From db616173d787395787ecc93eef075fa975227b10 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 23 Oct 2019 12:35:50 +0200 Subject: [PATCH] x86/tsx: Add config options to set tsx=on|off|auto 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 --- arch/x86/Kconfig | 45 +++++++++++++++++++++++++++++++++++++++ arch/x86/kernel/cpu/tsx.c | 22 +++++++++++++------ 2 files changed, 61 insertions(+), 6 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index d6e1faa28c58..8ef85139553f 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1940,6 +1940,51 @@ config X86_INTEL_MEMORY_PROTECTION_KEYS If unsure, say y. +choice + prompt "TSX enable mode" + depends on CPU_SUP_INTEL + default X86_INTEL_TSX_MODE_OFF + help + Intel's TSX (Transactional Synchronization Extensions) feature + allows to optimize locking protocols through lock elision which + can lead to a noticeable performance boost. + + On the other hand it has been shown that TSX can be exploited + to form side channel attacks (e.g. TAA) and chances are there + will be more of those attacks discovered in the future. + + Therefore TSX is not enabled by default (aka tsx=off). An admin + might override this decision by tsx=on the command line parameter. + Even with TSX enabled, the kernel will attempt to enable the best + possible TAA mitigation setting depending on the microcode available + for the particular machine. + + This option allows to set the default tsx mode between tsx=on, =off + and =auto. See Documentation/admin-guide/kernel-parameters.txt for more + details. + + Say off if not sure, auto if TSX is in use but it should be used on safe + platforms or on if TSX is in use and the security aspect of tsx is not + relevant. + +config X86_INTEL_TSX_MODE_OFF + bool "off" + help + TSX is disabled if possible - equals to tsx=off command line parameter. + +config X86_INTEL_TSX_MODE_ON + bool "on" + help + TSX is always enabled on TSX capable HW - equals the tsx=on command + line parameter. + +config X86_INTEL_TSX_MODE_AUTO + bool "auto" + help + TSX is enabled on TSX capable HW that is believed to be safe against + side channel attacks- equals the tsx=auto command line parameter. +endchoice + config EFI bool "EFI runtime service support" depends on ACPI 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) { -- GitLab