linux-kernel - Re: RFC: userspace exception fixups

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Message-ID: <20181126220627.GD868@linux.intel.com>
Date:   Mon, 26 Nov 2018 14:06:27 -0800
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Jethro Beekman <jethro@...tanix.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        Linux API <linux-api@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        X86 ML <x86@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rich Felker <dalias@...c.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>
Subject: Re: RFC: userspace exception fixups

On Mon, Nov 26, 2018 at 06:35:34AM -0800, Sean Christopherson wrote:
> And how would you determine the #UD is related to SGX?  Hardware doesn't
> provide any indication that a #UD (or any other fault) is related to SGX
> or occurred in an enclave.  The only fault that is special-cased in a
> non-virtualized environment is #PF signaled by the EPCM, which gets the
> PF_SGX bit set in the error code.

Could you not detect #UD from address where it happened? Kernel knows
where enclaves are mapped. BTW, how does Intel run-time emulate opcodes
currently?

Anyway, I've fully discarded the whole idea because implementing single
stepping w/o well defined AEP handler is nasty. I think vDSO's are the
only viable path that at least I'm aware off...

/Jarkko