linux-kernel - Re: [PATCH v14 19/19] x86/sgx: Driver documentation

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Message-ID: <alpine.DEB.2.21.1810180205490.5022@jsakkine-mobl1>
Date:   Thu, 18 Oct 2018 02:45:27 +0300 (EEST)
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Pavel Machek <pavel@....cz>
cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org, dave.hansen@...el.com,
        sean.j.christopherson@...el.com, nhorman@...hat.com,
        npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, linux-sgx@...r.kernel.org,
        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 v14 19/19] x86/sgx: Driver documentation

On Mon, 15 Oct 2018, Pavel Machek wrote:
> On Tue 2018-09-25 16:06:56, Jarkko Sakkinen wrote:
>> +Intel(R) SGX is a set of CPU instructions that can be used by applications to
>> +set aside private regions of code and data. The code outside the enclave is
>> +disallowed to access the memory inside the enclave by the CPU access control.
>> +In a way you can think that SGX provides inverted sandbox. It protects the
>> +application from a malicious host.
>
> Well, recently hardware had some problems keeping its
> promises. So... what about rowhammer, meltdown and spectre?

Doesn't hardware always have this problem over time?

> Which ones apply, which ones do not, and on what cpu generations?

Definitely should be refined.

Meltdowns approach AFAIK does not work because reads outside the enclave
will always have a predefined value (-1) but only if the page is present,
which was later exploited in the Foreshadow attack.

> Encryption, that sounds nice, but it is hard to do right. If SGX
> protected code changes single bit in its memory, how many bits will be
> changed in physical RAM?

512-bit blocks and merkle tree based mac. It is pretty well documented
in https://eprint.iacr.org/2016/204.pdf. I'll take not to myself to add
this to the references.

Thanks for the feedback. The ocumentation is hard to drive forward w/o it.

/Jarkko