From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1517246128; cv=none; d=google.com; s=arc-20160816; b=sJJcQgkMmMdJAJr7qhYz0+7bZIWKQwNrhui8fshqA69ItYjzRYUEp0lPkCrjNGE9Do 4V84a6nmdopWVxfYXvuO02901fMsgoFGuIufKFMalh7q7kRDoKkV3Q4YQGL2qSbyKB2d cpOTrvi0iZW9u0qNve4uOj6v+0YvY0DuPq9ci7XpG3JV4R2HdsqoOPqqqExtIrqXskY5 MH4AVMG37s5ABIR26hJ2LV48lhMaC3ABj7TC+YDBcmhg9glK8ipzCVtVJ8DuS/XoOl25 YbB1TzbmgA7/JBqURNJnNEteQQgSP/YraCgnSqlNNsEbQ1AOYWxDmanfJeK+AFDOJmcy +Wog== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-transfer-encoding :content-disposition:mime-version:references:message-id:subject:cc :to:from:date:sender:dkim-signature:arc-authentication-results; bh=Ok69rFURI7au9jJS5mtIbMjUwqv7rhftJ/LtUgUO0HE=; b=acFWQvEaa2xyn99hrwbfo0BG0QTns7LXG34OXthOfVXKtuNsti6ocS3GABUnElgJoU w7WzNSfa71a5bBXJOQGsMzRgMzrpNdu+bYIBozUXSTC3GVqdIi4w+OSzK6EbzzeJfvnO ZbM4ElN09xQnUTh4ddMQB3T6Ztbps8xW/Uk5YvgzE5kEYNqhDtgmlq025u3vIkEg80S9 2edm+LPMx5fLUz6ZAlTyffcIzYqQ0iQa49PcwUow4vYP3TMQRL4JKhBoqIvfyCNUK7Le MwjwX6fYI1TmM38MJjW2w7CnWYiWb+9zDTRbIwHNqQ74f6wt45y+VhlBsXqquy7Trnkb BiAg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=dfFai7T1; 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=dfFai7T1; 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: AH8x2272Pdy8WmNxZ5aGREmQag1pGRawaGxw0ycSBWZYXHRxIs8+qv4yFhDqcCcV6GUnXhouIEyzfA== Sender: Guenter Roeck Date: Mon, 29 Jan 2018 09:15:26 -0800 From: Guenter Roeck 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 Subject: Re: [v8,02/12] objtool: Allow alternatives to be ignored Message-ID: <20180129171526.GA17121@roeck-us.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180128210642.xob2win53h2gztak@treble> User-Agent: Mutt/1.5.24 (2015-08-30) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1589334210253041473?= X-GMAIL-MSGID: =?utf-8?q?1590947876672190036?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Sun, Jan 28, 2018 at 03:06:42PM -0600, 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 > 'objtool: Improve retpoline alternative handling' works for me. Thanks! Guenter