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Date: Wed, 29 Apr 2020 08:30:04 -0700 From: Sean Christopherson <sean.j.christopherson@...el.com> To: "Dr. Greg" <greg@...ellic.com> Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>, torvalds@...ux-foundation.org, 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 Subject: Re: [PATCH v29 00/20] Intel SGX foundations On Sun, Apr 26, 2020 at 11:57:53AM -0500, Dr. Greg wrote: > In closing, it is important to note that the proposed SGX driver is > not available as a module. This effectively excludes any alternative > implementations of the driver without replacement of the kernel at > large. No it doesn't. The SGX subsytem won't allocate EPC pages unless userspace creates an enclave, i.e. preventing unprivileged userspace from accessing /dev/sgx/enclave will allow loading an alternative out-of-tree SGX module. Yes, SGX sanitizes the EPC on boot, but that's arguably a good thing for out-of-tree modules. And if you want to get crafty and squash in-kernel SGX altogether, boot with "clearcpuid=<SGX_LC>" and/or "clearcpuid=<SGX>" to disable in-kernel support entirely. SGX won't be correctly enumerated in /proc/cpuinfo relative to the existence of an out-of-tree module, but that seems like a very minor issue if you're running with a completely different SGX driver. > It also means that any platform, with SGX hardware support, > running a kernel with this driver, has the potential for the > security/privacy issues noted above. Unless I'm mistaken, /dev/sgx is root-only by default. There are far scarier mechanisms available to root for hosing the system. > If key based policy management is not allowed, then the driver needs > to be re-architected to have modular support so that alternative > implementations or the absence of any driver support are at least > tenable. As above, using an alternative implementation is teneble, albeit a bit kludgy.
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