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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 AD716C2D0F2 for ; Wed, 1 Apr 2020 17:54:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7FCF820719 for ; Wed, 1 Apr 2020 17:54:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732461AbgDARyx (ORCPT ); Wed, 1 Apr 2020 13:54:53 -0400 Received: from foss.arm.com ([217.140.110.172]:58090 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726974AbgDARyx (ORCPT ); Wed, 1 Apr 2020 13:54:53 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 35A061FB; Wed, 1 Apr 2020 10:54:52 -0700 (PDT) Received: from mbp (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 062EA3F52E; Wed, 1 Apr 2020 10:54:50 -0700 (PDT) Date: Wed, 1 Apr 2020 18:54:44 +0100 From: Catalin Marinas To: Mark Brown Cc: Will Deacon , Mark Rutland , Amit Kachhap , Kees Cook , "linux-arm-kernel@lists.infradead.org" , Szabolcs Nagy , "stable@vger.kernel.org" Subject: Re: [PATCH] arm64: Always force a branch protection mode when the compiler has one Message-ID: <20200401175444.GF9434@mbp> References: <20200331194459.54740-1-broonie@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200331194459.54740-1-broonie@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Tue, Mar 31, 2020 at 08:44:59PM +0100, Mark Brown wrote: > Compilers with branch protection support can be configured to enable it by > default, it is likely that distributions will do this as part of deploying > branch protection system wide. As well as the slight overhead from having > some extra NOPs for unused branch protection features this can cause more > serious problems when the kernel is providing pointer authentication to > userspace but not built for pointer authentication itself. With 5.7 you won't be able to configure user and kernel PAC support independently. So, I guess that's something only for prior kernel versions. > In that case our > switching of keys for userspace can affect the kernel unexpectedly, causing > pointer authentication instructions in the kernel to corrupt addresses. > > To ensure that we get consistent and reliable behaviour always explicitly > initialise the branch protection mode, ensuring that the kernel is built > the same way regardless of the compiler defaults. > > Fixes: 7503197562567 (arm64: add basic pointer authentication support) > Reported-by: Szabolcs Nagy > Signed-off-by: Mark Brown > Cc: stable@vger.kernel.org > --- > arch/arm64/Kconfig | 4 ++++ > arch/arm64/Makefile | 7 ++++++- > 2 files changed, 10 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index d3efdc095a17..1e46746e8392 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1537,6 +1537,10 @@ config ARM64_PTR_AUTH > This feature works with FUNCTION_GRAPH_TRACER option only if > DYNAMIC_FTRACE_WITH_REGS is enabled. > > +config CC_HAS_BRANCH_PROT_NONE > + # GCC 9 or later, clang 8 or later > + def_bool $(cc-option,-mbranch-protection=none) I don't think we need to bother with a Kconfig entry here. We did it for the other options since CONFIG_ARM64_PTR_AUTH has a dependency on them. > + > config CC_HAS_BRANCH_PROT_PAC_RET > # GCC 9 or later, clang 8 or later > def_bool $(cc-option,-mbranch-protection=pac-ret+leaf) > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index f15f92ba53e6..370fca6663c8 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -65,6 +65,10 @@ stack_protector_prepare: prepare0 > include/generated/asm-offsets.h)) > endif > > +# Ensure that if the compiler supports branch protection we default it > +# off, this will be overridden if we are using branch protection. > +branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_NONE) := -mbranch-protection=none And a $(call cc-option,-mbranch-protection=none) here. branch-prot-flags-y is only introduced in 5.7, so backporting may look slightly weirder. > + > ifeq ($(CONFIG_ARM64_PTR_AUTH),y) > branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all > branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf > @@ -73,9 +77,10 @@ branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pa > # we pass it only to the assembler. This option is utilized only in case of non > # integrated assemblers. > branch-prot-flags-$(CONFIG_AS_HAS_PAC) += -Wa,-march=armv8.3-a > -KBUILD_CFLAGS += $(branch-prot-flags-y) > endif > > +KBUILD_CFLAGS += $(branch-prot-flags-y) Or just use an else clause here with: KBUILD_CFLAGS += ($call cc-option,-mbranch-protection=none). On backports, we just drop else/endif since they don't exist. Not a strong preference really, just looking to have backports resemble upstream better. I can fix it up locally, whichever variant we go for (or even this one). -- Catalin