On systems that have virtualization disabled or KVM module is not
loaded, sysfs mitigation state of X86_BUG_ITLB_MULTIHIT is reported
incorrectly as:
$ cat /sys/devices/system/cpu/vulnerabilities/itlb_multihit
KVM: Vulnerable
System is not vulnerable to DoS attack from a rogue guest when:
- KVM module is not loaded or
- Virtualization is disabled in the hardware or
- Kernel was configured without support for KVM
Change the reporting to "Currently not affected (KVM not in use)" for
such cases.
Reported-by: Nelson Dsouza <nelson.dsouza@xxxxxxxxxxxxxxx>
Fixes: b8e8c8303ff2 ("kvm: mmu: ITLB_MULTIHIT mitigation")
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
---
.../admin-guide/hw-vuln/multihit.rst | 5 +++-
arch/x86/include/asm/processor.h | 6 +++++
arch/x86/kernel/cpu/bugs.c | 24 +++++++++----------
arch/x86/kvm/mmu/mmu.c | 9 +++++--
4 files changed, 29 insertions(+), 15 deletions(-)
diff --git a/Documentation/admin-guide/hw-vuln/multihit.rst b/Documentation/admin-guide/hw-vuln/multihit.rst
index ba9988d8bce5..842961419f3e 100644
--- a/Documentation/admin-guide/hw-vuln/multihit.rst
+++ b/Documentation/admin-guide/hw-vuln/multihit.rst
@@ -82,7 +82,10 @@ The possible values in this file are:
- Software changes mitigate this issue.
* - KVM: Vulnerable
- The processor is vulnerable, but no mitigation enabled
-
+ * - Currently not affected (KVM not in use)
+ - The processor is vulnerable but no mitigation is required because
+ KVM module is not loaded or virtualization is disabled in the hardware or
+ kernel was configured without support for KVM.
Enumeration of the erratum
--------------------------------
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 03b7c4ca425a..830a3e7725af 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -989,4 +989,10 @@ enum mds_mitigations {
MDS_MITIGATION_VMWERV,
};
+enum itlb_multihit_mitigations {
+ ITLB_MULTIHIT_MITIGATION_OFF,
+ ITLB_MULTIHIT_MITIGATION_FULL,
+ ITLB_MULTIHIT_MITIGATION_NO_KVM,
+};
+
#endif /* _ASM_X86_PROCESSOR_H */
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0b71970d2d3d..97f66a93f2be 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1395,8 +1395,15 @@ void x86_spec_ctrl_setup_ap(void)
x86_amd_ssb_disable();
}
-bool itlb_multihit_kvm_mitigation;
-EXPORT_SYMBOL_GPL(itlb_multihit_kvm_mitigation);
+/* Default to KVM not in use, KVM module changes this later */
+enum itlb_multihit_mitigations itlb_multihit_mitigation = ITLB_MULTIHIT_MITIGATION_NO_KVM;
+EXPORT_SYMBOL_GPL(itlb_multihit_mitigation);
+
+static const char * const itlb_multihit_strings[] = {
+ [ITLB_MULTIHIT_MITIGATION_OFF] = "KVM: Vulnerable",
+ [ITLB_MULTIHIT_MITIGATION_FULL] = "KVM: Mitigation: Split huge pages",
+ [ITLB_MULTIHIT_MITIGATION_NO_KVM] = "Currently not affected (KVM not in use)",
+};
#undef pr_fmt
#define pr_fmt(fmt) "L1TF: " fmt
@@ -1553,25 +1560,18 @@ static ssize_t l1tf_show_state(char *buf)
l1tf_vmx_states[l1tf_vmx_mitigation],
sched_smt_active() ? "vulnerable" : "disabled");
}
-
-static ssize_t itlb_multihit_show_state(char *buf)
-{
- if (itlb_multihit_kvm_mitigation)
- return sprintf(buf, "KVM: Mitigation: Split huge pages\n");
- else
- return sprintf(buf, "KVM: Vulnerable\n");
-}
#else
static ssize_t l1tf_show_state(char *buf)
{
return sprintf(buf, "%s\n", L1TF_DEFAULT_MSG);
}
+#endif
static ssize_t itlb_multihit_show_state(char *buf)
{
- return sprintf(buf, "Processor vulnerable\n");
+ return sprintf(buf, "%s\n",
+ itlb_multihit_strings[itlb_multihit_mitigation]);
}
-#endif
static ssize_t mds_show_state(char *buf)
{
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6d6a0ae7800c..e089b9e565a5 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -50,7 +50,7 @@
#include <asm/kvm_page_track.h>
#include "trace.h"
-extern bool itlb_multihit_kvm_mitigation;
+extern enum itlb_multihit_mitigations itlb_multihit_mitigation;
static int __read_mostly nx_huge_pages = -1;
#ifdef CONFIG_PREEMPT_RT
@@ -6158,7 +6158,12 @@ static bool get_nx_auto_mode(void)
static void __set_nx_huge_pages(bool val)
{
- nx_huge_pages = itlb_multihit_kvm_mitigation = val;
+ nx_huge_pages = val;
+
+ if (val)
+ itlb_multihit_mitigation = ITLB_MULTIHIT_MITIGATION_FULL;
+ else
+ itlb_multihit_mitigation = ITLB_MULTIHIT_MITIGATION_OFF;
}
static int set_nx_huge_pages(const char *val, const struct kernel_param *kp)
--
2.21.3
