4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jiri Kosina jkosina@suse.cz
commit 53c613fe6349994f023245519265999eed75957f upstream.
STIBP is a feature provided by certain Intel ucodes / CPUs. This feature (once enabled) prevents cross-hyperthread control of decisions made by indirect branch predictors.
Enable this feature if
- the CPU is vulnerable to spectre v2 - the CPU supports SMT and has SMT siblings online - spectre_v2 mitigation autoselection is enabled (default)
After some previous discussion, this leaves STIBP on all the time, as wrmsr on crossing kernel boundary is a no-no. This could perhaps later be a bit more optimized (like disabling it in NOHZ, experiment with disabling it in idle, etc) if needed.
Note that the synchronization of the mask manipulation via newly added spec_ctrl_mutex is currently not strictly needed, as the only updater is already being serialized by cpu_add_remove_lock, but let's make this a little bit more future-proof.
Signed-off-by: Jiri Kosina jkosina@suse.cz Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Peter Zijlstra peterz@infradead.org Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: "WoodhouseDavid" dwmw@amazon.co.uk Cc: Andi Kleen ak@linux.intel.com Cc: Tim Chen tim.c.chen@linux.intel.com Cc: "SchauflerCasey" casey.schaufler@intel.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/nycvar.YFH.7.76.1809251438240.15880@cbobk.fhfr.pm Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/cpu/bugs.c | 57 ++++++++++++++++++++++++++++++++++++++++----- kernel/cpu.c | 11 +++++++- 2 files changed, 61 insertions(+), 7 deletions(-)
--- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -35,12 +35,10 @@ static void __init spectre_v2_select_mit static void __init ssb_select_mitigation(void); static void __init l1tf_select_mitigation(void);
-/* - * Our boot-time value of the SPEC_CTRL MSR. We read it once so that any - * writes to SPEC_CTRL contain whatever reserved bits have been set. - */ -u64 __ro_after_init x86_spec_ctrl_base; +/* The base value of the SPEC_CTRL MSR that always has to be preserved. */ +u64 x86_spec_ctrl_base; EXPORT_SYMBOL_GPL(x86_spec_ctrl_base); +static DEFINE_MUTEX(spec_ctrl_mutex);
/* * The vendor and possibly platform specific bits which can be modified in @@ -324,6 +322,46 @@ static enum spectre_v2_mitigation_cmd __ return cmd; }
+static bool stibp_needed(void) +{ + if (spectre_v2_enabled == SPECTRE_V2_NONE) + return false; + + if (!boot_cpu_has(X86_FEATURE_STIBP)) + return false; + + return true; +} + +static void update_stibp_msr(void *info) +{ + wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); +} + +void arch_smt_update(void) +{ + u64 mask; + + if (!stibp_needed()) + return; + + mutex_lock(&spec_ctrl_mutex); + mask = x86_spec_ctrl_base; + if (cpu_smt_control == CPU_SMT_ENABLED) + mask |= SPEC_CTRL_STIBP; + else + mask &= ~SPEC_CTRL_STIBP; + + if (mask != x86_spec_ctrl_base) { + pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n", + cpu_smt_control == CPU_SMT_ENABLED ? + "Enabling" : "Disabling"); + x86_spec_ctrl_base = mask; + on_each_cpu(update_stibp_msr, NULL, 1); + } + mutex_unlock(&spec_ctrl_mutex); +} + static void __init spectre_v2_select_mitigation(void) { enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline(); @@ -408,6 +446,9 @@ retpoline_auto: setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW); pr_info("Enabling Restricted Speculation for firmware calls\n"); } + + /* Enable STIBP if appropriate */ + arch_smt_update(); }
#undef pr_fmt @@ -798,6 +839,8 @@ static ssize_t l1tf_show_state(char *buf static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr, char *buf, unsigned int bug) { + int ret; + if (!boot_cpu_has_bug(bug)) return sprintf(buf, "Not affected\n");
@@ -815,10 +858,12 @@ static ssize_t cpu_show_common(struct de return sprintf(buf, "Mitigation: __user pointer sanitization\n");
case X86_BUG_SPECTRE_V2: - return sprintf(buf, "%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled], + ret = sprintf(buf, "%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled], boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB" : "", boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "", + (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "", spectre_v2_module_string()); + return ret;
case X86_BUG_SPEC_STORE_BYPASS: return sprintf(buf, "%s\n", ssb_strings[ssb_mode]); --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2033,6 +2033,12 @@ static void cpuhp_online_cpu_device(unsi kobject_uevent(&dev->kobj, KOBJ_ONLINE); }
+/* + * Architectures that need SMT-specific errata handling during SMT hotplug + * should override this. + */ +void __weak arch_smt_update(void) { }; + static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) { int cpu, ret = 0; @@ -2059,8 +2065,10 @@ static int cpuhp_smt_disable(enum cpuhp_ */ cpuhp_offline_cpu_device(cpu); } - if (!ret) + if (!ret) { cpu_smt_control = ctrlval; + arch_smt_update(); + } cpu_maps_update_done(); return ret; } @@ -2071,6 +2079,7 @@ static int cpuhp_smt_enable(void)
cpu_maps_update_begin(); cpu_smt_control = CPU_SMT_ENABLED; + arch_smt_update(); for_each_present_cpu(cpu) { /* Skip online CPUs and CPUs on offline nodes */ if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))