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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 390CAC433DF for ; Fri, 29 May 2020 12:00:19 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0D5FB20776 for ; Fri, 29 May 2020 12:00:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0D5FB20776 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jedg6-0006pe-AY; Fri, 29 May 2020 11:59:58 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jedg5-0006pZ-Dp for xen-devel@lists.xenproject.org; Fri, 29 May 2020 11:59:57 +0000 X-Inumbo-ID: e9962128-a1a3-11ea-81bc-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id e9962128-a1a3-11ea-81bc-bc764e2007e4; Fri, 29 May 2020 11:59:56 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 2868EABBD; Fri, 29 May 2020 11:59:55 +0000 (UTC) Subject: Re: [PATCH v2 03/14] x86/shstk: Introduce Supervisor Shadow Stack support To: Andrew Cooper References: <20200527191847.17207-1-andrew.cooper3@citrix.com> <20200527191847.17207-4-andrew.cooper3@citrix.com> <4f535d4c-b3b3-fe5b-8b57-af736dc0a360@suse.com> From: Jan Beulich Message-ID: Date: Fri, 29 May 2020 13:59:55 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Anthony Perard , Xen-devel , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 28.05.2020 20:10, Andrew Cooper wrote: > On 28/05/2020 11:25, Jan Beulich wrote: >> On 27.05.2020 21:18, Andrew Cooper wrote: >>> --- a/xen/arch/x86/Kconfig >>> +++ b/xen/arch/x86/Kconfig >>> @@ -34,6 +34,10 @@ config ARCH_DEFCONFIG >>> config INDIRECT_THUNK >>> def_bool $(cc-option,-mindirect-branch-register) >>> >>> +config HAS_AS_CET >>> + # binutils >= 2.29 and LLVM >= 7 >>> + def_bool $(as-instr,wrssq %rax$(comma)0;setssbsy;endbr64) >> So you put me in a really awkward position: I'd really like to see >> this series go in for 4.14, yet I've previously indicated I want the >> underlying concept to first be agreed upon, before any uses get >> introduced. > > There are already users.  One of them is even in context. Hmm, indeed. I clearly didn't notice this aspect when reviewing Anthony's series. > I don't see that there is anything open for dispute in the first place.  > Being able to do exactly this was a one key driving factor to a newer > Kconfig, because it is superior mechanism to the ad-hoc mess we had > previously (not to mention, a vast detriment to build time). This "key driving factor" was presumably from your perspective. Could you point me to a discussion (and resulting decision) that this is an explicit goal of that work? I don't recall any, and hence I also don't recall having been given a chance in influence the direction, decision, and overall outcome. In the interest of getting this series in for 4.14, and on the assumption that you're willing to have a discussion on the direction wrt storing tool chain capabilities in .config before any further uses get added (and with the potential need to undo the ones we have / gain here) Reviewed-by: Jan Beulich The comment at the very end may point at an issue that wants sorting, the others below are merely replies to some of the points you've made. >> A fundamental problem with this, at least as long as (a) more of >> Anthony's series hasn't been committed and (b) we re-build Xen upon >> installing (as root), even if it was fully built (as non-root) and >> is ready without any re-building. > > How is any any of this relevant to Anthony's recent changes? Command line options not getting written to .*.cmd and read back and compare upon rebuild is the issue here. Albeit thinking about it again for anything that's stored in .config that's for now compensated for by a change to .config triggering a global rebuild. The specific issue I had run into was with XEN_BUILD_EFI changing without xen.lds getting re-generated. > You've always been asking for trouble if your `make` before `make > install` has as different toolchain, even in regular autotools/userspace > software.  The newer Kconfig logic might make this trouble far more > obvious, but doesn't introduce the problem. I disagree. There should be no dependency on the tool chain at all at install time, with a fully built tree. It ought to be fine to not even have a tool chain accessible to root, even less so the precise one that was used for building the tree. >>> --- a/xen/scripts/Kconfig.include >>> +++ b/xen/scripts/Kconfig.include >>> @@ -31,6 +31,10 @@ cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) $(1) -E -x c /dev/null -o /de >>> # Return y if the linker supports , n otherwise >>> ld-option = $(success,$(LD) -v $(1)) >>> >>> +# $(as-instr,) >>> +# Return y if the assembler supports , n otherwise >>> +as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler -o /dev/null -) >> Is this actually checking the right thing in the clang case? > > Appears to work correctly for me.  (Again, its either fine, or need > bugfixing anyway for 4.14, and raising with Linux as this is unmodified > upstream code like the rest of Kconfig.include). This answer made me try it out: On a system with clang 5 and binutils 2.32 "incsspd %eax" translates fine with -no-integrated-as but doesn't without. The previously mentioned odd use of CLANG_FLAGS, perhaps together with the disconnect from where we establish whether to use -no-integrated-as in the first place (arch.mk; I have no idea whether the CFLAGS determined would be usable by the kconfig invocation, nor how to solve the chicken-and-egg problem there if this is meant to work that way), may be the reason for this. Cc-ing Anthony once again ... As an aside - this being taken from Linux doesn't mean it's suitable for our use. For example, Linux'es way to use (or not) -no-integrated-as is entirely different from ours (via LLVM_IAS setting, used in the top level Makefile). I don't think I can see whether the check above, for the case at hand, would work correctly there, both with and without that variable set. Jan