4.18-stable review patch. If anyone has any objections, please let me know.
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From: Jiri Kosina jkosina@suse.cz
Introduce the 'l1tf=' kernel command line option to allow for boot-time switching of mitigation that is used on processors affected by L1TF.
The possible values are:
full Provides all available mitigations for the L1TF vulnerability. Disables SMT and enables all mitigations in the hypervisors. SMT control via /sys/devices/system/cpu/smt/control is still possible after boot. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled.
full,force Same as 'full', but disables SMT control. Implies the 'nosmt=force' command line option. sysfs control of SMT and the hypervisor flush control is disabled.
flush Leaves SMT enabled and enables the conditional hypervisor mitigation. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled.
flush,nosmt Disables SMT and enables the conditional hypervisor mitigation. SMT control via /sys/devices/system/cpu/smt/control is still possible after boot. If SMT is reenabled or flushing disabled at runtime hypervisors will issue a warning.
flush,nowarn Same as 'flush', but hypervisors will not warn when a VM is started in a potentially insecure configuration.
off Disables hypervisor mitigations and doesn't emit any warnings.
Default is 'flush'.
Let KVM adhere to these semantics, which means:
- 'lt1f=full,force' : Performe L1D flushes. No runtime control possible.
- 'l1tf=full' - 'l1tf-flush' - 'l1tf=flush,nosmt' : Perform L1D flushes and warn on VM start if SMT has been runtime enabled or L1D flushing has been run-time enabled
- 'l1tf=flush,nowarn' : Perform L1D flushes and no warnings are emitted.
- 'l1tf=off' : L1D flushes are not performed and no warnings are emitted.
KVM can always override the L1D flushing behavior using its 'vmentry_l1d_flush' module parameter except when lt1f=full,force is set.
This makes KVM's private 'nosmt' option redundant, and as it is a bit non-systematic anyway (this is something to control globally, not on hypervisor level), remove that option.
Add the missing Documentation entry for the l1tf vulnerability sysfs file while at it.
Signed-off-by: Jiri Kosina jkosina@suse.cz Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Jiri Kosina jkosina@suse.cz Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Reviewed-by: Josh Poimboeuf jpoimboe@redhat.com Link: https://lkml.kernel.org/r/20180713142323.202758176@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/ABI/testing/sysfs-devices-system-cpu | 4 + Documentation/admin-guide/kernel-parameters.txt | 68 +++++++++++++++++++-- arch/x86/include/asm/processor.h | 12 +++ arch/x86/kernel/cpu/bugs.c | 44 +++++++++++++ arch/x86/kvm/vmx.c | 56 +++++++++++++---- 5 files changed, 165 insertions(+), 19 deletions(-)
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -476,6 +476,7 @@ What: /sys/devices/system/cpu/vulnerabi /sys/devices/system/cpu/vulnerabilities/spectre_v1 /sys/devices/system/cpu/vulnerabilities/spectre_v2 /sys/devices/system/cpu/vulnerabilities/spec_store_bypass + /sys/devices/system/cpu/vulnerabilities/l1tf Date: January 2018 Contact: Linux kernel mailing list linux-kernel@vger.kernel.org Description: Information about CPU vulnerabilities @@ -488,6 +489,9 @@ Description: Information about CPU vulne "Vulnerable" CPU is affected and no mitigation in effect "Mitigation: $M" CPU is affected and mitigation $M is in effect
+ Details about the l1tf file can be found in + Documentation/admin-guide/l1tf.rst + What: /sys/devices/system/cpu/smt /sys/devices/system/cpu/smt/active /sys/devices/system/cpu/smt/control --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1946,12 +1946,6 @@ [KVM,ARM] Allow use of GICv4 for direct injection of LPIs.
