linux-kernel - Re: [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU

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Date:   Mon, 10 Dec 2018 15:24:50 -0800
From:   Josh Triplett <josh@...htriplett.org>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-sgx@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Jethro Beekman <jethro@...tanix.com>,
        "Dr . Greg Wettstein" <greg@...ellic.com>
Subject: Re: [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU

On Mon, Dec 10, 2018 at 03:21:37PM -0800, Sean Christopherson wrote:
> At that point I realized it's a hell of a lot easier to simply provide
> an IOCTL via /dev/sgx that allows userspace to register a per-process
> ENCLU exception handler.  At a high level, the basic idea is the same
> as the vDSO approach: provide a hardcoded fixup handler for ENCLU and
> attempt to fixup select unhandled exceptions that occurred in user code.

So, on the one hand, this is *absolutely* much cleaner than the VDSO
approach. On the other hand, this is global process state and has some
of the same problems as a signal handler as a result.