From: Konrad Rzeszutek Wilk Date: Wed, 20 Jun 2018 15:29:53 +0000 (-0400) Subject: x86/KVM: Warn user if KVM is loaded SMT and L1TF CPU bug being present X-Git-Tag: v4.1.12-124.31.3~641 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=a1d558a006c3b47182fd7b86961523da9e72d2da;p=users%2Fjedix%2Flinux-maple.git x86/KVM: Warn user if KVM is loaded SMT and L1TF CPU bug being present If the L1TF CPU bug is present we allow the KVM module to be loaded as the major of users that use Linux and KVM have trusted guests and do not want a broken setup. Cloud vendors are the ones that are uncomfortable with CVE 2018-3620 and as such they are the ones that should set nosmt to one. Setting 'nosmt' means that the system administrator also needs to disable SMT (Hyper-threading) in the BIOS, or via the 'nosmt' command line parameter, or via the /sys/devices/system/cpu/smt/control. See commit 05736e4ac13c ("cpu/hotplug: Provide knobs to control SMT"). Other mitigations are to use task affinity, cpu sets, interrupt binding, etc - anything to make sure that _only_ the same guests vCPUs are running on sibling threads. Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Thomas Gleixner Orabug: 28220674 CVE: CVE-2018-3646 (cherry picked from commit 26acfb666a473d960f0fd971fe68f3e3ad16c70b) Signed-off-by: Mihai Carabas Reviewed-by: Darren Kenny Reviewed-by: Boris Ostrovsky Conflicts: Documentation/admin-guide/kernel-parameters.txt arch/x86/kvm/vmx.c kernel/cpu.c Contextual: different content; This commit needs 03543133 "KVM: x86: Introducing kvm_x86_ops VM init/destroy hooks" --- diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index dfc5b1a9cbbc..8b21d64d91b1 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1714,6 +1714,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. for all guests. Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. + kvm-intel.nosmt=[KVM,Intel] If the L1TF CPU bug is present (CVE-2018-3646) + and the system has SMT (aka Hyper-Threading) enabled then + don't allow guests to be created. + + Default is 0 (allow guests to be created). + kvm-intel.ept= [KVM,Intel] Disable extended page tables (virtualized MMU) support on capable Intel chips. Default is 1 (enabled) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 4b1b99b5a68c..29ca44ade753 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -66,6 +66,9 @@ static const struct x86_cpu_id vmx_cpu_id[] = { }; MODULE_DEVICE_TABLE(x86cpu, vmx_cpu_id); +static bool __read_mostly nosmt; +module_param(nosmt, bool, S_IRUGO); + static bool __read_mostly enable_vpid = 1; module_param_named(vpid, enable_vpid, bool, 0444); @@ -8574,6 +8577,20 @@ free_vcpu: return ERR_PTR(err); } +#define L1TF_MSG "SMT enabled with L1TF CPU bug present. Refer to CVE-2018-3646 for details.\n" + +static int vmx_vm_init(struct kvm *kvm) +{ + if (boot_cpu_has(X86_BUG_L1TF) && cpu_smt_control == CPU_SMT_ENABLED) { + if (nosmt) { + pr_err(L1TF_MSG); + return -EOPNOTSUPP; + } + pr_warn(L1TF_MSG); + } + return 0; +} + static void __init vmx_check_processor_compat(void *rtn) { struct vmcs_config vmcs_conf; @@ -10328,6 +10345,8 @@ static struct kvm_x86_ops vmx_x86_ops = { .cpu_has_accelerated_tpr = report_flexpriority, .has_emulated_msr = vmx_has_emulated_msr, + .vm_init = vmx_vm_init, + .vcpu_create = vmx_create_vcpu, .vcpu_free = vmx_free_vcpu, .vcpu_reset = vmx_vcpu_reset, diff --git a/kernel/cpu.c b/kernel/cpu.c index 0383a1eee12e..2e6cac10e8e0 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -497,6 +497,7 @@ void __cpuinit smpboot_thread_init(void) #ifdef CONFIG_HOTPLUG_SMT enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED; +EXPORT_SYMBOL_GPL(cpu_smt_control); static int __init smt_cmdline_disable(char *str) {