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.
