linux-kernel - Re: RFC: userspace exception fixups

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Message-ID: <4171a890-12d9-8a1c-22da-e53434c1f840@fortanix.com>
Date:   Wed, 7 Nov 2018 06:47:08 +0000
From:   Jethro Beekman <jethro@...tanix.com>
To:     Andy Lutomirski <luto@...nel.org>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>
CC:     Dave Hansen <dave.hansen@...el.com>, Jann Horn <jannh@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rich Felker <dalias@...c.org>,
        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 2018-11-07 02:17, Andy Lutomirski wrote:
> On Tue, Nov 6, 2018 at 4:02 PM Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
>>
>> /*
>>   * EEXIT or EENTER faulted.  In the latter case, %RAX already holds some
>>   * fault indicator, e.g. -EFAULT.
>>   */
>> eexit_or_eenter_fault:
>>      ret
> 
> But userspace wants to know whether it was a fault or not.  So I think
> we either need two landing pads or we need to hijack a flag bit (are
> there any known-zeroed flag bits after EEXIT?) to say whether it was a
> fault.  And, if it was a fault, we should give the vector, the
> sanitized error code, and possibly CR2.

On AEX, %rax will contain ENCLU_LEAF_ERESUME (0x3). On EEXIT, %rax will 
contain ENCLU_LEAF_EEXIT (0x4).

--
Jethro Beekman | Fortanix


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