diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2022-04-17 19:55:59 +0300 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-04-17 19:55:59 +0300 |
commit | 3a69a44278a72e15f12e24f5db4d277a497649aa (patch) | |
tree | d062707ff3a248b8dcbec40be4c62779fcf11592 /arch/x86 | |
parent | fbb9c58e56f2ee56e77b19fdfac131d57d3341c1 (diff) | |
parent | 400331f8ffa3bec5c561417e5eec6848464e9160 (diff) | |
download | linux-3a69a44278a72e15f12e24f5db4d277a497649aa.tar.xz |
Merge tag 'x86-urgent-2022-04-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fixes from Thomas Gleixner:
"Two x86 fixes related to TSX:
- Use either MSR_TSX_FORCE_ABORT or MSR_IA32_TSX_CTRL to disable TSX
to cover all CPUs which allow to disable it.
- Disable TSX development mode at boot so that a microcode update
which provides TSX development mode does not suddenly make the
system vulnerable to TSX Asynchronous Abort"
* tag 'x86-urgent-2022-04-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/tsx: Disable TSX development mode at boot
x86/tsx: Use MSR_TSX_CTRL to clear CPUID bits
Diffstat (limited to 'arch/x86')
-rw-r--r-- | arch/x86/include/asm/msr-index.h | 4 | ||||
-rw-r--r-- | arch/x86/kernel/cpu/common.c | 2 | ||||
-rw-r--r-- | arch/x86/kernel/cpu/cpu.h | 5 | ||||
-rw-r--r-- | arch/x86/kernel/cpu/intel.c | 7 | ||||
-rw-r--r-- | arch/x86/kernel/cpu/tsx.c | 104 |
5 files changed, 100 insertions, 22 deletions
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 0eb90d21049e..ee15311b6be1 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -128,9 +128,9 @@ #define TSX_CTRL_RTM_DISABLE BIT(0) /* Disable RTM feature */ #define TSX_CTRL_CPUID_CLEAR BIT(1) /* Disable TSX enumeration */ -/* SRBDS support */ #define MSR_IA32_MCU_OPT_CTRL 0x00000123 -#define RNGDS_MITG_DIS BIT(0) +#define RNGDS_MITG_DIS BIT(0) /* SRBDS support */ +#define RTM_ALLOW BIT(1) /* TSX development mode */ #define MSR_IA32_SYSENTER_CS 0x00000174 #define MSR_IA32_SYSENTER_ESP 0x00000175 diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index ed4417500700..e342ae4db3c4 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1855,6 +1855,8 @@ void identify_secondary_cpu(struct cpuinfo_x86 *c) validate_apic_and_package_id(c); x86_spec_ctrl_setup_ap(); update_srbds_msr(); + + tsx_ap_init(); } static __init int setup_noclflush(char *arg) diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h index ee6f23f7587d..2a8e584fc991 100644 --- a/arch/x86/kernel/cpu/cpu.h +++ b/arch/x86/kernel/cpu/cpu.h @@ -55,11 +55,10 @@ enum tsx_ctrl_states { extern __ro_after_init enum tsx_ctrl_states tsx_ctrl_state; extern void __init tsx_init(void); -extern void tsx_enable(void); -extern void tsx_disable(void); -extern void tsx_clear_cpuid(void); +void tsx_ap_init(void); #else static inline void tsx_init(void) { } +static inline void tsx_ap_init(void) { } #endif /* CONFIG_CPU_SUP_INTEL */ extern void get_cpu_cap(struct cpuinfo_x86 *c); diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 8321c43554a1..f7a5370a9b3b 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -717,13 +717,6 @@ static void init_intel(struct cpuinfo_x86 *c) init_intel_misc_features(c); - if (tsx_ctrl_state == TSX_CTRL_ENABLE) - tsx_enable(); - else if (tsx_ctrl_state == TSX_CTRL_DISABLE) - tsx_disable(); - else if (tsx_ctrl_state == TSX_CTRL_RTM_ALWAYS_ABORT) - tsx_clear_cpuid(); - split_lock_init(); bus_lock_init(); diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c index 9c7a5f049292..ec7bbac3a9f2 100644 --- a/arch/x86/kernel/cpu/tsx.c +++ b/arch/x86/kernel/cpu/tsx.c @@ -19,7 +19,7 @@ enum tsx_ctrl_states tsx_ctrl_state __ro_after_init = TSX_CTRL_NOT_SUPPORTED; -void tsx_disable(void) +static void tsx_disable(void) { u64 tsx; @@ -39,7 +39,7 @@ void tsx_disable(void) wrmsrl(MSR_IA32_TSX_CTRL, tsx); } -void tsx_enable(void) +static void tsx_enable(void) { u64 tsx; @@ -58,7 +58,7 @@ void tsx_enable(void) wrmsrl(MSR_IA32_TSX_CTRL, tsx); } -static bool __init tsx_ctrl_is_supported(void) +static bool tsx_ctrl_is_supported(void) { u64 ia32_cap = x86_read_arch_cap_msr(); @@ -84,7 +84,45 @@ static enum tsx_ctrl_states x86_get_tsx_auto_mode(void) return TSX_CTRL_ENABLE; } -void tsx_clear_cpuid(void) +/* + * Disabling TSX is not a trivial business. + * + * First