Message-ID: <4f50b3b3-2cd5-30a4-5715-3350ef2174d9@kernel.org>
Date:   Fri, 3 Dec 2021 16:38:06 -0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.2.0
Subject: Re: [PATCH 05/25] x86/sgx: Introduce runtime protection bits
Content-Language: en-US
To:     Reinette Chatre <reinette.chatre@intel.com>,
        dave.hansen@linux.intel.com, jarkko@kernel.org, tglx@linutronix.de,
        bp@alien8.de, mingo@redhat.com, linux-sgx@vger.kernel.org,
        x86@kernel.org
Cc:     seanjc@google.com, kai.huang@intel.com, cathy.zhang@intel.com,
        cedric.xing@intel.com, haitao.huang@intel.com,
        mark.shanahan@intel.com, hpa@zytor.com,
        linux-kernel@vger.kernel.org
References: <cover.1638381245.git.reinette.chatre@intel.com>
 <2f6b04dd8949591ee6139072c72eb93da3dd07b0.1638381245.git.reinette.chatre@intel.com>
 <db9b7bc9-fdca-4dd2-2c3f-3b7354c165bb@kernel.org>
 <c0aab85a-f6a1-ed5c-5540-b03778ffe24a@intel.com>
From:   Andy Lutomirski <luto@kernel.org>
In-Reply-To: <c0aab85a-f6a1-ed5c-5540-b03778ffe24a@intel.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 12/3/21 14:12, Reinette Chatre wrote:
> Hi Andy,
> 
> On 12/3/2021 11:28 AM, Andy Lutomirski wrote:
>> On 12/1/21 11:23, Reinette Chatre wrote:
>>> Enclave creators declare their paging permission intent at the time
>>> the pages are added to the enclave. These paging permissions are
>>> vetted when pages are added to the enclave and stashed off
>>> (in sgx_encl_page->vm_max_prot_bits) for later comparison with
>>> enclave PTEs.
>>>
>>
>> I'm a bit confused here. ENCLU[EMODPE] allows the enclave to change 
>> the EPCM permission bits however it likes with no oversight from the 
>> kernel.   So we end up with a whole bunch of permission masks:
> 
> Before jumping to the permission masks I would like to step back and 
> just confirm the context. We need to consider the following three 
> permissions:
> 
> EPCM permissions: the enclave page permissions maintained in the SGX 
> hardware. The OS is constrained here in that it cannot query the current 
> EPCM permissions. Even so, the OS needs to ensure PTEs are installed 
> appropriately (we do not want a RW PTE for a read-only enclave page)

Why not?  What's wrong with an RW PTE for a read-only enclave page?

If you convince me that this is actually important, then I'll read all 
the stuff below.