linux-kernel - Re: [PATCH RFC] selftests/x86: Add a selftest for SGX

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Date:   Wed, 14 Nov 2018 08:09:42 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        linux-sgx@...r.kernel.org, dave.hansen@...el.com,
        nhorman@...hat.com, npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...el.com,
        andriy.shevchenko@...ux.intel.com, tglx@...utronix.de,
        kai.svahn@...el.com, Shuah Khan <shuah@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Andy Lutomirski <luto@...nel.org>,
        Dmitry Safonov <dima@...sta.com>,
        Florian Weimer <fweimer@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH RFC] selftests/x86: Add a selftest for SGX

On Tue, Nov 13, 2018 at 11:40:09PM +0200, Jarkko Sakkinen wrote:
> Add a selftest for SGX. It is a trivial test where a simple enclave
> copies one 64-bit word of memory between two memory locations given to
> the enclave as arguments.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> ---
> +SUBDIRS_64 := sgx
> +ASSERT(!DEFINED(.altinstructions), "ALTERNATIVES are not supported in the SGX LE")
> +ASSERT(!DEFINED(.altinstr_replacement), "ALTERNATIVES are not supported in the SGX LE")
> +ASSERT(!DEFINED(.discard.retpoline_safe), "RETPOLINE ALTERNATIVES are not supported in the SGX LE")
> +ASSERT(!DEFINED(.discard.nospec), "RETPOLINE ALTERNATIVES are not supported in the SGX LE")

Maybe this?

s/LE/Test Enclave

> diff --git a/tools/testing/selftests/x86/sgx/encl_bootstrap.S b/tools/testing/selftests/x86/sgx/encl_bootstrap.S
> new file mode 100644
> index 000000000000..62251c7d9927
> --- /dev/null
> +++ b/tools/testing/selftests/x86/sgx/encl_bootstrap.S
> @@ -0,0 +1,94 @@
> +/* SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) */
> +/*
> + * Copyright(c) 2016-18 Intel Corporation.
> + */
> +
> +	.macro ENCLU
> +	.byte 0x0f, 0x01, 0xd7
> +	.endm
> +
> +	.section ".tcs", "a"
> +	.balign	4096
> +
> +	.fill	1, 8, 0			# STATE (set by CPU)
> +	.fill	1, 8, 0			# FLAGS
> +	.long	encl_ssa		# OSSA

Any reason not to do .quad for OSSA and OENTRY?

> +	.fill	1, 4, 0
> +	.fill	1, 4, 0			# CSSA (set by CPU)
> +	.fill	1, 4, 1			# NSSA
> +	.long	encl_entry		# OENTRY
> +	.fill	1, 4, 0
> +	.fill	1, 8, 0			# AEP (set by EENTER and ERESUME)
> +	.fill	1, 8, 0			# OFSBASE
> +	.fill	1, 8, 0			# OGSBASE
> +	.fill	1, 4, 0xFFFFFFFF 	# FSLIMIT
> +	.fill	1, 4, 0xFFFFFFFF	# GSLIMIT
> +	.fill	503, 8, 0		# Reserved

I'd prefer to do 1-byte fill with a size of 4024 to match the SDM.

> +
> +	.text
> +
> +encl_entry:
> +	# %rbx contains the base address for TCS, which is also the first
> +	# address inside the enclave. By adding $le_stack_end to it, we get the
> +	# absolute address for the stack.
> +	lea	(encl_stack)(%rbx), %rax
> +	xchg	%rsp, %rax
> +	push	%rax
> +
> +	push	%rcx # push the address after EENTER
> +	push	%rbx # push the enclave base address
> +
> +	call	encl_body
> +
> +	pop	%rbx # pop the enclave base address
> +
> +	# Restore XSAVE registers to a synthetic state.
> +	mov     $0xFFFFFFFF, %rax
> +	mov     $0xFFFFFFFF, %rdx
> +	lea	(xsave_area)(%rbx), %rdi
> +	fxrstor	(%rdi)
> +
> +	# Clear GPRs
> +	xor     %rcx, %rcx
> +	xor     %rdx, %rdx
> +	xor     %rdi, %rdi
> +	xor     %rsi, %rsi
> +	xor     %r8, %r8
> +	xor     %r9, %r9
> +	xor     %r10, %r10
> +	xor     %r11, %r11
> +	xor     %r12, %r12
> +	xor     %r13, %r13
> +	xor     %r14, %r14
> +	xor     %r15, %r15
> +
> +	# Reset status flags
> +	add     %rdx, %rdx # OF = SF = AF = CF = 0; ZF = PF = 1
> +
> +	pop	%rbx # pop the address after EENTER

Probably worth expanding the comment to explain that ENCLU[EEXIT] takes the
target address via %rbx, i.e. we're "returning" from the EENTER "call".

> +
> +	# Restore the caller stack.
> +	pop	%rax
> +	mov	%rax, %rsp
> +
> +	# EEXIT
> +	mov	$4, %rax
> +	enclu
> +
> +	.section ".data", "aw"
> +
> +encl_ssa:
> +	.space 4096
> +
> +xsave_area:
> +	.fill	1, 4, 0x037F		# FCW
> +	.fill	5, 4, 0
> +	.fill	1, 4, 0x1F80		# MXCSR
> +	.fill	1, 4, 0xFFFF		# MXCSR_MASK
> +	.fill	123, 4, 0
> +	.fill	1, 4, 0x80000000	# XCOMP_BV[63] = 1, compaction mode
> +	.fill	12, 4, 0
> +
> +	.balign 4096
> +	.space 8192
> +encl_stack: