linux-kernel - Re: [PATCH v14 09/19] x86/mm: x86/sgx: Signal SEGV_SGXERR for #PFs w/ PF

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Date:   Thu, 1 Nov 2018 19:44:27 +0200 (EET)
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Andy Lutomirski <luto@...capital.net>,
        Andrew Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.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>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 09/19] x86/mm: x86/sgx: Signal SEGV_SGXERR for #PFs
 w/ PF_SGX



On Thu, 1 Nov 2018, Jarkko Sakkinen wrote:

> On Wed, 31 Oct 2018, Sean Christopherson wrote:
>> On Mon, Oct 01, 2018 at 03:03:30PM -0700, Dave Hansen wrote:
>>> On 10/01/2018 02:42 PM, Jethro Beekman wrote:
>>>> 
>>>> 1) Even though the vDSO function exists, userspace may still call
>>>> `ENCLU[EENTER]` manually, so the fault handling as described in the
>>>> current patch should also be maintained.
>>> 
>>> Why?
>> 
>> Circling back to this question, what if we take the easy way out and
>> simply signal SIGSEGV without an SGX-specific code?  I.e. treat #PF
>> with X86_PF_SGX as an access error, no more no less.  That should be
>> sufficient for userspace to function, albeit with a little more effort,
>> but presumably no more than would be needed to run on SGX1 hardware.
>> 
>> AFAIK there isn't a way to prevent userspace from manually invoking
>> EENTER, short of doing some really nasty text poking or PTE swizzling.
>> We could declare using EENTER as unsupported, but that seems like
>> cutting off the nose to spite the face.  Supporting userspace EENTER
>> in a limited capacity would allow people to do whatever crazy tricks
>> they're wont to do without having to deal with absurd requests for
>> the vDSO interface.
>> 
>> If we go this route we could also add the vDSO stuff after basic SGX
>> support is in mainline, obviously with approval from the powers that
>> be.
>> 
>
> Yeah, this would give stable behavior when vDSO functions are not
> available.
>
> Here's a question: if we implement this behavior, could be upstream
> series without vDSO's first and after those changes have been landed
> we would continue with the vDSO's?

Right, it was in your last paragraph, sorry. Yeah, I fully support this 
idea. It will be easier also to work on the vDSO's once we have something
landed (instead of working on a moving platform).

/Jarkko