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. -- H.J.
