On Mon, Apr 22, 2019 at 06:29:06PM -0700, Andy Lutomirski wrote: > What's not tested here is running this code with EFLAGS.TF set and > making sure that it unwinds correctly. Also, Jarkko, unless I missed > something, the vDSO extable code likely has a bug. If you run the > instruction right before ENCLU with EFLAGS.TF set, then do_debug() > will eat the SIGTRAP and skip to the exception handler. Similarly, if > you put an instruction breakpoint on ENCLU, it'll get skipped. Or is > the code actually correct and am I just remembering wrong? The code is indeed broken, and I don't see a sane way to make it not broken other than to never do vDSO fixup on #DB or #BP. But that's probably the right thing to do anyways since an attached debugger is likely the intended recipient the 99.9999999% of the time. The crux of the matter is that it's impossible to identify whether or not a #DB/#BP originated from within an enclave, e.g. an INT3 in an enclave will look identical to an INT3 at the AEP. Even if hardware provided a magic flag, #DB still has scenarios where the intended recipient is ambiguous, e.g. data breakpoint encountered in the enclave but on an address outside of the enclave, breakpoint encountered in the enclave and a code breakpoint on the AEP, etc...
