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=-8.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 6D6B4C4363A for ; Wed, 28 Oct 2020 10:03:15 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 CF2EA246A5 for ; Wed, 28 Oct 2020 10:03:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="F31Q/GAo"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="zSE1DqcX" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CF2EA246A5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=NXELVHCe+AgT2LEwDCVAG90ROIq1NXqOY3haT9EPAmo=; b=F31Q/GAoXrtz2dBugu4WNdrZF TPdAbpzY31YwABP6kTbo7gDQvp+GRQ7dCJKrBgDoujO0XPi5cm+tEYAdXKhIUoMdudbflTSOaj9mG lxPlRAn4O7sLV+2k1W4kWXUX6ikMYspY94jd5dzyIErBalz5Z0F+Aiu85b2jj+jwGoMnKfjSs3LLp nxJBqbqsWalXIGaVJFYNLWklGiV/MawOla+wUeewmfqaa4c5NfkeDBnGSCRHRNFElf3sg/DWms46K aElBApGRP2+2yAjf7VF9nXkKYzxLx6aCPNY/ebpW3OeTniWfQagF2Mpz0qnLWuBrHhe/G8JKuAzhW LmKWGa/Rg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXiGZ-0002Fj-GP; Wed, 28 Oct 2020 10:01:15 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXiGG-0002CC-7J for linux-arm-kernel@lists.infradead.org; Wed, 28 Oct 2020 10:00:57 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 10B48246A3; Wed, 28 Oct 2020 10:00:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603879254; bh=Zt06lJI/dyFmw+ygkxHH5YVanDHB4SbCK4oB2OLbzQ8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=zSE1DqcXeyFOXYe0GIro3PncnXe5qeo/vOgtS4PXRISXJH1OqtuoIMS359F505mMk gzBvRfj63gy2UcWFHugd3z8J+g+Q3ltJIvRWwUVKOF9L2wXDOCEThpkxDbZ7xvQuQN MZxdVjMtsjlnbrZXEXq21q8GefUyyUDnTG3Wpo+c= Date: Wed, 28 Oct 2020 10:00:49 +0000 From: Will Deacon To: Ard Biesheuvel Subject: Re: [PATCH] module: use hidden visibility for weak symbol references Message-ID: <20201028100049.GA27873@willie-the-truck> References: <20201027151132.14066-1-ardb@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201027151132.14066-1-ardb@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201028_060056_482728_3A3779E7 X-CRM114-Status: GOOD ( 25.06 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kees Cook , catalin.marinas@arm.com, Nick Desaulniers , linux-kernel@vger.kernel.org, Geert Uytterhoeven , Jessica Yu , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Ard, On Tue, Oct 27, 2020 at 04:11:32PM +0100, Ard Biesheuvel wrote: > Geert reports that commit be2881824ae9eb92 ("arm64/build: Assert for > unwanted sections") results in build errors on arm64 for configurations > that have CONFIG_MODULES disabled. > > The commit in question added ASSERT()s to the arm64 linker script to > ensure that linker generated sections such as .got, .plt etc are empty, > but as it turns out, there are corner cases where the linker does emit > content into those sections. More specifically, weak references to > function symbols (which can remain unsatisfied, and can therefore not > be emitted as relative references) will be emitted as GOT and PLT > entries when linking the kernel in PIE mode (which is the case when > CONFIG_RELOCATABLE is enabled, which is on by default). > > What happens is that code such as > > struct device *(*fn)(struct device *dev); > struct device *iommu_device; > > fn = symbol_get(mdev_get_iommu_device); > if (fn) { > iommu_device = fn(dev); > > essentially gets converted into the following when CONFIG_MODULES is off: > > struct device *iommu_device; > > if (&mdev_get_iommu_device) { > iommu_device = mdev_get_iommu_device(dev); > > where mdev_get_iommu_device is emitted as a weak symbol reference into > the object file. The first reference is decorated with an ordinary > ABS64 data relocation (which yields 0x0 if the reference remains > unsatisfied). However, the indirect call is turned into a direct call > covered by a R_AARCH64_CALL26 relocation, which is converted into a > call via a PLT entry taking the target address from the associated > GOT entry. > > Given that such GOT and PLT entries are unnecessary for fully linked > binaries such as the kernel, let's give these weak symbol references > hidden visibility, so that the linker knows that the weak reference > via R_AARCH64_CALL26 can simply remain unsatisfied. > > Cc: Jessica Yu > Cc: Kees Cook > Cc: Geert Uytterhoeven > Cc: Nick Desaulniers > Signed-off-by: Ard Biesheuvel > --- > include/linux/module.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Cheers. I gave this a spin, but I unfortunately still see the following linker warning with allnoconfig: aarch64-linux-gnu-ld: warning: orphan section `.igot.plt' from `arch/arm64/kernel/head.o' being placed in section `.igot.plt' which looks unrelated to symbol_get(), but maybe it's worth knocking these things on the head (no pun intended) at the same time? Cheers, Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel