linux-kernel - Re: [PATCH v15 23/23] x86/sgx: Driver documentation

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Message-ID: <e7b4c432-7005-308c-4da0-a80e0d294244@intel.com>
Date:   Tue, 6 Nov 2018 08:45:37 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        linux-sgx@...r.kernel.org, sean.j.christopherson@...el.com,
        nhorman@...hat.com, npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...el.com,
        mark.shanahan@...el.com, andriy.shevchenko@...ux.intel.com,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v15 23/23] x86/sgx: Driver documentation

On 11/5/18 9:49 PM, Jarkko Sakkinen wrote:
> On Mon, Nov 05, 2018 at 12:27:11PM -0800, Dave Hansen wrote:
>> The ABI seems entirely undocumented and rather lightly designed, which
>> seems like something we should fix before this is merged.
> 
> ABI is documented in arch/x86/include/uapi/asm/sgx.h that from which the
> documentation is included to intel_sgx.rst. I'm not saying that there is
> no space refine it but it is neither undocumented.

I specifically mean the instruction flow around asynchronous exits or
explicit enclave exit calls via EEXIT.  Signals are part of the ABI but
go unmentioned in the documentation.

It's also worth noting that EENTER *can* act (from the kernel's
perspective) like an instruction that both jumps and sets a bunch of
registers (including %rsp).  It's certainly abnormal in that regard.

In fact, in the docs:

> +Enclave can only execute code inside the ELRANGE. Instructions that may cause
> +VMEXIT, IO instructions and instructions that require a privilege change are
> +prohibited inside the enclave. Interrupts and exceptions always cause enclave
> +to exit and jump to an address outside the enclave given when the enclave is
> +entered by using the leaf instruction ENCLS(EENTER).

it's probably a really good idea to explain that the address outside of
the enclave is enclave-provided, and is not, for instance, just the next
instruction after EENTER.

>> Also, for a feature as massive and complicated as this one, it seems
>> irresponsible to not have a selftest.  Is that not feasible for some reason?
> 
> I do have the in-kernel launch enclave stuff backed up here:
> 
> https://github.com/jsakkine-intel/sgx-le-host
> https://github.com/jsakkine-intel/sgx-le
> 
> This is about as simple as it gets without any type of run-time.

Does this code run when I type "make kselftest"?  If not, I think we
should rectify that.