From patchwork Mon Apr 15 09:48:17 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Bader X-Patchwork-Id: 1923660 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@legolas.ozlabs.org Authentication-Results: legolas.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=lists.ubuntu.com (client-ip=185.125.189.65; helo=lists.ubuntu.com; envelope-from=kernel-team-bounces@lists.ubuntu.com; receiver=patchwork.ozlabs.org) Received: from lists.ubuntu.com (lists.ubuntu.com [185.125.189.65]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by legolas.ozlabs.org (Postfix) with ESMTPS id 4VJ2Rv5Qbzz1yY4 for ; Mon, 15 Apr 2024 19:48:43 +1000 (AEST) Received: from localhost ([127.0.0.1] helo=lists.ubuntu.com) by lists.ubuntu.com with esmtp (Exim 4.86_2) (envelope-from ) id 1rwIx3-0004Or-Je; Mon, 15 Apr 2024 09:48:37 +0000 Received: from smtp-relay-canonical-1.internal ([10.131.114.174] helo=smtp-relay-canonical-1.canonical.com) by lists.ubuntu.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1rwIwt-000498-4c for kernel-team@lists.ubuntu.com; Mon, 15 Apr 2024 09:48:27 +0000 Received: from canonical.com (2.general.smb.uk.vpn [10.172.193.29]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by smtp-relay-canonical-1.canonical.com (Postfix) with ESMTPSA id 7E8AA3F10F for ; Mon, 15 Apr 2024 09:48:26 +0000 (UTC) From: Stefan Bader To: kernel-team@lists.ubuntu.com Subject: [SRU Mantic][PATCH 6/9] x86/bhi: Add BHI mitigation knob Date: Mon, 15 Apr 2024 11:48:17 +0200 Message-Id: <20240415094820.399980-7-stefan.bader@canonical.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240415094820.399980-1-stefan.bader@canonical.com> References: <20240415094820.399980-1-stefan.bader@canonical.com> MIME-Version: 1.0 X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.20 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: "kernel-team" From: Pawan Gupta commit ec9404e40e8f36421a2b66ecb76dc2209fe7f3ef upstream. Branch history clearing software sequences and hardware control BHI_DIS_S were defined to mitigate Branch History Injection (BHI). Add cmdline spectre_bhi={on|off|auto} to control BHI mitigation: auto - Deploy the hardware mitigation BHI_DIS_S, if available. on - Deploy the hardware mitigation BHI_DIS_S, if available, otherwise deploy the software sequence at syscall entry and VMexit. off - Turn off BHI mitigation. The default is auto mode which does not deploy the software sequence mitigation. This is because of the hardening done in the syscall dispatch path, which is the likely target of BHI. Signed-off-by: Pawan Gupta Signed-off-by: Daniel Sneddon Signed-off-by: Thomas Gleixner Reviewed-by: Alexandre Chartre Reviewed-by: Josh Poimboeuf Signed-off-by: Daniel Sneddon Signed-off-by: Greg Kroah-Hartman CVE-2024-2201 (backported from commit d414b401f9539858574a19af4ffc0fc0d53bfb8f linux-6.6.y) [smb: context in cpufeatures.h] Signed-off-by: Stefan Bader --- Documentation/admin-guide/hw-vuln/spectre.rst | 45 ++++++++-- .../admin-guide/kernel-parameters.txt | 11 +++ arch/x86/Kconfig | 25 ++++++ arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/kernel/cpu/bugs.c | 90 ++++++++++++++++++- 5 files changed, 165 insertions(+), 7 deletions(-) diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst index 32a8893e5617..62c7902c66fd 100644 --- a/Documentation/admin-guide/hw-vuln/spectre.rst +++ b/Documentation/admin-guide/hw-vuln/spectre.rst @@ -138,11 +138,10 @@ associated with the source address of the indirect branch. Specifically, the BHB might be shared across privilege levels even in the presence of Enhanced IBRS. -Currently the only known real-world BHB attack vector is via -unprivileged eBPF. Therefore, it's highly recommended to not enable -unprivileged eBPF, especially when eIBRS is used (without retpolines). -For a full mitigation against BHB attacks, it's recommended to use -retpolines (or eIBRS combined with retpolines). +Previously the only known real-world BHB attack vector was via unprivileged +eBPF. Further research has found attacks that don't require unprivileged eBPF. +For a full mitigation against BHB attacks it is recommended to set BHI_DIS_S or +use the BHB clearing sequence. Attack scenarios ---------------- @@ -430,6 +429,21 @@ The possible values in this file are: 'PBRSB-eIBRS: Not affected' CPU is not affected by PBRSB =========================== ======================================================= + - Branch History Injection (BHI) protection status: + +.. list-table:: + + * - BHI: Not affected + - System is not affected + * - BHI: Retpoline + - System is protected by retpoline + * - BHI: BHI_DIS_S + - System is protected by BHI_DIS_S + * - BHI: SW loop + - System is protected by software clearing sequence + * - BHI: Syscall hardening + - Syscalls are hardened against BHI + Full mitigation might require a microcode update from the CPU vendor. When the necessary microcode is not available, the kernel will report vulnerability. @@ -484,7 +498,11 @@ Spectre variant 2 Systems which support enhanced IBRS (eIBRS) enable IBRS protection once at boot, by setting the IBRS bit, and they're automatically protected against - Spectre v2 variant attacks. + some Spectre v2 variant attacks. The BHB can still influence the choice of + indirect branch predictor entry, and although branch predictor entries are + isolated between modes when eIBRS is enabled, the BHB itself is not isolated + between modes. Systems which support BHI_DIS_S will set it to protect against + BHI attacks. On Intel's enhanced IBRS systems, this includes cross-thread branch target injections on SMT systems (STIBP). In other words, Intel eIBRS enables @@ -638,6 +656,21 @@ kernel command line. spectre_v2=off. Spectre variant 1 mitigations cannot be disabled. + spectre_bhi= + + [X86] Control mitigation of Branch History Injection + (BHI) vulnerability. Syscalls are hardened against BHI + regardless of this setting. This setting affects the deployment + of the HW BHI control and the SW BHB clearing sequence. + + on + unconditionally enable. + off + unconditionally disable. + auto + enable if hardware mitigation + control(BHI_DIS_S) is available. + For spectre_v2_user see Documentation/admin-guide/kernel-parameters.txt Mitigation selection guide diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 90ddf08e8409..bc154e4d7923 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5838,6 +5838,17 @@ sonypi.*= [HW] Sony Programmable I/O Control Device driver See Documentation/admin-guide/laptops/sonypi.rst + spectre_bhi= [X86] Control mitigation of Branch History Injection + (BHI) vulnerability. Syscalls are hardened against BHI + reglardless of this setting. This setting affects the + deployment of the HW BHI control and the SW BHB + clearing sequence. + + on - unconditionally enable. + off - unconditionally disable. + auto - (default) enable only if hardware mitigation + control(BHI_DIS_S) is available. + spectre_v2= [X86] Control mitigation of Spectre variant 2 (indirect branch speculation) vulnerability. The default operation protects the kernel from diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 68ce4f786dcd..8252ca11cd48 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2629,6 +2629,31 @@ config GDS_FORCE_MITIGATION If in doubt, say N. +choice + prompt "Clear branch history" + depends on CPU_SUP_INTEL + default SPECTRE_BHI_AUTO + help + Enable BHI mitigations. BHI attacks are a form of Spectre V2 attacks + where the branch history buffer is poisoned to speculatively steer + indirect branches. + See + +config SPECTRE_BHI_ON + bool "on" + help + Equivalent to setting spectre_bhi=on command line parameter. +config SPECTRE_BHI_OFF + bool "off" + help + Equivalent to setting spectre_bhi=off command line parameter. +config SPECTRE_BHI_AUTO + bool "auto" + help + Equivalent to setting spectre_bhi=auto command line parameter. + +endchoice + endif config ARCH_HAS_ADD_PAGES diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 