From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1517189168; cv=none; d=google.com; s=arc-20160816; b=puvKOt5p6vzLVioJPZgWCP5bObw5jAIQC/1nceVYNBUA1kTL8TuLEpdRTYGCWFx0Ox D883nSJT/bEkuXJGV1OJxjLDEqvQpCR7fKRHOD7+yRUB0v9dPy90WoLSd9MTy2djdmZj EoFJpYXZkGIOdCF6A6E4RZiUvYi1/d7SCJqi/NSfrkFgIWiRLBqwrvGfhFDXtpHPiGm4 +qOUp2MmYCi45xoqEh57B65ZTMIEoVM2z9BdnXfWHRgMt0fiJ3bKupSUkCICV/nNvIzw xPCMTG3geWUd2UjWGRCGrY0b/+9qtUhXbrVz7PDJqh9ST2HIaOZkWfbFQwLPjoRAWxgP n16Q== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject:sender :dkim-signature:arc-authentication-results; bh=cWB5OxBhTHqTRGPqLpOPkBM0+odljJSdaxoj3AaJAxw=; b=kYup4TtLyuSRGcoK2ODCETp6H5jZP1cmENBOEkP1MhE7GdhGAeFEMT4F9+DuAjsojB 4XB1CjwKNDl0cn/tOwuRwdWg4BVRZcqoKuwjW5OTu1Sntotwz6YlLjpmLyXcKGtTF1PV w75VMhaZclasOu72JjFlAI1r2MUmy9XbLFsmua+ZMZiC+5LpwTw7HFRb2UGAIMRuoeFh 1GNBDxyjR4f5W2/3poFNdlqNr/0p/ND91oGZxE8u8qRjFvp654JMArN7tticAyw/+ruO PTnDG5/WMEGOt2xayW53THGmlWKvXFwGygbinlW03nag6PklBah3AMNFZXTe1L/la5QZ bJuA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=RWDWJrsj; 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=RWDWJrsj; 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: AH8x226f4WT4HcMClXGMvwlwJRHvMbY/7K/QUWqttp2eUIMe4qiByRhzjkXIPGSUNEGnavNpBCOsVg== Sender: Guenter Roeck Subject: Re: [v8,02/12] objtool: Allow alternatives to be ignored To: Josh Poimboeuf Cc: David Woodhouse , Andi Kleen , Paul Turner , LKML , Linus Torvalds , Greg Kroah-Hartman , Tim Chen , Dave Hansen , tglx@linutronix.de, Kees Cook , Rik van Riel , Peter Zijlstra , Andy Lutomirski , Jiri Kosina , gnomes@lxorguk.ukuu.org.uk, x86@kernel.org, thomas.lendacky@amd.com References: <1515707194-20531-3-git-send-email-dwmw@amazon.co.uk> <20180118190931.GA27143@roeck-us.net> <20180118193315.zrrya7qo6kf7pmzp@treble> <20180118194112.GA28449@roeck-us.net> <1516649644.9521.61.camel@infradead.org> <20180122202522.GA29081@roeck-us.net> <20180128210642.xob2win53h2gztak@treble> From: Guenter Roeck Message-ID: <0a35672a-5bec-d4b2-732b-805b09d7b39b@roeck-us.net> Date: Sun, 28 Jan 2018 17:26:05 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <20180128210642.xob2win53h2gztak@treble> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1589334210253041473?= X-GMAIL-MSGID: =?utf-8?q?1590888150132834332?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 01/28/2018 01:06 PM, Josh Poimboeuf wrote: > On Mon, Jan 22, 2018 at 12:25:22PM -0800, Guenter Roeck wrote: >> Hi David, >> >> On Mon, Jan 22, 2018 at 07:34:04PM +0000, David Woodhouse wrote: >>> On Thu, 2018-01-18 at 11:41 -0800, Guenter Roeck wrote: >>>> >>>>> Not sure, does your gcc have retpolines?  Give me your .o file and I can >>>>> diagnose it. >>>>> >>>> Yes, it does, only it is the gcc from the Google toolchain which may >>>> generate different code than the upstream version. >>>> >>>> I attached an affected object file. Please let me know if there is anything else >>>> I can do to help. >>> Disassembly of section .text.__x86.indirect_thunk: >>> >>> 0000000000000000 <__x86.indirect_thunk>: >>>    0: e8 04 00 00 00        callq  9 <__x86.indirect_thunk+0x9> >>>    5: f3 90                 pause >>>    7: eb fc                 jmp    5 <__x86.indirect_thunk+0x5> >>>    9: 48 8d 64 24 08        lea    0x8(%rsp),%rsp >>>    e: c3                    retq >>> >>> That has the old-style CET-incompatible retpoline in a COMDAT section >>> in the .o file. What compiler options are being used for that? The >>> kernel should only use retpoline if GCC supports both of >>> -mindirect-branch=thunk-extern and -mindirect-branch-register, and this >>> compiler is doing *neither* of those. >> >> It uses "-mindirect-branch=thunk -mindirect-branch-loop=pause >> -fno-jump-tables", though I don't know if that even exists in >> upstream gcc (it is the gcc use for Chrome OS builds). I'll pass >> your feedback to our compiler team. >> >> Either case, I think it is less than optimal that objtool crashes >> with _any_ object code. > > I've got a pending fix for this, so that objtool doesn't seg fault, and > instead prints out a warning: > > quirks.o: warning: objtool: efi_delete_dummy_variable()+0x99: unsupported intra-function call > quirks.o: warning: objtool: If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE. > > The code is here, along with a few more fixes: > > https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=TODO-objtool-seg-fault > Excellent. I'll give it a try tomorrow. Thanks for looking into this! Guenter