linux-kernel - Re: [PATCH v26 10/22] x86/sgx: Linux Enclave Driver

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Message-ID: <20200220221607.GB26618@linux.intel.com>
Date:   Fri, 21 Feb 2020 00:16:07 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Jordan Hand <jorhand@...ux.microsoft.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, nhorman@...hat.com, npmccallum@...hat.com,
        haitao.huang@...el.com, andriy.shevchenko@...ux.intel.com,
        tglx@...utronix.de, kai.svahn@...el.com, bp@...en8.de,
        josh@...htriplett.org, luto@...nel.org, kai.huang@...el.com,
        rientjes@...gle.com, cedric.xing@...el.com, puiterwijk@...hat.com,
        linux-security-module@...r.kernel.org,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>
Subject: Re: [PATCH v26 10/22] x86/sgx: Linux Enclave Driver

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).

This way supporting RIE can be reconsidered later on without any
potential ABI bottlenecks.

/Jarkko