of all, there's a CPUID bit: X86_FEATURE_RTM_ALWAYS_ABORT + * which says that TSX is practically disabled (all transactions are + * aborted by default). When that bit is set, the kernel unconditionally + * disables TSX. + * + * In order to do that, however, it needs to dance a bit: + * + * 1. The first method to disable it is through MSR_TSX_FORCE_ABORT and + * the MSR is present only when *two* CPUID bits are set: + * + * - X86_FEATURE_RTM_ALWAYS_ABORT + * - X86_FEATURE_TSX_FORCE_ABORT + * + * 2. The second method is for CPUs which do not have the above-mentioned + * MSR: those use a different MSR - MSR_IA32_TSX_CTRL and disable TSX + * through that one. Those CPUs can also have the initially mentioned + * CPUID bit X86_FEATURE_RTM_ALWAYS_ABORT set and for those the same strategy + * applies: TSX gets disabled unconditionally. + * + * When either of the two methods are present, the kernel disables TSX and + * clears the respective RTM and HLE feature flags. + * + * An additional twist in the whole thing presents late microcode loading + * which, when done, may cause for the X86_FEATURE_RTM_ALWAYS_ABORT CPUID + * bit to be set after the update. + * + * A subsequent hotplug operation on any logical CPU except the BSP will + * cause for the supported CPUID feature bits to get re-detected and, if + * RTM and HLE get cleared all of a sudden, but, userspace did consult + * them before the update, then funny explosions will happen. Long story + * short: the kernel doesn't modify CPUID feature bits after booting. + * + * That's why, this function's call in init_intel() doesn't clear the + * feature flags. + */ +static void tsx_clear_cpuid(void) { u64 msr; @@ -97,6 +135,39 @@ void tsx_clear_cpuid(void) rdmsrl(MSR_TSX_FORCE_ABORT, msr); msr |= MSR_TFA_TSX_CPUID_CLEAR; wrmsrl(MSR_TSX_FORCE_ABORT, msr); + } else if (tsx_ctrl_is_supported()) { + rdmsrl(MSR_IA32_TSX_CTRL, msr); + msr |= TSX_CTRL_CPUID_CLEAR; + wrmsrl(MSR_IA32_TSX_CTRL, msr); + } +} + +/* + * Disable TSX development mode + * + * When the microcode released in Feb 2022 is applied, TSX will be disabled by + * default on some processors. MSR 0x122 (TSX_CTRL) and MSR 0x123 + * (IA32_MCU_OPT_CTRL) can be used to re-enable TSX for development, doing so is + * not recommended for production deployments. In particular, applying MD_CLEAR + * flows for mitigation of the Intel TSX Asynchronous Abort (TAA) transient + * execution attack may not be effective on these processors when Intel TSX is + * enabled with updated microcode. + */ +static void tsx_dev_mode_disable(void) +{ + u64 mcu_opt_ctrl; + + /* Check if RTM_ALLOW exists */ + if (!boot_cpu_has_bug(X86_BUG_TAA) || !tsx_ctrl_is_supported() || + !cpu_feature_enabled(X86_FEATURE_SRBDS_CTRL)) + return; + + rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_opt_ctrl); + + if (mcu_opt_ctrl & RTM_ALLOW) { + mcu_opt_ctrl &= ~RTM_ALLOW; + wrmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_opt_ctrl); + setup_force_cpu_cap(X86_FEATURE_RTM_ALWAYS_ABORT); } } @@ -105,14 +176,14 @@ void __init tsx_init(void) char arg[5] = {}; int ret; + tsx_dev_mode_disable(); + /* - * Hardware will always abort a TSX transaction if both CPUID bits - * RTM_ALWAYS_ABORT and TSX_FORCE_ABORT are set. In this case, it is - * better not to enumerate CPUID.RTM and CPUID.HLE bits. Clear them - * here. + * Hardware will always abort a TSX transaction when the CPUID bit + * RTM_ALWAYS_ABORT is set. In this case, it is better not to enumerate + * CPUID.RTM and CPUID.HLE bits. Clear them here. */ - if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT) && - boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT)) { + if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT)) { tsx_ctrl_state = TSX_CTRL_RTM_ALWAYS_ABORT; tsx_clear_cpuid(); setup_clear_cpu_cap(X86_FEATURE_RTM); @@ -175,3 +246,16 @@ void __init tsx_init(void) setup_force_cpu_cap(X86_FEATURE_HLE); } } + +void tsx_ap_init(void) +{ + tsx_dev_mode_disable(); + + if (tsx_ctrl_state == TSX_CTRL_ENABLE) + tsx_enable(); + else if (tsx_ctrl_state == TSX_CTRL_DISABLE) + tsx_disable(); + else if (tsx_ctrl_state == TSX_CTRL_RTM_ALWAYS_ABORT) + /* See comment over that function for more details. */ + tsx_clear_cpuid(); +} |