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=-13.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 2F515C388F9 for ; Tue, 27 Oct 2020 15:12:24 +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 C173521D24 for ; Tue, 27 Oct 2020 15:12:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="dF8gVvsP"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="KnT5lraB" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C173521D24 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:MIME-Version:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-Id:Date:Subject:To:From:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Owner; bh=17dUAccDjWAM8awJhIx/aifSEjKh+7GFwD9zU84c+Ac=; b=dF8gVvsPbOhVGR4xOf//Wqs7/9 Z90o1796iI4zEYxzGSpp/wkxnKjHspWbVRQ2Jlacl2k+QEDx5GWbGB43avQzerOOsYn2Grmod1QUR vR2E1R4vdP8MDrkwvgKZUVpBhmbPwyzDduepesC+a5e8uZV50jrqyWr9+Ta4T3AjZGaL/bVV/q7TA eybTSU5+cZgKAkRU3wzwXur5YlHMnSFHUXLkhb4fZj6U/U48g2m+sSzciLEvL3OcWkdmm3GG5K31s luMtoHRDM+TNTStKOOdx4N7V4GcqcuZiwTVO+dVA5YJAoqFPov5X/CvaXb2KtiGBJQ+aMByQA4KpG Uk+IOswQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXQdc-0007Nk-70; Tue, 27 Oct 2020 15:11:52 +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 1kXQda-0007Mx-1F for linux-arm-kernel@lists.infradead.org; Tue, 27 Oct 2020 15:11:50 +0000 Received: from e123331-lin.nice.arm.com (lfbn-nic-1-188-42.w2-15.abo.wanadoo.fr [2.15.37.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B6EF820657; Tue, 27 Oct 2020 15:11:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603811509; bh=MEOHJpFg/hSBwnyU+/C/N9+Qa7RXtkpK49digCQfxBc=; h=From:To:Cc:Subject:Date:From; b=KnT5lraBfZ/7vx1hN0P7obGVygBSAmfYDK5mhWAeewS2ufv945b4XfWIPctftNSu2 6uV1JiXXLV7UI09v6GGxXzmfoI3hQKzpePSNzgHbsdJQDf3txT0lub1uHSc+Qo5OQJ lMeyoA/vUucITAcnBqlmd1TsxQJZ0VFWzZINtLi8= From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Subject: [PATCH] module: use hidden visibility for weak symbol references Date: Tue, 27 Oct 2020 16:11:32 +0100 Message-Id: <20201027151132.14066-1-ardb@kernel.org> X-Mailer: git-send-email 2.17.1 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201027_111150_200724_C8730BDA X-CRM114-Status: GOOD ( 18.67 ) 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 , Geert Uytterhoeven , Jessica Yu , will@kernel.org, Ard Biesheuvel , linux-arm-kernel@lists.infradead.org MIME-Version: 1.0 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 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(-) diff --git a/include/linux/module.h b/include/linux/module.h index 7ccdf87f376f..6264617bab4d 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -740,7 +740,7 @@ static inline bool within_module(unsigned long addr, const struct module *mod) } /* Get/put a kernel symbol (calls should be symmetric) */ -#define symbol_get(x) ({ extern typeof(x) x __attribute__((weak)); &(x); }) +#define symbol_get(x) ({ extern typeof(x) x __attribute__((weak,visibility("hidden"))); &(x); }) #define symbol_put(x) do { } while (0) #define symbol_put_addr(x) do { } while (0) -- 2.17.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel