linux-kernel - Re: [PATCH 05/25] x86/sgx: Introduce runtime protection bits

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Message-ID: <e2d675f7-319b-4816-ad5e-4154cbf69f2b@intel.com>
Date:   Fri, 14 Jan 2022 16:41:59 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
CC:     Nathaniel McCallum <nathaniel@...fian.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        <dave.hansen@...ux.intel.com>, <tglx@...utronix.de>,
        <bp@...en8.de>, <mingo@...hat.com>, <linux-sgx@...r.kernel.org>,
        <x86@...nel.org>, <seanjc@...gle.com>, <kai.huang@...el.com>,
        <cathy.zhang@...el.com>, <cedric.xing@...el.com>,
        <haitao.huang@...el.com>, <mark.shanahan@...el.com>,
        <hpa@...or.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 05/25] x86/sgx: Introduce runtime protection bits

Hi Jarkko,

On 1/14/2022 4:27 PM, Jarkko Sakkinen wrote:
> On Fri, Jan 14, 2022 at 04:01:33PM -0800, Reinette Chatre wrote:
>> Hi Jarkko,
>>
>> On 1/14/2022 3:15 PM, Jarkko Sakkinen wrote:
>>> On Fri, Jan 14, 2022 at 03:05:21PM -0800, Reinette Chatre wrote:
>>>> Hi Jarkko,
>>>
>>> How enclave can check a page range that EPCM has the expected permissions?
>>
>> Only way to change EPCM permissions from outside enclave is to run ENCLS[EMODPR]
>> that needs to be accepted from within the enclave via ENCLU[EACCEPT]. At that
>> time the enclave provides the expected permissions and that will fail
>> if there is a mismatch with the EPCM permissions (SGX_PAGE_ATTRIBUTES_MISMATCH).
> 
> This is a very valid point but that does make the introspection possible
> only at the time of EACCEPT.
> 
> It does not give tools for enclave to make sure that EMODPR-ETRACK dance
> was ever exercised.

Could you please elaborate? EACCEPT is available to the enclave as a tool
and it would fail if ETRACK was not completed (error SGX_NOT_TRACKED).

Here is the relevant snippet from the SDM from the section where it
describes EACCEPT:

IF (Tracking not correct)
    THEN
        RFLAGS.ZF := 1;
        RAX := SGX_NOT_TRACKED;
        GOTO DONE;
FI;

Reinette