linux-kernel - Re: RFC: userspace exception fixups

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Date:   Fri, 2 Nov 2018 17:05:25 +0000
From:   Jethro Beekman <jethro@...tanix.com>
To:     Andy Lutomirski <luto@...nel.org>
CC:     "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rich Felker <dalias@...c.org>, Jann Horn <jannh@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        Linux API <linux-api@...r.kernel.org>, X86 ML <x86@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "shay.katz-zamir@...el.com" <shay.katz-zamir@...el.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Carlos O'Donell <carlos@...hat.com>,
        "adhemerval.zanella@...aro.org" <adhemerval.zanella@...aro.org>
Subject: Re: RFC: userspace exception fixups

On 2018-11-02 10:01, Andy Lutomirski wrote:
> On Fri, Nov 2, 2018 at 9:56 AM Jethro Beekman <jethro@...tanix.com> wrote:
>>
>> On 2018-11-02 09:52, Sean Christopherson wrote:
>>> On Fri, Nov 02, 2018 at 04:37:10PM +0000, Jethro Beekman wrote:
>>>> On 2018-11-02 09:30, Sean Christopherson wrote:
>>>>> ... The intended convention for EENTER is to have an ENCLU at the AEX target ...
>>>>>
>>>>> ... to further enforce that the AEX target needs to be ENCLU.
>>>>
>>>> Some SGX runtimes may want to use a different AEX target.
>>>
>>> To what end?  Userspace gets no indication as to why the AEX occurred.
>>> And if exceptions are getting transfered to userspace the trampoline
>>> would effectively be handling only INTR, NMI, #MC and EPC #PF.
>>>
>>
>> Various reasons...
>>
>> Userspace may have established an exception handling convention with the
>> enclave (by setting TCS.NSSA > 1) and may want to call EENTER instead of
>> ERESUME.
>>
> 
> Ugh,
> 
> I sincerely hope that a future ISA extension lets the kernel return
> directly back to enclave mode so that AEX events become entirely
> invisible to user code.

Can you explain how this would work for things like #BR/#DE/#UD that 
need to be fixed up by code running in the enclave before it can be resumed?

-- 
Jethro Beekman | Fortanix


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