KVM: x86: Check for host supported fields in shadow vmcs

We track shadow vmcs fields through two static lists,
one for read only and another for r/w fields. However, with
addition of new vmcs fields, not all fields may be supported on
all hosts. If so, copy_vmcs12_to_shadow() trying to vmwrite on
unsupported hosts will result in a vmwrite error. For example, commit
36be0b9deb23161 introduced GUEST_BNDCFGS, which is not supported
by all processors. Filter out host unsupported fields before
letting guests use shadow vmcs

Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 41 insertions, 12 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1f68c5831924..33e8c028842f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -503,7 +503,7 @@ static inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)
                                 [number##_HIGH] = VMCS12_OFFSET(name)+4
 
 
-static const unsigned long shadow_read_only_fields[] = {
+static unsigned long shadow_read_only_fields[] = {
         /*
          * We do NOT shadow fields that are modified when L0
          * traps and emulates any vmx instruction (e.g. VMPTRLD,
@@ -526,10 +526,10 @@ static const unsigned long shadow_read_only_fields[] = {
         GUEST_LINEAR_ADDRESS,
         GUEST_PHYSICAL_ADDRESS
 };
-static const int max_shadow_read_only_fields =
+static int max_shadow_read_only_fields =
         ARRAY_SIZE(shadow_read_only_fields);
 
-static const unsigned long shadow_read_write_fields[] = {
+static unsigned long shadow_read_write_fields[] = {
         GUEST_RIP,
         GUEST_RSP,
         GUEST_CR0,
@@ -558,7 +558,7 @@ static const unsigned long shadow_read_write_fields[] = {
         HOST_FS_SELECTOR,
         HOST_GS_SELECTOR
 };
-static const int max_shadow_read_write_fields =
+static int max_shadow_read_write_fields =
         ARRAY_SIZE(shadow_read_write_fields);
 
 static const unsigned short vmcs_field_to_offset_table[] = {
@@ -3009,6 +3009,41 @@ static void free_kvm_area(void)
         }
 }
 
+static void init_vmcs_shadow_fields(void)
+{
+        int i, j;
+
+        /* No checks for read only fields yet */
+
+        for (i = j = 0; i < max_shadow_read_write_fields; i++) {
+                switch (shadow_read_write_fields[i]) {
+                case GUEST_BNDCFGS:
+                        if (!vmx_mpx_supported())
+                                continue;
+                        break;
+                default:
+                        break;
+                }
+
+                if (j < i)
+                        shadow_read_write_fields[j] =
+                                shadow_read_write_fields[i];
+                j++;
+        }
+        max_shadow_read_write_fields = j;
+
+        /* shadowed fields guest access without vmexit */
+        for (i = 0; i < max_shadow_read_write_fields; i++) {
+                clear_bit(shadow_read_write_fields[i],
+                          vmx_vmwrite_bitmap);
+                clear_bit(shadow_read_write_fields[i],
+                          vmx_vmread_bitmap);
+        }
+        for (i = 0; i < max_shadow_read_only_fields; i++)
+                clear_bit(shadow_read_only_fields[i],
+                          vmx_vmread_bitmap);
+}
+
 static __init int alloc_kvm_area(void)
 {
         int cpu;
@@ -3039,6 +3074,8 @@ static __init int hardware_setup(void)
                 enable_vpid = 0;
         if (!cpu_has_vmx_shadow_vmcs())
                 enable_shadow_vmcs = 0;
+        if (enable_shadow_vmcs)
+                init_vmcs_shadow_fields();
 
         if (!cpu_has_vmx_ept() ||
             !cpu_has_vmx_ept_4levels()) {
@@ -8803,14 +8840,6 @@ static int __init vmx_init(void)
 
         memset(vmx_vmread_bitmap, 0xff, PAGE_SIZE);
         memset(vmx_vmwrite_bitmap, 0xff, PAGE_SIZE);
-        /* shadowed read/write fields */
-        for (i = 0; i < max_shadow_read_write_fields; i++) {
-                clear_bit(shadow_read_write_fields[i], vmx_vmwrite_bitmap);
-                clear_bit(shadow_read_write_fields[i], vmx_vmread_bitmap);
-        }
-        /* shadowed read only fields */
-        for (i = 0; i < max_shadow_read_only_fields; i++)
-                clear_bit(shadow_read_only_fields[i], vmx_vmread_bitmap);
 
         /*
          * Allow direct access to the PC debug port (it is often used for I/O