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=-8.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 73E88C43331 for ; Wed, 1 Apr 2020 17:55:00 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 3F87B20719 for ; Wed, 1 Apr 2020 17:54:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="QQDgi0Ga" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3F87B20719 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-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=bombadil.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=yAhaU2iKHGnHJHDYbY8vuTbi24Fhn15Na4FULqvbwFA=; b=QQDgi0GaqDGf/l DgaFQmdL0jIio1pl004jmMeThT9PWsO3arGE8EPiykGOzaCFxkcnf+JioUl1t8DkOSEruHD4go2z+ d5VdOqvsaqiOry3P+dh433SC+8WM2TRrNsAvj221omip2uhczSxs3zpPO+le+4de7+lLvKQ8A9Oa0 wIbB880zSCDPYxzX0HUDcAy3EIThQFDVhkLlfz9vV+ycHZSuZpjdMmq1JoquJXrCbCarl+jeAX1hh bn8qkappnIB+h9mZk95GIOvCQqTj/PHh12OZx9BYkhB71pjJZlVz7UL5TuiTP6YposXuRYD0wYfxf GdfwVZYcahEqQrzFG9qw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jJhZr-0007i3-EV; Wed, 01 Apr 2020 17:54:59 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jJhZn-0007hS-Om for linux-arm-kernel@lists.infradead.org; Wed, 01 Apr 2020 17:54:57 +0000 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 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-Disposition: inline In-Reply-To: <20200331194459.54740-1-broonie@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-20200401_105455_891039_3400DFD2 X-CRM114-Status: GOOD ( 21.87 ) 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: Mark Rutland , Kees Cook , Szabolcs Nagy , "stable@vger.kernel.org" , Amit Kachhap , Will Deacon , "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+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel