From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7C57A8060D; Tue, 7 May 2024 22:58:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715122705; cv=none; b=Y7rLTIBI/NbfHbZD47qnHWlXMmQKEwReF+Ueu63tDnmH5esQGRbp5YAX2fs6dCt9gU2MJQ8KHKWK4a/p4Y8epUJjNPvYKlJDNRCBwpfOICoXouBIU3Z2SVMJdfQQN0V4JOxxtIdXszlhODgIiSvVClmBAa4b5L3Qhgw0xmNvmNg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715122705; c=relaxed/simple; bh=GV9fGJP89g5AslJ5zfrMFPFR094Dgndsw4GvTjbyES4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=REtoUVZ5/dX89jUC6DoyJ0ds1hboxIpAvoJe0cc+JAX2zfeGyHniPNR+zJZDUzZj8K3/x6rXSUSt1zrGaCliSvvsStgzGTUoDy0BqdiGrtnBCzGGbL9YP8ONWNsNsFj41viV7YurwLU8QwwDqUDxOapoEC614t3r+RuJVdFRFL0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UG5Yg7fN; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UG5Yg7fN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 547ABC3277B; Tue, 7 May 2024 22:58:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1715122705; bh=GV9fGJP89g5AslJ5zfrMFPFR094Dgndsw4GvTjbyES4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UG5Yg7fNvlo/bcL5RLmMY5mQJe/HsD6ZyhYpBMO2UTPxERqUgXONX32ZnR2u1mZ8T nQg163OOMRaGHHSGSP/CKCaCYaZQ0sLMug21AZd6Mxu/Ara24NGoCBxmTDfZXcd0gK HRu2SF4LGQvnEKOQ/LvAJ9zwKztRp+tgaNDr0XNQ3iRM7KdyoWy4Fdl0KSoFfvsiBH ZASZk7GPvMjSYcb/BiPNgufAXq01scQqeT81Xck5HgFwdSKy/yWVBLng4RplT+MZen AeOUNaf+idpvz4GCpKMhrZDsxls9KN/+XJTlWCE9fcMIUorGhxsuOpMP2dxtjlmW6Q kFfZ5G0373MkQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Sean Christopherson , Borislav Petkov , Sasha Levin , corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, peterz@infradead.org, paulmck@kernel.org, jpoimboe@kernel.org, tj@kernel.org, xiongwei.song@windriver.com, linux-doc@vger.kernel.org Subject: [PATCH AUTOSEL 6.8 17/23] cpu: Ignore "mitigations" kernel parameter if CPU_MITIGATIONS=n Date: Tue, 7 May 2024 18:56:43 -0400 Message-ID: <20240507225725.390306-17-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240507225725.390306-1-sashal@kernel.org> References: <20240507225725.390306-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.8.9 Content-Transfer-Encoding: 8bit From: Sean Christopherson [ Upstream commit ce0abef6a1d540acef85068e0e82bdf1fbeeb0e9 ] Explicitly disallow enabling mitigations at runtime for kernels that were built with CONFIG_CPU_MITIGATIONS=n, as some architectures may omit code entirely if mitigations are disabled at compile time. E.g. on x86, a large pile of Kconfigs are buried behind CPU_MITIGATIONS, and trying to provide sane behavior for retroactively enabling mitigations is extremely difficult, bordering on impossible. E.g. page table isolation and call depth tracking require build-time support, BHI mitigations will still be off without additional kernel parameters, etc. [ bp: Touchups. ] Signed-off-by: Sean Christopherson Signed-off-by: Borislav Petkov (AMD) Acked-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20240420000556.2645001-3-seanjc@google.com Signed-off-by: Sasha Levin --- Documentation/admin-guide/kernel-parameters.txt | 3 +++ arch/x86/Kconfig | 8 ++++++-- include/linux/cpu.h | 11 +++++++++++ kernel/cpu.c | 14 ++++++++++---- 4 files changed, 30 insertions(+), 6 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 31fdaf4fe9dd8..9bfc972af2403 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3399,6 +3399,9 @@ arch-independent options, each of which is an aggregation of existing arch-specific options. + Note, "mitigations" is supported if and only if the + kernel was built with CPU_MITIGATIONS=y. + off Disable all optional CPU mitigations. This improves system performance, but it may also diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 6f49999a6b838..bfccf1213871b 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2474,9 +2474,13 @@ menuconfig CPU_MITIGATIONS help Say Y here to enable options which enable mitigations for hardware vulnerabilities (usually related to speculative execution). + Mitigations can be disabled or restricted to SMT systems at runtime + via the "mitigations" kernel parameter. - If you say N, all mitigations will be disabled. You really - should know what you are doing to say so. + If you say N, all mitigations will be disabled. This CANNOT be + overridden at runtime. + + Say 'Y', unless you really know what you are doing. if CPU_MITIGATIONS diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 8654714421a0d..75f0344bd3b94 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -219,7 +219,18 @@ void cpuhp_report_idle_dead(void); static inline void cpuhp_report_idle_dead(void) { } #endif /* #ifdef CONFIG_HOTPLUG_CPU */ +#ifdef CONFIG_CPU_MITIGATIONS extern bool cpu_mitigations_off(void); extern bool cpu_mitigations_auto_nosmt(void); +#else +static inline bool cpu_mitigations_off(void) +{ + return true; +} +static inline bool cpu_mitigations_auto_nosmt(void) +{ + return false; +} +#endif #endif /* _LINUX_CPU_H_ */ diff --git a/kernel/cpu.c b/kernel/cpu.c index f8a0406ce8ba5..bac70ea54e349 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -3196,6 +3196,7 @@ void __init boot_cpu_hotplug_init(void) this_cpu_write(cpuhp_state.target, CPUHP_ONLINE); } +#ifdef CONFIG_CPU_MITIGATIONS /* * These are used for a global "mitigations=" cmdline option for toggling * optional CPU mitigations. @@ -3206,9 +3207,7 @@ enum cpu_mitigations { CPU_MITIGATIONS_AUTO_NOSMT, }; -static enum cpu_mitigations cpu_mitigations __ro_after_init = - IS_ENABLED(CONFIG_CPU_MITIGATIONS) ? CPU_MITIGATIONS_AUTO : - CPU_MITIGATIONS_OFF; +static enum cpu_mitigations cpu_mitigations __ro_after_init = CPU_MITIGATIONS_AUTO; static int __init mitigations_parse_cmdline(char *arg) { @@ -3224,7 +3223,6 @@ static int __init mitigations_parse_cmdline(char *arg) return 0; } -early_param("mitigations", mitigations_parse_cmdline); /* mitigations=off */ bool cpu_mitigations_off(void) @@ -3239,3 +3237,11 @@ bool cpu_mitigations_auto_nosmt(void) return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT; } EXPORT_SYMBOL_GPL(cpu_mitigations_auto_nosmt); +#else +static int __init mitigations_parse_cmdline(char *arg) +{ + pr_crit("Kernel compiled without mitigations, ignoring 'mitigations'; system may still be vulnerable\n"); + return 0; +} +#endif +early_param("mitigations", mitigations_parse_cmdline); -- 2.43.0