From 4b708ea4e5e772747b89619489ab96e9d1a1a44d Mon Sep 17 00:00:00 2001 From: Pawan Gupta Date: Wed, 23 Oct 2019 11:01:53 +0200 Subject: x86/cpu: Add a "tsx=" cmdline option with TSX disabled by default commit 95c5824f75f3ba4c9e8e5a4b1a623c95390ac266 upstream. Add a kernel cmdline parameter "tsx" to control the Transactional Synchronization Extensions (TSX) feature. On CPUs that support TSX control, use "tsx=on|off" to enable or disable TSX. Not specifying this option is equivalent to "tsx=off". This is because on certain processors TSX may be used as a part of a speculative side channel attack. Carve out the TSX controlling functionality into a separate compilation unit because TSX is a CPU feature while the TSX async abort control machinery will go to cpu/bugs.c. [ bp: - Massage, shorten and clear the arg buffer. - Clarifications of the tsx= possible options - Josh. - Expand on TSX_CTRL availability - Pawan. ] Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner Reviewed-by: Josh Poimboeuf Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/tsx.c | 125 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 125 insertions(+) create mode 100644 arch/x86/kernel/cpu/tsx.c (limited to 'arch/x86/kernel/cpu/tsx.c') diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c new file mode 100644 index 000000000000..04471c4378d8 --- /dev/null +++ b/arch/x86/kernel/cpu/tsx.c @@ -0,0 +1,125 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Intel Transactional Synchronization Extensions (TSX) control. + * + * Copyright (C) 2019 Intel Corporation + * + * Author: + * Pawan Gupta + */ + +#include + +#include + +#include "cpu.h" + +enum tsx_ctrl_states tsx_ctrl_state __ro_after_init = TSX_CTRL_NOT_SUPPORTED; + +void tsx_disable(void) +{ + u64 tsx; + + rdmsrl(MSR_IA32_TSX_CTRL, tsx); + + /* Force all transactions to immediately abort */ + tsx |= TSX_CTRL_RTM_DISABLE; + + /* + * Ensure TSX support is not enumerated in CPUID. + * This is visible to userspace and will ensure they + * do not waste resources trying TSX transactions that + * will always abort. + */ + tsx |= TSX_CTRL_CPUID_CLEAR; + + wrmsrl(MSR_IA32_TSX_CTRL, tsx); +} + +void tsx_enable(void) +{ + u64 tsx; + + rdmsrl(MSR_IA32_TSX_CTRL, tsx); + + /* Enable the RTM feature in the cpu */ + tsx &= ~TSX_CTRL_RTM_DISABLE; + + /* + * Ensure TSX support is enumerated in CPUID. + * This is visible to userspace and will ensure they + * can enumerate and use the TSX feature. + */ + tsx &= ~TSX_CTRL_CPUID_CLEAR; + + wrmsrl(MSR_IA32_TSX_CTRL, tsx); +} + +static bool __init tsx_ctrl_is_supported(void) +{ + u64 ia32_cap = x86_read_arch_cap_msr(); + + /* + * TSX is controlled via MSR_IA32_TSX_CTRL. However, support for this + * MSR is enumerated by ARCH_CAP_TSX_MSR bit in MSR_IA32_ARCH_CAPABILITIES. + * + * TSX control (aka MSR_IA32_TSX_CTRL) is only available after a + * microcode update on CPUs that have their MSR_IA32_ARCH_CAPABILITIES + * bit MDS_NO=1. CPUs with MDS_NO=0 are not planned to get + * MSR_IA32_TSX_CTRL support even after a microcode update. Thus, + * tsx= cmdline requests will do nothing on CPUs without + * MSR_IA32_TSX_CTRL support. + */ + return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR); +} + +void __init tsx_init(void) +{ + char arg[4] = {}; + int ret; + + if (!tsx_ctrl_is_supported()) + return; + + ret = cmdline_find_option(boot_command_line, "tsx", arg, sizeof(arg)); + if (ret >= 0) { + if (!strcmp(arg, "on")) { + tsx_ctrl_state = TSX_CTRL_ENABLE; + } else if (!strcmp(arg, "off")) { + tsx_ctrl_state = TSX_CTRL_DISABLE; + } else { + tsx_ctrl_state = TSX_CTRL_DISABLE; + pr_err("tsx: invalid option, defaulting to off\n"); + } + } else { + /* tsx= not provided, defaulting to off */ + tsx_ctrl_state = TSX_CTRL_DISABLE; + } + + if (tsx_ctrl_state == TSX_CTRL_DISABLE) { + tsx_disable(); + + /* + * tsx_disable() will change the state of the + * RTM CPUID bit. Clear it here since it is now + * expected to be not set. + */ + setup_clear_cpu_cap(X86_FEATURE_RTM); + } else if (tsx_ctrl_state == TSX_CTRL_ENABLE) { + + /* + * HW defaults TSX to be enabled at bootup. + * We may still need the TSX enable support + * during init for special cases like + * kexec after TSX is disabled. + */ + tsx_enable(); + + /* + * tsx_enable() will change the state of the + * RTM CPUID bit. Force it here since it is now + * expected to be set. + */ + setup_force_cpu_cap(X86_FEATURE_RTM); + } +} -- cgit v1.2.3 From 8c99df217f8e36fde46cbf2af50b5b191857d9d4 Mon Sep 17 00:00:00 2001 From: Pawan Gupta Date: Wed, 23 Oct 2019 12:28:57 +0200 Subject: x86/tsx: Add "auto" option to the tsx= cmdline parameter commit 7531a3596e3272d1f6841e0d601a614555dc6b65 upstream. Platforms which are not affected by X86_BUG_TAA may want the TSX feature enabled. Add "auto" option to the TSX cmdline parameter. When tsx=auto disable TSX when X86_BUG_TAA is present, otherwise enable TSX. More details on X86_BUG_TAA can be found here: https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html [ bp: Extend the arg buffer to accommodate "auto\0". ] Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner Reviewed-by: Tony Luck Reviewed-by: Josh Poimboeuf Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/tsx.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'arch/x86/kernel/cpu/tsx.c') diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c index 04471c4378d8..dda328ec2ba1 100644 --- a/arch/x86/kernel/cpu/tsx.c +++ b/arch/x86/kernel/cpu/tsx.c @@ -75,7 +75,7 @@ static bool __init tsx_ctrl_is_supported(void) void __init tsx_init(void) { - char arg[4] = {}; + char arg[5] = {}; int ret; if (!tsx_ctrl_is_supported()) @@ -87,6 +87,11 @@ void __init tsx_init(void) tsx_ctrl_state = TSX_CTRL_ENABLE; } else if (!strcmp(arg, "off")) { tsx_ctrl_state = TSX_CTRL_DISABLE; + } else if (!strcmp(arg, "auto")) { + if (boot_cpu_has_bug(X86_BUG_TAA)) + tsx_ctrl_state = TSX_CTRL_DISABLE; + else + tsx_ctrl_state = TSX_CTRL_ENABLE; } else { tsx_ctrl_state = TSX_CTRL_DISABLE; pr_err("tsx: invalid option, defaulting to off\n"); -- cgit v1.2.3 From aa6ca7b9a9b72eb61e43f44c978dd8e6d4b2f046 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 23 Oct 2019 12:35:50 +0200 Subject: x86/tsx: Add config options to set tsx=on|off|auto commit db616173d787395787ecc93eef075fa975227b10 upstream. There is a general consensus that TSX usage is not largely spread while the history shows there is a non trivial space for side channel attacks possible. Therefore the tsx is disabled by default even on platforms that might have a safe implementation of TSX according to the current knowledge. This is a fair trade off to make. There are, however, workloads that really do benefit from using TSX and updating to a newer kernel with TSX disabled might introduce a noticeable regressions. This would be especially a problem for Linux distributions which will provide TAA mitigations. Introduce config options X86_INTEL_TSX_MODE_OFF, X86_INTEL_TSX_MODE_ON and X86_INTEL_TSX_MODE_AUTO to control the TSX feature. The config setting can be overridden by the tsx cmdline options. [ bp: Text cleanups from Josh. ] Suggested-by: Borislav Petkov Signed-off-by: Michal Hocko Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner Reviewed-by: Josh Poimboeuf Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/tsx.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) (limited to 'arch/x86/kernel/cpu/tsx.c') diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c index dda328ec2ba1..3e20d322bc98 100644 --- a/arch/x86/kernel/cpu/tsx.c +++ b/arch/x86/kernel/cpu/tsx.c @@ -73,6 +73,14 @@ static bool __init tsx_ctrl_is_supported(void) return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR); } +static enum tsx_ctrl_states x86_get_tsx_auto_mode(void) +{ + if (boot_cpu_has_bug(X86_BUG_TAA)) + return TSX_CTRL_DISABLE; + + return TSX_CTRL_ENABLE; +} + void __init tsx_init(void) { char arg[5] = {}; @@ -88,17 +96,19 @@ void __init tsx_init(void) } else if (!strcmp(arg, "off")) { tsx_ctrl_state = TSX_CTRL_DISABLE; } else if (!strcmp(arg, "auto")) { - if (boot_cpu_has_bug(X86_BUG_TAA)) - tsx_ctrl_state = TSX_CTRL_DISABLE; - else - tsx_ctrl_state = TSX_CTRL_ENABLE; + tsx_ctrl_state = x86_get_tsx_auto_mode(); } else { tsx_ctrl_state = TSX_CTRL_DISABLE; pr_err("tsx: invalid option, defaulting to off\n"); } } else { - /* tsx= not provided, defaulting to off */ - tsx_ctrl_state = TSX_CTRL_DISABLE; + /* tsx= not provided */ + if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO)) + tsx_ctrl_state = x86_get_tsx_auto_mode(); + else if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF)) + tsx_ctrl_state = TSX_CTRL_DISABLE; + else + tsx_ctrl_state = TSX_CTRL_ENABLE; } if (tsx_ctrl_state == TSX_CTRL_DISABLE) { -- cgit v1.2.3