On Thu, Jun 27, 2019 at 01:32:58PM -0700, Xing, Cedric wrote: > Just a reminder that #DB/#BP shall be treated differently because they are > used by debuggers. So instead of branching to the fixup address, the kernel > shall just signal the process. More importantly, doing fixup on #DB and #BP simply doesn't work. On Tue, Apr 23, 2019 at 11:59:37AM -0700, Sean Christopherson wrote: > 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...