8edd53a7b0d6..2066649b4ad0 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -457,6 +457,7 @@ * Reuse free bits when adding new feature flags! */ #define X86_FEATURE_BHI_CTRL (21*32+ 2) /* "" BHI_DIS_S HW control available */ +#define X86_FEATURE_CLEAR_BHB_HW (21*32+ 3) /* "" BHI_DIS_S HW control enabled */ /* * BUG word(s) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 50ba287497e9..4ff0095f7546 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1541,6 +1541,74 @@ static void __init spectre_v2_determine_rsb_fill_type_at_vmexit(enum spectre_v2_ dump_stack(); } +/* + * Set BHI_DIS_S to prevent indirect branches in kernel to be influenced by + * branch history in userspace. Not needed if BHI_NO is set. + */ +static bool __init spec_ctrl_bhi_dis(void) +{ + if (!boot_cpu_has(X86_FEATURE_BHI_CTRL)) + return false; + + x86_spec_ctrl_base |= SPEC_CTRL_BHI_DIS_S; + update_spec_ctrl(x86_spec_ctrl_base); + setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_HW); + + return true; +} + +enum bhi_mitigations { + BHI_MITIGATION_OFF, + BHI_MITIGATION_ON, + BHI_MITIGATION_AUTO, +}; + +static enum bhi_mitigations bhi_mitigation __ro_after_init = + IS_ENABLED(CONFIG_SPECTRE_BHI_ON) ? BHI_MITIGATION_ON : + IS_ENABLED(CONFIG_SPECTRE_BHI_OFF) ? BHI_MITIGATION_OFF : + BHI_MITIGATION_AUTO; + +static int __init spectre_bhi_parse_cmdline(char *str) +{ + if (!str) + return -EINVAL; + + if (!strcmp(str, "off")) + bhi_mitigation = BHI_MITIGATION_OFF; + else if (!strcmp(str, "on")) + bhi_mitigation = BHI_MITIGATION_ON; + else if (!strcmp(str, "auto")) + bhi_mitigation = BHI_MITIGATION_AUTO; + else + pr_err("Ignoring unknown spectre_bhi option (%s)", str); + + return 0; +} +early_param("spectre_bhi", spectre_bhi_parse_cmdline); + +static void __init bhi_select_mitigation(void) +{ + if (bhi_mitigation == BHI_MITIGATION_OFF) + return; + + /* Retpoline mitigates against BHI unless the CPU has RRSBA behavior */ + if (cpu_feature_enabled(X86_FEATURE_RETPOLINE) && + !(x86_read_arch_cap_msr() & ARCH_CAP_RRSBA)) + return; + + if (spec_ctrl_bhi_dis()) + return; + + if (!IS_ENABLED(CONFIG_X86_64)) + return; + + if (bhi_mitigation == BHI_MITIGATION_AUTO) + return; + + setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP); + pr_info("Spectre BHI mitigation: SW BHB clearing on syscall\n"); +} + static void __init spectre_v2_select_mitigation(void) { enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline(); @@ -1652,6 +1720,9 @@ static void __init spectre_v2_select_mitigation(void) mode == SPECTRE_V2_RETPOLINE) spec_ctrl_disable_kernel_rrsba(); + if (boot_cpu_has(X86_BUG_BHI)) + bhi_select_mitigation(); + spectre_v2_enabled = mode; pr_info("%s\n", spectre_v2_strings[mode]); @@ -2664,6 +2735,21 @@ static char *pbrsb_eibrs_state(void) } } +static const char * const spectre_bhi_state(void) +{ + if (!boot_cpu_has_bug(X86_BUG_BHI)) + return "; BHI: Not affected"; + else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_HW)) + return "; BHI: BHI_DIS_S"; + else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP)) + return "; BHI: SW loop"; + else if (boot_cpu_has(X86_FEATURE_RETPOLINE) && + !(x86_read_arch_cap_msr() & ARCH_CAP_RRSBA)) + return "; BHI: Retpoline"; + + return "; BHI: Vulnerable (Syscall hardening enabled)"; +} + static ssize_t spectre_v2_show_state(char *buf) { if (spectre_v2_enabled == SPECTRE_V2_LFENCE) @@ -2676,13 +2762,15 @@ static ssize_t spectre_v2_show_state(char *buf) spectre_v2_enabled == SPECTRE_V2_EIBRS_LFENCE) return sysfs_emit(buf, "Vulnerable: eIBRS+LFENCE with unprivileged eBPF and SMT\n"); - return sysfs_emit(buf, "%s%s%s%s%s%s%s\n", + return sysfs_emit(buf, "%s%s%s%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled], ibpb_state(), boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? "; IBRS_FW" : "", stibp_state(), boot_cpu_has(X86_FEATURE_RSB_CTXSW) ? "; RSB filling" : "", pbrsb_eibrs_state(), + spectre_bhi_state(), + /* this should always be at the end */ spectre_v2_module_string()); }