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From:   Jethro Beekman <jethro@fortanix.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>
CC:     Dave Hansen <dave.hansen@linux.intel.com>,
        "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
        Florian Weimer <fweimer@redhat.com>,
        Linux API <linux-api@vger.kernel.org>,
        Jann Horn <jannh@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        X86 ML <x86@kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
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        "Ayoun, Serge" <serge.ayoun@intel.com>,
        "shay.katz-zamir@intel.com" <shay.katz-zamir@intel.com>,
        "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
Subject: Re: RFC: userspace exception fixups
Thread-Topic: RFC: userspace exception fixups
Thread-Index: AQHUcgvc1wPHkMTl1kOh3Odo0nI54qVVOPcAgAIcTACAAAkSAIAAEDkAgAEgLYCAAFYTgIAAf1EAgABqtgA=
Date:   Wed, 21 Nov 2018 05:17:32 +0000
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On 2018-11-21 04:25, Jarkko Sakkinen wrote:
> On Tue, Nov 20, 2018 at 07:19:37AM -0800, Andy Lutomirski wrote:
>> general by mucking with some regs and retrying -- that will infinite
>> loop and confuse everyone.  I'm not even 100% convinced that decoding
>> the insn stream is useful -- AEP can point to something that isn't
>> ENCLU.
>=20
> In my return-to-AEP approach to whole point was not to do any decoding
> but instead have something else always in the AEP handler than just
> ENCLU.
>=20
> No instruction decoding. No RIP manipulation.
>=20
>> IOW the kernel needs to know *when* to apply this special behavior.
>> Sadly there is no bit in the exception frame that says "came from
>> SGX".

Jarkko, can you please explain you solution in detail? The CPU receives=20
an exception. This will be handled by the kernel exception handler. What =

information does the kernel exception handler use to determine whether=20
to deliver the exception as a regular signal to the process, or whether=20
to set the special registers values for userspace and just continue=20
executing the process manually?

--
Jethro Beekman | Fortanix


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