> 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? 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. > -- > H.J.
