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 F3F3E15FCE9; Mon, 27 May 2024 19:19:09 +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=1716837550; cv=none; b=p5f1MMj8P9nN6S7irCyIoGhHYA9fHZSSSi3A3yNfbq18SaOvMqwRV6eIucJq3AALms7F8iuMgsgybDc8XN/XX3jtmax+jvhzE0EutC7i36U5jb17cvZ2mPPyeKQzZy1u6bVKKuTQ+Qb2m2HAZ3SyzETNnJQeookMa4kgVD2loC8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716837550; c=relaxed/simple; bh=wbn1pwDX8bcl70xK/+QX0IzHaNlL1g/OgDJgoETMSYs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=D3S3IauWw14aEBRfhANFEdXX7GT8KBY8MKo/hwe9x0CK499vBBJ7sYmtxgtlLTJQMhCBQMtbqc+n6N+/Ho7cqBshVo91asTMZFFiRbsfT02v9+tyTKyosbHISxZkzIMwYLyM/ZNw/Rszb2IYoIfKU3+GIgZnM3+kswxCzXsTjA4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=iXb+X9xD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="iXb+X9xD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87890C2BBFC; Mon, 27 May 2024 19:19:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1716837549; bh=wbn1pwDX8bcl70xK/+QX0IzHaNlL1g/OgDJgoETMSYs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iXb+X9xDb0+F9oDZ1EIuNuQDNJirQ9wAiaVRAHCXbfHuIMiUITXq494vTA5nzlyIJ DT0qIjfjWwSLhVvDcYJSlImbROt4t0LGSvSraT/AH5DQ72pvO048bnJ4XUH4Lz72en HGAcnmP8JMFY52ijBWWPA+kWREXKlmjAtHxZu0y8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sean Christopherson , "Borislav Petkov (AMD)" , Sasha Levin Subject: [PATCH 6.8 055/493] cpu: Ignore "mitigations" kernel parameter if CPU_MITIGATIONS=n Date: Mon, 27 May 2024 20:50:57 +0200 Message-ID: <20240527185631.106292948@linuxfoundation.org> X-Mailer: git-send-email 2.45.1 In-Reply-To: <20240527185626.546110716@linuxfoundation.org> References: <20240527185626.546110716@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.8-stable review patch. If anyone has any objections, please let me know. ------------------ 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