Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v26 10/22] x86/sgx: Linux Enclave Driver
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        linux-sgx@vger.kernel.org, akpm@linux-foundation.org,
        dave.hansen@intel.com, nhorman@redhat.com, npmccallum@redhat.com,
        haitao.huang@intel.com, andriy.shevchenko@linux.intel.com,
        tglx@linutronix.de, kai.svahn@intel.com, bp@alien8.de,
        josh@joshtriplett.org, luto@kernel.org, kai.huang@intel.com,
        rientjes@google.com, cedric.xing@intel.com, puiterwijk@redhat.com,
        linux-security-module@vger.kernel.org,
        Suresh Siddha <suresh.b.siddha@intel.com>,
        Haitao Huang <haitao.huang@linux.intel.com>
References: <20200209212609.7928-1-jarkko.sakkinen@linux.intel.com>
 <20200209212609.7928-11-jarkko.sakkinen@linux.intel.com>
 <15074c16-4832-456d-dd12-af8548e46d6d@linux.microsoft.com>
 <20200220181345.GD3972@linux.intel.com>
 <7738b3cf-fb32-5306-5740-59974444e327@linux.microsoft.com>
 <20200220184842.GE3972@linux.intel.com>
 <20200220221607.GB26618@linux.intel.com>
From:   Jordan Hand <jorhand@linux.microsoft.com>
Message-ID: <2c077197-a8a7-feac-58ea-e901c92fb58b@linux.microsoft.com>
Date:   Thu, 20 Feb 2020 16:11:04 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.4.1
MIME-Version: 1.0
In-Reply-To: <20200220221607.GB26618@linux.intel.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2/20/20 2:16 PM, Jarkko Sakkinen wrote:
> On Thu, Feb 20, 2020 at 10:48:42AM -0800, Sean Christopherson wrote:
>> My biggest concern for allowing PROT_EXEC if RIE is that it would result
>> in #PF(SGX) (#GP on Skylake) due to an EPCM violation if the enclave
>> actually tried to execute from such a page.  This isn't a problem for the
>> kernel as the fault will be reported cleanly through the vDSO (or get
>> delivered as a SIGSEGV if the enclave isn't entered through the vDSO), but
>> it's a bit weird for userspace as userspace will see the #PF(SGX) and
>> likely assume the EPC was lost, e.g. silently restart the enclave instead
>> of logging an error that the enclave is broken.
> 
> I think right way to fix the current implementation is to -EACCES mmap()
> (and mprotect) when !!(current->personality & READ_IMPLIES_EXEC).
> 

I agree. It still means userspace code with an executable stack can't
mmap/mprotect enclave pages and request PROT_READ but the check you've
proposed would more consistently enforce this which is easier to
understand from userspace perspective.

-Jordan