostik, Bryan Drewery, the PaX team, Hunger, and Sean Bruno.
>>> 
>>> On i386, there is a performance cost due to not having an extra register
>>> available for the relocation work that has to happen. PIE doesn't carry
>> much
>>> of a performance penalty on amd64, though it still does carry some on
>> first
>>> resolution of functions (due to the extra relocation step the RTLD has to
>>> worry about). On amd64, after symbol resolution has taken place, there
>> is no
>>> further performance penalty due to amd64 having an extra register to use
>> for
>>> PIE/PIC. I'm unsure what, if any, performance penalty PIE carries on ARM,
>>> AArch64, and sparc64.
>>> 
>>> Certain folk would prefer to see PIE enabled only in certain
>> applications.
>>> /bin/ls can't really make much use of PIE. But sshd can. I personally
>> would
>>> like to see all of base's applications compiled as PIEs, but that's a
>> long
>>> ways off. It took OpenBSD several years to accomplish that. Having
>> certain
>>> high-visibility applications (like sshd, inetd, etc) is a great start.
>>> Providing a framework for application developers to opt their application
>>> into PIE is another great start.
>>> 
>>> Those are my two cents.
>> 
>> OK.  As long as i386 is still an important architecture, it can make
>> sense to enable this on a per-binary basis if we don't want to have a
>> discrepancy between archs. Also I buy your argument on /bin/ls but I
>> was challenging to enable for the whole system because I wonder if
>> there aren't some unexpected attack surfaces, besides the obvious ones
>> (servers).
>> 
>> Do you know what took so much time to OpenBSD?
> 
> 
> In a private conversation with Theo, I realized that my recollection of the
> time it took OpenBSD to compile all of base as PIEs was wrong. Quoting him:
> 
> "It took 5 people approximately 3 months to debug it, activate it, and
> start shipping it the next release.  That was on amd64, for all
> dynamically linked binaries, except one (a gcc bug took some time to
> find).  The next architectures followed about 1 or 2 per 6-month
> release."
> 
> Given that only one person has worked on this in the past (me) and now the
> task has been delegated to another (David Carlier), I think we're doing
> okay on our end. There's a lot of moving parts, and neither of us fully
> understand all of them completely. We're working on it in HardenedBSD, in
> the hardened/current/pie branch.
> 
> I'm thinking we might try for a WITH_PIE knob (and *not* use USE_PIE) and
> have certain high-profile applications opt-in to PIE until we work out all
> the details for everything en masse. Baptiste did bring up a good point
> with INTERNALLIB and I'm unsure of how we should handle that.

WITH_PIE or WITHOUT_PIE controls, on a global basis, via the MK_PIE
variable, whether or not the user wants to turn on this feature for those
program that can do PIE. Designating which programs do, or don’t,
use PIE simply must be done with a different variable. I posted a bit of a
rant about the current state of things that suggested a couple of
alternatives as well as giving some history as to why some options
aren’t to be used and the history behind some of my reactions. :)

For this reason, I think WITH_PIE, as I understand your proposal,
likely isn’t a good fit with other WITH_xxx variables used in the src
tree today.

Warner
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