From patchwork Tue Sep 19 09:28:26 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 13391036 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 1F05ACD54AD for ; Tue, 19 Sep 2023 09:30:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=spEOXO4hyo0+/hyej+uC4/6NhUMYt8oA7TUi5U5yvQs=; b=Hm8tLkOsmYmkPK FOQRL195x3P+rDv6w9J013ph4eT/8eaoxyadECX6mZ4VGZFm+1OS+dJswRYrYEnfIhRRoJiKUrWwM NWyCKglNQFu8J56jetG57ButBLzse/IZLWnfKT9rn41QXeDKpekGyCszIxHQKRCBx3Sz+UyVNwc1p 5bS4cOQoBLVLC1HrzItyUNKZGhwGjKg2y95i6Oin6gNDmp2mUf8Hk3qvvB3L0gTnGuqDrSaWhlQrZ R/YX2ivPToLgheY5lMB43sYsi2fmD6IM5VY3XkHE+BkwxoHLZwtiNdfyyndwQ/zepNNVH2PBnXfWi qRXQjjrAXQy6vj9RGiYg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qiX3U-00HT63-0U; Tue, 19 Sep 2023 09:30:04 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qiX3C-00HSss-2p for linux-arm-kernel@lists.infradead.org; Tue, 19 Sep 2023 09:29:48 +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 99B28C15; Tue, 19 Sep 2023 02:30:23 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 24E353F59C; Tue, 19 Sep 2023 02:29:44 -0700 (PDT) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: ardb@kernel.org, bertrand.marquis@arm.com, boris.ostrovsky@oracle.com, broonie@kernel.org, catalin.marinas@arm.com, daniel.lezcano@linaro.org, james.morse@arm.com, jgross@suse.com, mark.rutland@arm.com, maz@kernel.org, oliver.upton@linux.dev, pcc@google.com, sstabellini@kernel.org, suzuki.poulose@arm.com, tglx@linutronix.de, vladimir.murzin@arm.com, will@kernel.org Subject: [PATCH 13/37] arm64: Avoid cpus_have_const_cap() for ARM64_HAS_{ADDRESS,GENERIC}_AUTH Date: Tue, 19 Sep 2023 10:28:26 +0100 Message-Id: <20230919092850.1940729-14-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20230919092850.1940729-1-mark.rutland@arm.com> References: <20230919092850.1940729-1-mark.rutland@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230919_022947_010404_1F929A1D X-CRM114-Status: GOOD ( 21.18 ) 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 In system_supports_address_auth() and system_supports_generic_auth() we use cpus_have_const_cap to check for ARM64_HAS_ADDRESS_AUTH and ARM64_HAS_GENERIC_AUTH respectively, but this is not necessary and alternative_has_cap_*() would bre preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. The ARM64_HAS_ADDRESS_AUTH cpucap is a boot cpu feature which is detected and patched early on the boot CPU before any pointer authentication keys are enabled via their respective SCTLR_ELx.EN* bits. Nothing which uses system_supports_address_auth() is called before the boot alternatives are patched. Thus it is safe for system_supports_address_auth() to use cpus_have_final_boot_cap() to check for ARM64_HAS_ADDRESS_AUTH. The ARM64_HAS_GENERIC_AUTH cpucap is a system feature which is detected on all CPUs, then finalized and patched under setup_system_capabilities(). We use system_supports_generic_auth() in a few places: * The pac_generic_keys_get() and pac_generic_keys_set() functions are only reachable from system calls once userspace is up and running. As cpucaps are finalzied long before userspace runs, these can safely use alternative_has_cap_*() or cpus_have_final_cap(). * The ptrauth_prctl_reset_keys() function is only reachable from system calls once userspace is up and running. As cpucaps are finalized long before userspace runs, this can safely use alternative_has_cap_*() or cpus_have_final_cap(). * The ptrauth_keys_install_user() function is used during context-switch. This is called prior to alternatives being applied, and so cannot use cpus_have_final_cap(), but as this only needs to switch the APGA key for userspace tasks, it's safe to use alternative_has_cap_*(). * The ptrauth_keys_init_user() function is used to initialize userspace keys, and is only reachable after system cpucaps have been finalized and patched. Thus this can safely use alternative_has_cap_*() or cpus_have_final_cap(). * The system_has_full_ptr_auth() helper function is only used by KVM code, which is only reachable after system cpucaps have been finalized and patched. Thus this can safely use alternative_has_cap_*() or cpus_have_final_cap(). This patch modifies system_supports_address_auth() to use cpus_have_final_boot_cap() to check ARM64_HAS_ADDRESS_AUTH, and modifies system_supports_generic_auth() to use alternative_has_cap_unlikely() to check ARM64_HAS_GENERIC_AUTH. In either case this will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. The use of cpus_have_final_boot_cap() will make it easier to spot if code is chaanged such that these run before the relevant cpucap is guaranteed to have been finalized. Signed-off-by: Mark Rutland Cc: Ard Biesheuvel Cc: Catalin Marinas Cc: Suzuki K Poulose Cc: Will Deacon --- arch/arm64/include/asm/cpufeature.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 9f4569fce2129..58f762df1d0d1 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -806,12 +806,12 @@ static __always_inline bool system_supports_cnp(void) static inline bool system_supports_address_auth(void) { - return cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH); + return cpus_have_final_boot_cap(ARM64_HAS_ADDRESS_AUTH); } static inline bool system_supports_generic_auth(void) { - return cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH); + return alternative_has_cap_unlikely(ARM64_HAS_GENERIC_AUTH); } static inline bool system_has_full_ptr_auth(void)