From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1517949140; cv=none; d=google.com; s=arc-20160816; b=E5rMSq6bfA1p9xE2LzS2WcZdSxf9eUj4EhRCVVXUvSXW0FH/Xh31BmBjdCyTXwEio6 e7whp7uQv4CwpKPVrFB/0lcmaprFl6ChxUI21AMgVdsWMLzAFB2ksiyqwdZQIC+qdu1f ni+FMhguMRdwgWRCNfsreYXues5OCLNEeQBnOOnK9N7e/abhftjSalNPrC4QwTsIyyZQ TjSK5N++0xwLcAcB1qOMJctl8jIAanVO8ZmMcWcwJqpBW6A5+bs1JTd6w4zRyzCqgt1x WmdeXGRZWQPqLaFXB1i/Rd8NOoeGuGQbsrJk/VFNELWxZ3S93KMmAa3++Iu+1IJlH9oj EUBA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:sender:dkim-signature :arc-authentication-results; bh=6YV63gH0ZqPoAQsDYWCs7HH5NDcIvRgWkKmHv5HsQdM=; b=Unmars9tO58pFEPP4tfl28+t4qFTGOL0dqq2tVr5uqifJeZN+XzV1e9s3GLGi7wO+t i+9uN9FmfDbGwuH40wVQpjUb4ZuwX/xoEg8nn6VVqsP72KMpMNy6Tu7j/moHXdMaPui4 4UyVTIDoasFt5qshDiULR783R+F/MelJDaX70Ci2vnkq1xDY5+okjI7RnhL+skGNFDoY u9WiUn2Mm9qY5/ou37WZXn/hXk/FZRpDazh6v7GHm70zPR/6zE1BDy2j2b2vtYA/zwNj VseaUxkC6etmY0Seirv2kqne0w+yj9pWHsjuduc3EcqM/t1mfs8rTmCqqhIay4o1V1lh /Hbg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=VfAh91MV; spf=pass (google.com: domain of groeck7@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=groeck7@gmail.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=VfAh91MV; spf=pass (google.com: domain of groeck7@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=groeck7@gmail.com X-Google-Smtp-Source: AH8x225Je2zPc4eMYXyMrCeSC6yBBDa0HfzDOJXiWODwby0/HQ6nGmUGAN1NBY7vGob+2kUJrw4uqg== Sender: Guenter Roeck Date: Tue, 6 Feb 2018 12:32:18 -0800 From: Guenter Roeck To: Thomas Gleixner Cc: x86@kernel.org, linux-kernel@vger.kernel.org, David Woodhouse , Ingo Molnar , gnomes@lxorguk.ukuu.org.uk, Rik van Riel , Andi Kleen , Josh Poimboeuf , thomas.lendacky@amd.com, Peter Zijlstra , Linus Torvalds , Jiri Kosina , Andy Lutomirski , Dave Hansen , Kees Cook , Tim Chen , Greg Kroah-Hartman , Paul Turner Subject: Re: [RFC] x86/retpoline: Add clang support for 64-bit builds Message-ID: <20180206203218.GA11026@roeck-us.net> References: <1517614240-31269-1-git-send-email-linux@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1517614240-31269-1-git-send-email-linux@roeck-us.net> User-Agent: Mutt/1.5.24 (2015-08-30) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1591333873946801262?= X-GMAIL-MSGID: =?utf-8?q?1591685038434769651?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Fri, Feb 02, 2018 at 03:30:40PM -0800, Guenter Roeck wrote: > clang has its own set of compiler options for retpoline support. > Also, the thunks required by C code have their own function names. > > For 64-bit builds, there is only a single thunk, which is easy > to support. Support for 32-bit builds is more complicated - in > addition to various register thunks, there is also a thunk > named __llvm_external_retpoline_push which is more challenging. > Play it safe and only support 64-bit clang builds for now. > Feedback, anyone ? I understand that there is no love for the ABI differences between clang and gcc, but that doesn't help me. Even if the patch is unacceptable as-is, I would like to have