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

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Date:   Tue, 2 Oct 2018 03:07:25 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrew Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        nhorman@...hat.com, npmccallum@...hat.com,
        "Ayoun, Serge" <serge.ayoun@...el.com>, shay.katz-zamir@...el.com,
        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 Mon, Oct 01, 2018 at 07:29:03AM -0700, Sean Christopherson wrote:
> On Wed, 2018-09-26 at 14:15 -0700, Andy Lutomirski wrote:
> > runs an enclave an returns an error code, and rig up the #PF handler
> > to check if the error happened in the vDSO entry and fix it up rather
> > than sending a signal?
> 
> 
> If we want to avoid having to install a signal handler then I'm pretty
> sure we'd need to fixup all #GPs and "bad access" #PFs that occur on
> EENTER or in the enclave, not just PF_SGX faults.  SGX1 hardware takes
> a #GP instead of a #PF on EPCM faults, and SGX2 hardware allows enclaves
> to allocate/free/adjust EPC pages at runtime, e.g. an enclave runtime
> might want to intercept #PFs from within the enclave so that the enclave
> can dynamically grow its stack.

If I've understood Andy's proposal correctly, the run-time would get the
same information as with a signal. The delivery path for this
information would be just different.

/Jarkko