- kvm-intel.nosmt=[KVM,Intel] If the L1TF CPU bug is present (CVE-2018-3620) - 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) @@ -1989,6 +1983,68 @@ feature (tagged TLBs) on capable Intel chips. Default is 1 (enabled)
+ l1tf= [X86] Control mitigation of the L1TF vulnerability on + affected CPUs + + The kernel PTE inversion protection is unconditionally + enabled and cannot be disabled. + + full + Provides all available mitigations for the + L1TF vulnerability. Disables SMT and + enables all mitigations in the + hypervisors, i.e. unconditional L1D flush. + + SMT control and L1D flush control via the + sysfs interface is still possible after + boot. Hypervisors will issue a warning + when the first VM is started in a + potentially insecure configuration, + i.e. SMT enabled or L1D flush disabled. + + full,force + Same as 'full', but disables SMT and L1D + flush runtime control. Implies the + 'nosmt=force' command line option. + (i.e. sysfs control of SMT is disabled.) + + flush + Leaves SMT enabled and enables the default + hypervisor mitigation, i.e. conditional + L1D flush. + + SMT control and L1D flush control via the + sysfs interface is still possible after + boot. Hypervisors will issue a warning + when the first VM is started in a + potentially insecure configuration, + i.e. SMT enabled or L1D flush disabled. + + flush,nosmt + + Disables SMT and enables the default + hypervisor mitigation. + + SMT control and L1D flush control via the + sysfs interface is still possible after + boot. Hypervisors will issue a warning + when the first VM is started in a + potentially insecure configuration, + i.e. SMT enabled or L1D flush disabled. + + flush,nowarn + Same as 'flush', but hypervisors will not + warn when a VM is started in a potentially + insecure configuration. + + off + Disables hypervisor mitigations and doesn't + emit any warnings. + + Default is 'flush'. + + For details see: Documentation/admin-guide/l1tf.rst + l2cr= [PPC]
l3cr= [PPC] --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -982,4 +982,16 @@ bool xen_set_default_idle(void); void stop_this_cpu(void *dummy); void df_debug(struct pt_regs *regs, long error_code); void microcode_check(void); + +enum l1tf_mitigations { + L1TF_MITIGATION_OFF, + L1TF_MITIGATION_FLUSH_NOWARN, + L1TF_MITIGATION_FLUSH, + L1TF_MITIGATION_FLUSH_NOSMT, + L1TF_MITIGATION_FULL, + L1TF_MITIGATION_FULL_FORCE +}; + +extern enum l1tf_mitigations l1tf_mitigation; + #endif /* _ASM_X86_PROCESSOR_H */ --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -644,7 +644,11 @@ void x86_spec_ctrl_setup_ap(void) #undef pr_fmt #define pr_fmt(fmt) "L1TF: " fmt
+/* Default mitigation for L1TF-affected CPUs */ +enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH; #if IS_ENABLED(CONFIG_KVM_INTEL) +EXPORT_SYMBOL_GPL(l1tf_mitigation); + enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO; EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation); #endif @@ -656,6 +660,20 @@ static void __init l1tf_select_mitigatio if (!boot_cpu_has_bug(X86_BUG_L1TF)) return;
+ switch (l1tf_mitigation) { + case L1TF_MITIGATION_OFF: + case L1TF_MITIGATION_FLUSH_NOWARN: + case L1TF_MITIGATION_FLUSH: + break; + case L1TF_MITIGATION_FLUSH_NOSMT: + case L1TF_MITIGATION_FULL: + cpu_smt_disable(false); + break; + case L1TF_MITIGATION_FULL_FORCE: + cpu_smt_disable(true); + break; + } + #if CONFIG_PGTABLE_LEVELS == 2 pr_warn("Kernel not compiled for PAE. No mitigation for L1TF\n"); return; @@ -674,6 +692,32 @@ static void __init l1tf_select_mitigatio
