From patchwork Mon Feb 3 10:28:02 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Brodsky X-Patchwork-Id: 13957300 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 247E0C02193 for ; Mon, 3 Feb 2025 11:45:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=vkmJBE2xe1rD7fvTP6vWNu0WpILKMHVEtvlvMXZaL4Q=; b=bELm1/8Z+dgV063QwAFATFaFPm wJCl5wK//TFPQMZFJdWgdk3WyWMP2QTjZKPktGFXR2BG5949z0No9/RE8eLV631FANOOAP28Of/0f 1NmnP34PHICveUHYIljibhwe7fYUYGrU0Vfmy9mcjgQXgFr/l9lw7pjfKm2AJIDMNq15TszsNUXMW a5VspOHFiqJIm8Pf4RScJBiHNCmyUxFahcoN9xHUvscL4gC10DETWjOYWUnxjf/q+o4RbufTB7xvM kFDRB0FhmGxk9wshJpZe04iFz9ly+PppNJHXs0wv5jXYR01FrXhGDjJqRXD13MZja21C/EOpQM6QX /ZDhdGjA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1teutg-0000000FGoz-2lKO; Mon, 03 Feb 2025 11:45:48 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tetgx-0000000F7PJ-06Oh for linux-arm-kernel@bombadil.infradead.org; Mon, 03 Feb 2025 10:28:35 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Content-Transfer-Encoding:MIME-Version :References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To: Content-Type:Content-ID:Content-Description; bh=vkmJBE2xe1rD7fvTP6vWNu0WpILKMHVEtvlvMXZaL4Q=; b=alxfeKXxJ7aSdmRuqBDuL2s3gs Kust79Ay2ovL48tin0cjA6JRnWwuvUUL6v+aM0+o9vH8KPjJVxjWwTOjnkbpVXs79zcx/kPqkUVCw AKEYR0laNn1iHQr8bVNYyMVcfVuzLkHZEQOSB7ar3GK6YBoVxN0B3+cNN8ZhzEmsV0NKqS6yrMXxz Nl9wcxGIHhSw9ZAyCIdpstNfRizSncvm1Y3Jb/DS99psMUwmks3iLPm54aYTKOUeoc3cB/J+DUbAg LW5jDXyVTaitBGf+Zad0Dej3xUsvo3sxiGlZaNZU8Ux55yF8LbrO+Tm7QmhumR2PBGWR8DM1EUkga AL/7qAKw==; Received: from foss.arm.com ([217.140.110.172]) by desiato.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tetgt-0000000G3pM-3zQh for linux-arm-kernel@lists.infradead.org; Mon, 03 Feb 2025 10:28:33 +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 AA49E1476; Mon, 3 Feb 2025 02:28:55 -0800 (PST) Received: from e123572-lin.arm.com (e123572-lin.cambridge.arm.com [10.1.194.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7B5A13F63F; Mon, 3 Feb 2025 02:28:27 -0800 (PST) From: Kevin Brodsky To: linux-hardening@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Kevin Brodsky , Andrew Morton , Mark Brown , Catalin Marinas , Dave Hansen , David Howells , "Eric W. Biederman" , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Andy Lutomirski , Marc Zyngier , Peter Zijlstra , Pierre Langlois , Quentin Perret , "Mike Rapoport (IBM)" , Ryan Roberts , Thomas Gleixner , Will Deacon , Matthew Wilcox , Qi Zheng , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org Subject: [RFC PATCH 1/8] arm64: kpkeys: Avoid unnecessary writes to POR_EL1 Date: Mon, 3 Feb 2025 10:28:02 +0000 Message-ID: <20250203102809.1223255-2-kevin.brodsky@arm.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20250203102809.1223255-1-kevin.brodsky@arm.com> References: <20250203102809.1223255-1-kevin.brodsky@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250203_102832_390265_748D37F4 X-CRM114-Status: GOOD ( 12.70 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Nested uses of kpkeys guards are about to be introduced, which means that kpkeys_set_level() may not actually need to change the value of POR_EL1. Since updating POR_EL1 requires an expensive ISB, let's skip the write if the value is unchanged, by returning KPKEYS_PKEY_REG_INVAL. This will cause the matching kpkeys_restore_pkey_reg() call to bail out without calling arch_kpkeys_restore_pkey_reg(). Signed-off-by: Kevin Brodsky --- arch/arm64/include/asm/kpkeys.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h index 4854e1f3babd..3f16584d495a 100644 --- a/arch/arm64/include/asm/kpkeys.h +++ b/arch/arm64/include/asm/kpkeys.h @@ -27,8 +27,12 @@ static inline u64 por_set_kpkeys_level(u64 por, int level) static inline int arch_kpkeys_set_level(int level) { u64 prev_por = read_sysreg_s(SYS_POR_EL1); + u64 new_por = por_set_kpkeys_level(prev_por, level); - write_sysreg_s(por_set_kpkeys_level(prev_por, level), SYS_POR_EL1); + if (new_por == prev_por) + return KPKEYS_PKEY_REG_INVAL; + + write_sysreg_s(new_por, SYS_POR_EL1); isb(); return prev_por;