linux-kernel - Re: [PATCH V4 15/31] x86/sgx: Support restricting of enclave page permissions

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Date:   Thu, 14 Apr 2022 09:31:13 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, <dave.hansen@...ux.intel.com>,
        <tglx@...utronix.de>, <bp@...en8.de>, <luto@...nel.org>,
        <mingo@...hat.com>, <linux-sgx@...r.kernel.org>, <x86@...nel.org>,
        <shuah@...nel.org>, <linux-kselftest@...r.kernel.org>
CC:     <seanjc@...gle.com>, <kai.huang@...el.com>,
        <cathy.zhang@...el.com>, <cedric.xing@...el.com>,
        <haitao.huang@...el.com>, <mark.shanahan@...el.com>,
        <vijay.dhanraj@...el.com>, <hpa@...or.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4 15/31] x86/sgx: Support restricting of enclave page
 permissions

Hi Jarkko,

On 4/14/2022 4:19 AM, Jarkko Sakkinen wrote:
> On Thu, 2022-04-14 at 14:19 +0300, Jarkko Sakkinen wrote:
>> On Wed, 2022-04-13 at 14:10 -0700, Reinette Chatre wrote:
>>> In the initial (SGX1) version of SGX, pages in an enclave need to be
>>> created with permissions that support all usages of the pages, from the
>>> time the enclave is initialized until it is unloaded. For example,
>>> pages used by a JIT compiler or when code needs to otherwise be
>>> relocated need to always have RWX permissions.
>>>
>>> SGX2 includes a new function ENCLS[EMODPR] that is run from the kernel
>>> and can be used to restrict the EPCM permissions of regular enclave
>>> pages within an initialized enclave.
>>>
>>> Introduce ioctl() SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS to support
>>> restricting EPCM permissions. With this ioctl() the user specifies
>>> a page range and the EPCM permissions to be applied to all pages in
>>> the provided range. ENCLS[EMODPR] is run to restrict the EPCM
>>> permissions followed by the ENCLS[ETRACK] flow that will ensure
>>> no cached linear-to-physical address mappings to the changed
>>> pages remain.
>>>
>>> It is possible for the permission change request to fail on any
>>> page within the provided range, either with an error encountered
>>> by the kernel or by the SGX hardware while running
>>> ENCLS[EMODPR]. To support partial success the ioctl() returns an
>>> error code based on failures encountered by the kernel as well
>>> as two result output parameters: one for the number of pages
>>> that were successfully changed and one for the SGX return code.
>>>
>>> The page table entry permissions are not impacted by the EPCM
>>> permission changes. VMAs and PTEs will continue to allow the
>>> maximum vetted permissions determined at the time the pages
>>> are added to the enclave. The SGX error code in a page fault
>>> will indicate if it was an EPCM permission check that prevented
>>> an access attempt.
>>>
>>> No checking is done to ensure that the permissions are actually
>>> being restricted. This is because the enclave may have relaxed
>>> the EPCM permissions from within the enclave without the kernel
>>> knowing. An attempt to relax permissions using this call will
>>> be ignored by the hardware.
>>>
>>> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
>>
>> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> 
> Also for this:
> 
> Tested-by: Jarkko Sakkinen <jarkko@...nel.org>
> 

Thank you very much.

Reinette