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02 Nov 2018 10:13:23 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,456,1534834800"; d="scan'208";a="246537096" Received: from ray.jf.intel.com (HELO [10.7.201.133]) ([10.7.201.133]) by orsmga004.jf.intel.com with ESMTP; 02 Nov 2018 10:13:23 -0700 Subject: Re: RFC: userspace exception fixups To: Sean Christopherson Cc: Andy Lutomirski , Linus Torvalds , Rich Felker , Jann Horn , Dave Hansen , Jethro Beekman , Jarkko Sakkinen , Florian Weimer , Linux API , X86 ML , linux-arch , LKML , Peter Zijlstra , nhorman@redhat.com, npmccallum@redhat.com, "Ayoun, Serge" , shay.katz-zamir@intel.com, linux-sgx@vger.kernel.org, Andy Shevchenko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Carlos O'Donell , adhemerval.zanella@linaro.org References: <20181101185225.GC5150@brightrain.aerifal.cx> <20181101193107.GE5150@brightrain.aerifal.cx> <20181102163034.GB7393@linux.intel.com> <7050972d-a874-dc08-3214-93e81181da60@intel.com> <20181102170627.GD7393@linux.intel.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181102170627.GD7393@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/2/18 10:06 AM, Sean Christopherson wrote: > On Fri, Nov 02, 2018 at 09:56:44AM -0700, Dave Hansen wrote: >> On 11/2/18 9:30 AM, Sean Christopherson wrote: >>> What if rather than having userspace register an address for fixup, the >>> kernel instead unconditionally does fixup on the ENCLU opcode? >> >> The problem is knowing what to do for the fixup. If we have a simple >> action to take that's universal, like backing up %RIP, or setting some >> other register state, it's not bad. > > Isn't the EENTER/RESUME behavior universal? Or am I missing something? Could someone write down all the ways we get in and out of the enclave? I think we always get in from userspace calling EENTER or ERESUME. We can't ever enter directly from the kernel, like via an IRET from what I understand. We get *out* from exceptions, hardware interrupts, or enclave-explicit EEXITs. Did I miss any? Remind me where the hardware lands the control flow in each of those exit cases.