On Mon, Nov 7, 2022 at 2:47 PM Edgecombe, Rick P <rick.p.edgecombe@xxxxxxxxx> wrote: > > On Mon, 2022-11-07 at 13:47 -0800, H.J. Lu wrote: > > On Mon, Nov 7, 2022 at 1:34 PM Edgecombe, Rick P > > <rick.p.edgecombe@xxxxxxxxx> wrote: > > > > > > On Mon, 2022-11-07 at 13:21 -0800, H.J. Lu wrote: > > > > > > Some applications and libraries are compiled with -fcf- > > > > > > protection, > > > > > > but > > > > > > they manipulate the stack in such a way that they aren't > > > > > > compatible > > > > > > with the shadow stack. However, if the build/test setup > > > > > > doesn't > > > > > > support > > > > > > shadow stack, it is impossible to validate. > > > > > > > > > > > > > > > > When we have everything in place, the problems would be much > > > > > more > > > > > obvious when distros started turning it on. But we can't turn > > > > > it on > > > > > as > > > > > > > > Not necessarily. The problem will show up only in a CET enabled > > > > environment since build/test setup may not be on a CET capable > > > > hardware. > > > > > > Well, I'm not sure of the details of distro testing, but there are > > > plenty of TGL and later systems out there today. With kernel > > > support, > > > I'm thinking these types of problems couldn't lurk for years like > > > they > > > have. > > > > If this is the case, we would have nothing to worry about since the > > CET > > enabled applications won't pass validation if they aren't CET > > compatible. > > Hmm, I think you couldn't have already forgotten the problem binaries > are already shipped... It should be OK since glibc doesn't support CET. > > > > > > > > > > > planned without breaking things for existing binaries. We can > > > > > have > > > > > both > > > > > by: > > > > > 1. Choosing a new bit, adding it to the tools, and never > > > > > supporting > > > > > the > > > > > old bit in glibc. > > > > > 2. Providing the option to have the kernel block the old bit, > > > > > so > > > > > upgraded users can decide what experience they would like. Then > > > > > distros > > > > > can find the problems and adjust their packages. I'm starting > > > > > to > > > > > think > > > > > a default off sysctl toggle might be better than a Kconfig. > > > > > 3. Any other ideas? > > > > > > > > Don't enable CET in glibc until we can validate CET > > > > functionality. > > > > > > Can you elaborate on what you mean by this? Not upstream glibc CET > > > support? Or have users not enable it? If the latter, how would they > > > know about all these problems. > > > > The current glibc doesn't support CET. To enable CET in an > > application, > > one should validate it together with the CET enabled glibc under the > > CET > > enabled kernel on a CET capable machine. > > Agreed that this is how it should have gone. > > > > > > > > > And what is wrong with the cleanest option, number 1? The ABI > > > document > > > can be updated. > > > > It doesn't help resolve any issues. > > Please read the coverletter if you are unsure of what issues this is > trying to address. I should have put more in the commit log. > > > -- H.J.
