linux-kernel - Re: [PATCH V4 00/31] x86/sgx and selftests/sgx: Support SGX2

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Date:   Mon, 25 Apr 2022 16:56:03 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     "Dhanraj, Vijay" <vijay.dhanraj@...el.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
CC:     "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "bp@...en8.de" <bp@...en8.de>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Shanahan, Mark" <mark.shanahan@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Huang, Kai" <kai.huang@...el.com>,
        "Zhang, Cathy" <cathy.zhang@...el.com>,
        "Xing, Cedric" <cedric.xing@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4 00/31] x86/sgx and selftests/sgx: Support SGX2

Hi Vijay,

On 4/25/2022 1:17 PM, Dhanraj, Vijay wrote:
>> On Thu, Apr 21, 2022 at 08:29:31PM -0700, Reinette Chatre wrote:
>>> On 4/21/2022 4:46 PM, Dhanraj, Vijay wrote:
>>>> I evaluated V4 patch changes with Gramine and ran into an issue when
>> trying to set EPC page permission to PROT_NONE. It looks like with V3 patch
>> series a change was introduced which requires kernel to have at least R
>> permission when calling RESTRICT IOCTL. This change was done under the
>> assumption that EPCM requires at least R permission for EMODPE/EACCEPT
>> to succeed. But when testing with V2 version, EACCEPT worked fine with
>> page permission set to PROT_NONE.
>>>>
>>>> Thanks to @Shanahan, Mark for confirming that EPCM does not need to
>> have R value to allow EACCEPT or EMODPE. Given this, can we please revert
>> this change?
>>>>
>>>
>>> Thank you very much for pointing this out. I can revert the change to
>>> what was done in V2 where the only check is to ensure that W requires R.
>>> This is a requirement of EMODPR. Could you please check if this
>>> snippet results in things working for you again?
>>>
>>> ---8<---
>>> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c
>>> b/arch/x86/kernel/cpu/sgx/ioctl.c index 83674d054c13..7c7c8a61196e
>>> 100644
>>> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
>>> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
>>> @@ -855,12 +855,8 @@ static long
>> sgx_ioc_enclave_restrict_permissions(struct sgx_encl *encl,
>>>  	if (params.permissions & ~SGX_SECINFO_PERMISSION_MASK)
>>>  		return -EINVAL;
>>>
>>> -	/*
>>> -	 * Read access is required for the enclave to be able to use the page.
>>> -	 * SGX instructions like ENCLU[EMODPE] and ENCLU[EACCEPT]
>> require
>>> -	 * read access.
>>> -	 */
>>> -	if (!(params.permissions & SGX_SECINFO_R))
>>> +	if ((params.permissions & SGX_SECINFO_W) &&
>>> +	    !(params.permissions & SGX_SECINFO_R))
>>>  		return -EINVAL;
>>>
>>>  	if (params.result || params.count)
>>
>> Just adding that it's fine for me to revert this.
> 
> Thanks, I verified your patch and now I am able to set EPCM page permission with PROT_NONE.
> 
> I also verified the following SGX2 interfaces,
> SGX_IOC_ENCLAVE_MODIFY_TYPES
> SGX_IOC_ENCLAVE_REMOVE_PAGES
> SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS
> 
> And also tested dynamically adding pages to enclave using #PF based approach and this works as expected.
> 
> Please feel free to add my Tested-by for the below patches which test the above IOCTLs
> 
> [PATCH V4 16/31] x86/sgx: Support adding of pages to an initialized enclave
> [PATCH V4 15/31] x86/sgx: Support restricting of enclave page permissions
> [PATCH V4 18/31] x86/sgx: Support modifying SGX page type
> [PATCH V4 19/31] x86/sgx: Support complete page removal
> 

Thank you very much for all the testing. I will include the above snippet into
V5 of "x86/sgx: Support restricting of enclave page permissions" and add your
Tested-by tag to the four patches you listed.

Reinette