setup_force_cpu_cap(X86_FEATURE_L1TF_PTEINV); } + +static int __init l1tf_cmdline(char *str) +{ + if (!boot_cpu_has_bug(X86_BUG_L1TF)) + return 0; + + if (!str) + return -EINVAL; + + if (!strcmp(str, "off")) + l1tf_mitigation = L1TF_MITIGATION_OFF; + else if (!strcmp(str, "flush,nowarn")) + l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOWARN; + else if (!strcmp(str, "flush")) + l1tf_mitigation = L1TF_MITIGATION_FLUSH; + else if (!strcmp(str, "flush,nosmt")) + l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT; + else if (!strcmp(str, "full")) + l1tf_mitigation = L1TF_MITIGATION_FULL; + else if (!strcmp(str, "full,force")) + l1tf_mitigation = L1TF_MITIGATION_FULL_FORCE; + + return 0; +} +early_param("l1tf", l1tf_cmdline); + #undef pr_fmt
#ifdef CONFIG_SYSFS --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -71,9 +71,6 @@ static const struct x86_cpu_id vmx_cpu_i }; 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);
@@ -215,15 +212,31 @@ static int vmx_setup_l1d_flush(enum vmx_ { struct page *page;
- /* If set to 'auto' select 'cond' */ - if (l1tf == VMENTER_L1D_FLUSH_AUTO) - l1tf = VMENTER_L1D_FLUSH_COND; - if (!enable_ept) { l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_EPT_DISABLED; return 0; }
+ /* If set to auto use the default l1tf mitigation method */ + if (l1tf == VMENTER_L1D_FLUSH_AUTO) { + switch (l1tf_mitigation) { + case L1TF_MITIGATION_OFF: + l1tf = VMENTER_L1D_FLUSH_NEVER; + break; + case L1TF_MITIGATION_FLUSH_NOWARN: + case L1TF_MITIGATION_FLUSH: + case L1TF_MITIGATION_FLUSH_NOSMT: + l1tf = VMENTER_L1D_FLUSH_COND; + break; + case L1TF_MITIGATION_FULL: + case L1TF_MITIGATION_FULL_FORCE: + l1tf = VMENTER_L1D_FLUSH_ALWAYS; + break; + } + } else if (l1tf_mitigation == L1TF_MITIGATION_FULL_FORCE) { + l1tf = VMENTER_L1D_FLUSH_ALWAYS; + } + if (l1tf != VMENTER_L1D_FLUSH_NEVER && !vmx_l1d_flush_pages && !boot_cpu_has(X86_FEATURE_FLUSH_L1D)) { page = alloc_pages(GFP_KERNEL, L1D_CACHE_ORDER); @@ -10604,19 +10617,36 @@ free_vcpu: return ERR_PTR(err); }
-#define L1TF_MSG "SMT enabled with L1TF CPU bug present. Refer to CVE-2018-3620 for details.\n" +#define L1TF_MSG_SMT "L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html for details.\n" +#define L1TF_MSG_L1D "L1TF CPU bug present and virtualization mitigation disabled, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html for details.\n"
static int vmx_vm_init(struct kvm *kvm) { if (!ple_gap) kvm->arch.pause_in_guest = true;
- if (boot_cpu_has(X86_BUG_L1TF) && cpu_smt_control == CPU_SMT_ENABLED) { - if (nosmt) { - pr_err(L1TF_MSG); - return -EOPNOTSUPP; + if (boot_cpu_has(X86_BUG_L1TF) && enable_ept) { + switch (l1tf_mitigation) { + case L1TF_MITIGATION_OFF: + case L1TF_MITIGATION_FLUSH_NOWARN: + /* 'I explicitly don't care' is set */ + break; + case L1TF_MITIGATION_FLUSH: + case L1TF_MITIGATION_FLUSH_NOSMT: + case L1TF_MITIGATION_FULL: + /* + * Warn upon starting the first VM in a potentially + * insecure environment. + */ + if (cpu_smt_control == CPU_SMT_ENABLED) + pr_warn_once(L1TF_MSG_SMT); + if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_NEVER) + pr_warn_once(L1TF_MSG_L1D); + break; + case L1TF_MITIGATION_FULL_FORCE: + /* Flush is enforced */ + break; } - pr_warn(L1TF_MSG); } return 0; }