some feedback to get an idea if I am on the right track, and what I would have to change to at least move into the right direction. Thanks, Guenter > Link: https://github.com/llvm-mirror/clang/commit/0d816739a82da29748caf88570affb9715e18b69 > Cc: David Woodhouse > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: gnomes@lxorguk.ukuu.org.uk > Cc: Rik van Riel > Cc: Andi Kleen > Cc: Josh Poimboeuf > Cc: thomas.lendacky@amd.com > Cc: Peter Zijlstra > Cc: Linus Torvalds > Cc: Jiri Kosina > Cc: Andy Lutomirski > Cc: Dave Hansen > Cc: Kees Cook > Cc: Tim Chen > Cc: Greg Kroah-Hartman > Cc: Paul Turner > Signed-off-by: Guenter Roeck > --- > Sent as RFC because I am not sure if the 64-bit only solution > is acceptable. > > arch/x86/Makefile | 5 ++++- > arch/x86/lib/retpoline.S | 24 ++++++++++++++++++++---- > 2 files changed, 24 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index fad55160dcb9..536dd6775988 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -232,7 +232,10 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > > # Avoid indirect branches in kernel to deal with Spectre > ifdef CONFIG_RETPOLINE > - RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register) > + RETPOLINE_CFLAGS = $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register) > + ifeq ($(RETPOLINE_CFLAGS)$(CONFIG_X86_32),) > + RETPOLINE_CFLAGS = $(call cc-option,-mretpoline -mretpoline-external-thunk) > + endif > ifneq ($(RETPOLINE_CFLAGS),) > KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE > endif > diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S > index 480edc3a5e03..f77738b13481 100644 > --- a/arch/x86/lib/retpoline.S > +++ b/arch/x86/lib/retpoline.S > @@ -9,14 +9,22 @@ > #include > #include > > -.macro THUNK reg > +.macro _THUNK prefix, reg > .section .text.__x86.indirect_thunk > > -ENTRY(__x86_indirect_thunk_\reg) > +ENTRY(\prefix\reg) > CFI_STARTPROC > JMP_NOSPEC %\reg > CFI_ENDPROC > -ENDPROC(__x86_indirect_thunk_\reg) > +ENDPROC(\prefix\reg) > +.endm > + > +.macro THUNK reg > +_THUNK __x86_indirect_thunk_ \reg > +.endm > + > +.macro CLANG_THUNK reg > +_THUNK __llvm_external_retpoline_ \reg > .endm > > /* > @@ -27,8 +35,11 @@ ENDPROC(__x86_indirect_thunk_\reg) > * the simple and nasty way... > */ > #define __EXPORT_THUNK(sym) _ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym) > -#define EXPORT_THUNK(reg) __EXPORT_THUNK(__x86_indirect_thunk_ ## reg) > +#define _EXPORT_THUNK(thunk, reg) __EXPORT_THUNK(thunk ## reg) > +#define EXPORT_THUNK(reg) _EXPORT_THUNK(__x86_indirect_thunk_, reg) > #define GENERATE_THUNK(reg) THUNK reg ; EXPORT_THUNK(reg) > +#define EXPORT_CLANG_THUNK(reg) _EXPORT_THUNK(__llvm_external_retpoline_, reg) > +#define GENERATE_CLANG_THUNK(reg) CLANG_THUNK reg ; EXPORT_CLANG_THUNK(reg) > > GENERATE_THUNK(_ASM_AX) > GENERATE_THUNK(_ASM_BX) > @@ -46,6 +57,11 @@ GENERATE_THUNK(r12) > GENERATE_THUNK(r13) > GENERATE_THUNK(r14) > GENERATE_THUNK(r15) > + > +#ifdef __clang__ > +GENERATE_CLANG_THUNK(r11) > +#endif > + > #endif > > /* > -- > 2.7.4 >