On Mon, Mar 9, 2020 at 1:16 PM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > > > > On Mar 9, 2020, at 12:50 PM, H.J. Lu <hjl.tools@xxxxxxxxx> wrote: > > > > On Mon, Mar 9, 2020 at 12:35 PM Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > >> > >>> On 3/9/20 12:27 PM, Yu-cheng Yu wrote: > >>> On Mon, 2020-03-09 at 10:21 -0700, Dave Hansen wrote: > >>>> On 3/9/20 10:00 AM, Yu-cheng Yu wrote: > >>>>> On Wed, 2020-02-26 at 09:57 -0800, Dave Hansen wrote>>>>> +Note: > >>>>>>> + There is no CET-enabling arch_prctl function. By design, CET is > >>>>>>> + enabled automatically if the binary and the system can support it. > >>>>>> > >>>>>> This is kinda interesting. It means that a JIT couldn't choose to > >>>>>> protect the code it generates and have different rules from itself? > >>>>> > >>>>> JIT needs to be updated for CET first. Once that is done, it runs with CET > >>>>> enabled. It can use the NOTRACK prefix, for example. > >>>> > >>>> Am I missing something? > >>>> > >>>> What's the direct connection between shadow stacks and Indirect Branch > >>>> Tracking other than Intel marketing umbrellas? > >>> > >>> What I meant is that JIT code needs to be updated first; if it skips RETs, > >>> it needs to unwind the stack, and if it does indirect JMPs somewhere it > >>> needs to fix up the branch target or use NOTRACK. > >> > >> I'm totally lost. I think we have very different models of how a JIT > >> might generate and run code. > >> > >> I can totally see a scenario where a JIT goes and generates a bunch of > >> code, then forks a new thread to go run that code. The control flow of > >> the JIT thread itself *NEVER* interacts with the control flow of the > >> program it writes. They never share a stack and nothing ever jumps or > >> rets between the two worlds. > >> > >> Does anything actually do that? I've got no idea. But, I can clearly > >> see a world where the entirety of Chrome and Firefox and the entire rust > >> runtime might not be fully recompiled and CET-enabled for a while. But, > >> we still want the JIT-generated code to be CET-protected since it has > >> the most exposed attack surface. > >> > >> I don't think that's too far-fetched. > > > > CET support is all or nothing. You can mix and match, but you will get > > no CET protection, similar to NX feature. > > > > Can you explain? I was talking about creating a program from mixed object files with and without CET marker. > If a program with the magic ELF CET flags missing can’t make a thread with IBT and/or SHSTK enabled, then I think we’ve made an error and should fix it. > A non-CET program can start a CET program and vice versa. -- H.J.
