Re: RFC: userspace exception fixups

[Jarkko Sakkinen]

On Thu, 1 Nov 2018, Florian Weimer wrote:
> * Andy Lutomirski:
>
> > The basic idea would be to allow libc, or maybe even any library, to
> > register a handler that gets a chance to act on an exception caused by
> > a user instruction before a signal is delivered.  As a straw-man
> > example for how this could work, there could be a new syscall:
> >
> > long register_exception_handler(void (*handler)(int, siginfo_t *, void *));
> >
> > If a handler is registered, then, if a synchronous exception happens
> > (page fault, etc), the kernel would set up an exception frame as usual
> > but, rather than checking for signal handlers, it would just call the
> > registered handler.  That handler is expected to either handle the
> > exception entirely on its own or to call one of two new syscalls to
> > ask for normal signal delivery or to ask to retry the faulting
> > instruction.
>
> Would the exception handler be a per-thread resource?

For SGX purposes it would *need* to be per-thread resource so that the
run-time (not just Intel but any user space support code for SGX) is
able to act on thread that caused this exception inside the enclave.

/Jarkko