From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A4DB5ECE599 for ; Wed, 16 Oct 2019 23:06:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7FB30207FF for ; Wed, 16 Oct 2019 23:06:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387985AbfJPXG6 (ORCPT ); Wed, 16 Oct 2019 19:06:58 -0400 Received: from mga12.intel.com ([192.55.52.136]:5138 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728424AbfJPXG6 (ORCPT ); Wed, 16 Oct 2019 19:06:58 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Oct 2019 16:06:57 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.67,305,1566889200"; d="scan'208";a="397333938" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by fmsmga006.fm.intel.com with ESMTP; 16 Oct 2019 16:06:57 -0700 Date: Wed, 16 Oct 2019 16:06:57 -0700 From: Sean Christopherson To: "Xing, Cedric" Cc: Jarkko Sakkinen , linux-sgx@vger.kernel.org Subject: Re: [PATCH for_v23 4/5] x86/vdso: sgx: Reorder params to callback to improve readability Message-ID: <20191016230657.GC8711@linux.intel.com> References: <20191011004059.28581-1-sean.j.christopherson@intel.com> <20191011004059.28581-5-sean.j.christopherson@intel.com> <34e9c245-34d5-fbd3-6d50-deac4adc29f6@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <34e9c245-34d5-fbd3-6d50-deac4adc29f6@intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org On Wed, Oct 16, 2019 at 03:24:54PM -0700, Xing, Cedric wrote: > On 10/10/2019 5:40 PM, Sean Christopherson wrote: > >Swap @ret and @ursp in the callback prototype so that the output from > >the vDSO itself, @ret and @e, are grouped together. Having the first > >N parameters all share a type also makes the prototype easier to parse > >by (some) humans. And, passing @ursp via register saves one whole > >MOV instruction! > > > >Signed-off-by: Sean Christopherson > >--- > > arch/x86/entry/vdso/vsgx_enter_enclave.S | 16 +++++++--------- > > arch/x86/include/uapi/asm/sgx.h | 10 +++++----- > > 2 files changed, 12 insertions(+), 14 deletions(-) > > > >diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S > >index 3dd22780b7ef..94f613b53b13 100644 > >--- a/arch/x86/entry/vdso/vsgx_enter_enclave.S > >+++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S > >@@ -134,23 +134,21 @@ ENTRY(__vdso_sgx_enter_enclave) > > jmp .Lhandle_exit > > .Linvoke_userspace_handler: > >+ /* Pass the untrusted RSP (at exit) to the callback via %rcx. */ > >+ mov %rsp, %rcx > >+ > > /* > >- * Align stack per x86_64 ABI. Save the original %rsp in %rbx to be > >- * restored after the callback returns. Note, %rsp needs to be 16-byte > >- * aligned _after_ pushing the three parameters on the stack. > >+ * Align stack per x86_64 ABI. Note, %rsp needs to be 16-byte aligned > >+ * _after_ pushing the three parameters on the stack. > > */ > >- mov %rsp, %rbx > > Per x86_64 ABI, %rcx is _not_ preserved across function call. How are you > going to restore the stack after callback returns? Magic? I completely spaced on restoring RSP, as evidenced by the fact that I didn't even change the restoration code to use RCX. > > > and $-0x10, %rsp > > sub $0x8, %rsp > > Usually compilers would just use a 1-byte "push" instead of a 4-byte "sub" > instruction here. Ah! Took me a minute to understand 'N-byte' was referring to the opcode... I'll update to use a push. > > >- /* Push @e, u_rsp and @tcs as parameters to the callback. */ > >+ /* Push @e, the "return" value and @tcs as params to the callback. */ > > push 0x18(%rbp) > >- push %rbx > >+ push %rax > > push 0x10(%rbp) > >- /* Pass the "return" value to the callback via %rcx. */ > >- mov %eax, %ecx > >- > > /* Clear RFLAGS.DF per x86_64 ABI */ > > cld > >diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h > >index 255392f5054f..95f69f938b58 100644 > >--- a/arch/x86/include/uapi/asm/sgx.h > >+++ b/arch/x86/include/uapi/asm/sgx.h > >@@ -88,16 +88,16 @@ struct sgx_enclave_exception { > > * @rdi: RDI at the time of enclave exit > > * @rsi: RSI at the time of enclave exit > > * @rdx: RDX at the time of enclave exit > >- * @ret: 0 on success (EEXIT), -EFAULT on an exception > >+ * @ursp: RSP at the time of enclave exit (untrusted stack) > > * @r8: R8 at the time of enclave exit > > * @r9: R9 at the time of enclave exit > > * @tcs: Thread Control Structure used to enter enclave > >- * @ursp: RSP at the time of enclave exit > >+ * @ret: 0 on success (EEXIT), -EFAULT on an exception > > * @e: Pointer to struct sgx_enclave_exception (as provided by caller) > > */ > >-typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx, int ret, > >- long r8, long r9, void *tcs, > >- long ursp, > >+typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx, > >+ long ursp, long r8, long r9, > >+ void *tcs, int ret, > > struct sgx_enclave_exception *e); > > #endif /* _UAPI_ASM_X86_SGX_H */ > >