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From:   Jethro Beekman <jethro@fortanix.com>
To:     Dave Hansen <dave.hansen@intel.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        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>
CC:     "H. Peter Anvin" <hpa@zytor.com>,
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        Haitao Huang <haitao.huang@linux.intel.com>,
        "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
        "Dr. Greg" <greg@enjellic.com>
Subject: Re: [RFC PATCH v2 4/4] x86/vdso: Add __vdso_sgx_enter_enclave() to
 wrap SGX enclave transitions
Thread-Topic: [RFC PATCH v2 4/4] x86/vdso: Add __vdso_sgx_enter_enclave() to
 wrap SGX enclave transitions
Thread-Index: AQHUjljGdIrv8QEhmk6icaec8mjmDaVznP6AgADio4A=
Date:   Sat, 8 Dec 2018 08:15:38 +0000
Message-ID: <f595c046-682c-0d4a-ce68-44d4634cedf2@fortanix.com>
References: <20181206221922.31012-1-sean.j.christopherson@intel.com>
 <20181206221922.31012-5-sean.j.christopherson@intel.com>
 <f2b7df05-20ef-ac16-fc99-258c39d84666@fortanix.com>
 <59c989a1-e699-9665-780f-6dd263f41ce4@intel.com>
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On 2018-12-08 00:14, Dave Hansen wrote:
> On 12/7/18 10:15 AM, Jethro Beekman wrote:
>> This is not sufficient to support the Fortanix SGX ABI calling
>> convention, which was designed to be mostly compatible with the SysV
>> 64-bit calling convention. The following registers need to be passed i=
n
>> to an enclave from userspace: RDI, RSI, RDX, R8, R9, R10. The followin=
g
>> registers need to be passed out from an enclave to userspace: RDI, RSI=
,
>> RDX, R8, R9.
>=20
> Are you asking nicely to change the new Linux ABI to be consistent with=

> your existing ABI?  Or, are you saying that the new ABI *must* be
> compatible with this previous out-of-tree implementation?

What's being discussed here is one of the alternatives for SGX fault=20
handling, meant to improve the current status quo of having to use a=20
signal handler.

I'm merely providing a data point that the currently proposed solution=20
is not sufficient to support current use of the (ring 3) ENCLU=20
instruction. You might find this useful in determining whether proposed=20
kernel features will actually be used by users, and in further=20
developing this solution or other solutions to the fault handling issue.

If going with the vDSO solution, I think something with semantics closer =

to the actual instruction would be preferred, like the following:

notrace __attribute__((naked)) long __vdso_sgx_enclu_with_aep()
{
	asm volatile(
		"	lea	2f(%%rip), %%rcx\n"
		"1:	enclu\n"
		"2:     ret\n"
		".pushsection .fixup, \"ax\" \n"
		"3:	jmp 2b\n"
		".popsection\n"
		_ASM_VDSO_EXTABLE_HANDLE(1b, 3b)
		:::
	);
}

--
Jethro Beekman | Fortanix


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