Re: [PATCH v26 0/9] Control-flow Enforcement: Indirect Branch Tracking

[Andy Lutomirski]

On Wed, Apr 28, 2021 at 7:57 AM H.J. Lu <hjl.tools@xxxxxxxxx> wrote:
>
> On Wed, Apr 28, 2021 at 7:52 AM Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> >
> > On Wed, Apr 28, 2021 at 7:48 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
> > >
> > > From: Yu-cheng Yu
> > > > Sent: 27 April 2021 21:47
> > > >
> > > > Control-flow Enforcement (CET) is a new Intel processor feature that blocks
> > > > return/jump-oriented programming attacks.  Details are in "Intel 64 and
> > > > IA-32 Architectures Software Developer's Manual" [1].
> > > ...
> > >
> > > Does this feature require that 'binary blobs' for out of tree drivers
> > > be compiled by a version of gcc that adds the ENDBRA instructions?
> > >
> > > If enabled for userspace, what happens if an old .so is dynamically
> > > loaded?
>
> CET will be disabled by ld.so in this case.

What if a program starts a thread and then dlopens a legacy .so?

>
> > > Or do all userspace programs and libraries have to have been compiled
> > > with the ENDBRA instructions?
>
> Correct.  ld and ld.so check this.
>
> > If you believe that the userspace tooling for the legacy IBT table
> > actually works, then it should just work.  Yu-cheng, etc: how well
> > tested is it?
> >
>
> Legacy IBT bitmap isn't unused since it doesn't cover legacy codes
> generated by legacy JITs.
>

How does ld.so decide whether a legacy JIT is in use?