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;
Date:   Fri, 14 Dec 2018 07:38:30 -0800
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Jethro Beekman <jethro@fortanix.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "x86@kernel.org" <x86@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Josh Triplett <josh@joshtriplett.org>,
        Haitao Huang <haitao.huang@linux.intel.com>,
        "Dr . Greg Wettstein" <greg@enjellic.com>
Subject: Re: [RFC PATCH v4 5/5] x86/vdso: Add __vdso_sgx_enter_enclave() to
 wrap SGX enclave transitions
Message-ID: <20181214153830.GB22063@linux.intel.com>
References: <20181213213135.12913-1-sean.j.christopherson@intel.com>
 <20181213213135.12913-6-sean.j.christopherson@intel.com>
 <cda13cff-1a56-a40f-7d69-f0f1ab752f8e@fortanix.com>
 <20181214151204.GA22063@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20181214151204.GA22063@linux.intel.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Dec 14, 2018 at 07:12:04AM -0800, Sean Christopherson wrote:
> On Fri, Dec 14, 2018 at 09:55:49AM +0000, Jethro Beekman wrote:
> > On 2018-12-14 03:01, Sean Christopherson wrote:
> > >+2:	pop	%rbx
> > >+	pop	%r12
> > >+	pop	%r13
> > >+	pop	%r14
> > >+	pop	%r15
> > >+	pop	%rbp
> > >+	ret
> > 
> > x86-64 ABI requires that you call CLD here (enclave may set it).
> 
> Ugh.  Technically MXCSR and the x87 CW also need to be preserved.
> 
> What if rather than treating the enclave as hostile we require it to be
> compliant with the x86-64 ABI like any other function?  That would solve
> the EFLAGS.DF, MXCSR and x87 issues without adding unnecessary overhead.
> And we wouldn't have to save/restore R12-R15.  It'd mean we couldn't use
> the stack's red zone to hold @regs and @e, but that's poor form anyways.

Grr, except the processor crushes R12-R15, FCW and MXCSR on asynchronous
exits.  But not EFLAGS.DF, that's real helpful.