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Subject: Re: [PATCH v14 09/19] x86/mm: x86/sgx: Signal SEGV_SGXERR for #PFs w/ PF_SGX
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <20180927142158.GG8242@linux.intel.com>
Date:   Thu, 27 Sep 2018 07:41:00 -0700
Cc:     Dave Hansen <dave.hansen@intel.com>,
        "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
        Andrew Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        Platform Driver <platform-driver-x86@vger.kernel.org>,
        nhorman@redhat.com, npmccallum@redhat.com,
        "Ayoun, Serge" <serge.ayoun@intel.com>, shay.katz-zamir@intel.com,
        linux-sgx@vger.kernel.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        LKML <linux-kernel@vger.kernel.org>
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References: <20180925130845.9962-10-jarkko.sakkinen@linux.intel.com> <CALCETrVAhiwv+g5fzVO3ZSHZgcQKbeeG8r3HUcXO9k7Gi94NdQ@mail.gmail.com> <20180926173516.GA10920@linux.intel.com> <2D60780F-ADB4-48A4-AB74-15683493D369@amacapital.net> <9835e288-ba98-2f9e-ac73-504db9512bb9@intel.com> <20180926204400.GA11446@linux.intel.com> <b7e14c6e-fc05-93fa-eef9-5e3f06ab4729@intel.com> <CALCETrXByb2UVuZ6AXUeOd8y90NAikbZuvdN3wf_TjHZ+CxNhA@mail.gmail.com> <992b1d6d-cc0f-776f-d938-2a1f7cad52c8@intel.com> <CALCETrXyjRh1sBk1V21iTtjdhiWGCYsHnUNktkJC5xFiZy6c9A@mail.gmail.com> <20180927142158.GG8242@linux.intel.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Sep 27, 2018, at 7:21 AM, Jarkko Sakkinen <jarkko.sakkinen@linux.intel.=
com> wrote:
>=20
>> On Wed, Sep 26, 2018 at 03:37:45PM -0700, Andy Lutomirski wrote:
>> Yeah.  Maybe like this: > > xorl %eax,%eax > eenter_insn:
>> ENCLU[whatever]
>> eenter_landing_pad:
>> ret
>>=20
>> And the kernel would use the existing vdso2c vdso-symbol-finding
>> mechanism to do the fixup.
>>=20
>>>=20
>>> How would a syscall work, though?  I assume we can't just enter the
>>> enclave from ring0.
>>=20
>> My understanding of how AEX works is a bit vague, but maybe a syscall
>> could reuse the mechanism?  The vDSO approach seems considerably
>> simpler.
>>=20
>> We do need to make sure that a fault that happens on or after return
>> from an AEX event does the right thing.  But I'm still vague on how
>> that works, sigh.
>>=20
>> --Andy
>=20
> Returning from AEX does not differ from any other memory access event so
> AFAIK it should be handled right with the proposed solution already.
> For convenience I think we could have a fixed trampoline for AEX e.g.
> this how it is implemented in the open source LE that I did:
>=20
> sgx_get_token:
>    push    %rbx
>    mov    $0x02, %rax
>    mov    %rsi, %rbx
>    mov    %rdx, %rsi
>    mov    $sgx_async_exit, %rcx
> sgx_async_exit:
>    ENCLU
>    pop    %rbx
>    ret
>=20
> BTW, if I converted the in-kernel LE as a standalone test program, would
> that be useful for basic testing of the series?
>=20
>=20

Definitely. Especially if you stick it in selftests/x86 and make it exit cle=
anly (error code 0) on unsupported hardware.=