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Date:   Thu, 1 Nov 2018 21:00:38 +0200 (EET)
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Florian Weimer <fweimer@redhat.com>
cc:     Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
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Subject: Re: RFC: userspace exception fixups
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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