[PATCH] KVM: x86: Check for host supported fields in shadow vmcs

[Bandan Das]

We track shadow vmcs fields through two static lists,
one for read only fields and another for r/w. 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 older
hosts will result in a vmwrite error. For example, commit
36be0b9deb23161 introduced GUEST_BNDCFGS, which is not supported
for all processors. Create new lists based out of intersection of
static lists and host support and use them for tracking
shadow fields instead

Signed-off-by: Bandan Das <bsd@xxxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 98 +++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 79 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 7bed3e3..ffc2232 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -502,7 +502,10 @@ static inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)
 #define FIELD64(number, name)	[number] = VMCS12_OFFSET(name), \
 				[number##_HIGH] = VMCS12_OFFSET(name)+4
 
-
+/*
+ * Do not use the two lists below directly
+ * Use vmcs_shadow_fields instead
+ */
 static const unsigned long shadow_read_only_fields[] = {
 	/*
 	 * We do NOT shadow fields that are modified when L0
@@ -526,8 +529,6 @@ static const unsigned long shadow_read_only_fields[] = {
 	GUEST_LINEAR_ADDRESS,
 	GUEST_PHYSICAL_ADDRESS
 };
-static const int max_shadow_read_only_fields =
-	ARRAY_SIZE(shadow_read_only_fields);
 
 static const unsigned long shadow_read_write_fields[] = {
 	GUEST_RIP,
@@ -558,8 +559,18 @@ static const unsigned long shadow_read_write_fields[] = {
 	HOST_FS_SELECTOR,
 	HOST_GS_SELECTOR
 };
-static const int max_shadow_read_write_fields =
-	ARRAY_SIZE(shadow_read_write_fields);
+
+/* If new shadow fields are added, these should be modified appropriately */
+#define VMCS_MAX_RO_FIELDS 10
+#define VMCS_MAX_RW_FIELDS 30
+
+struct vmcs_shadow_fields_data {
+	int shadow_ro_fields_len;
+	int shadow_rw_fields_len;
+	unsigned long shadow_read_only_fields[VMCS_MAX_RO_FIELDS];
+	unsigned long shadow_read_write_fields[VMCS_MAX_RW_FIELDS];
+};
+static struct vmcs_shadow_fields_data vmcs_shadow_fields;
 
 static const unsigned short vmcs_field_to_offset_table[] = {
 	FIELD(VIRTUAL_PROCESSOR_ID, virtual_processor_id),
@@ -3027,6 +3038,56 @@ static __init int alloc_kvm_area(void)
 	return 0;
 }
 
+static void cleanup_vmcs_shadow_fields(void)
+{
+	memset(&vmcs_shadow_fields, 0,
+	       sizeof(struct vmcs_shadow_fields_data));
+}
+
+static void init_vmcs_shadow_fields(void)
+{
+	struct vmcs_shadow_fields_data *vmcs_ptr = &vmcs_shadow_fields;
+	int max_shadow_read_write_fields = ARRAY_SIZE(shadow_read_write_fields);
+	int max_shadow_read_only_fields = ARRAY_SIZE(shadow_read_only_fields);
+	int i, j;
+
+	for (i = 0, j = 0; i < max_shadow_read_write_fields; i++) {
+		if (i >= VMCS_MAX_RW_FIELDS) {
+			WARN(1, "Shadow RW fields index out of bounds\n");
+			break;
+		}
+		if ((shadow_read_write_fields[i] == GUEST_BNDCFGS) &&
+		    !vmx_mpx_supported())
+			continue;
+		vmcs_ptr->shadow_read_write_fields[j++] =
+			shadow_read_write_fields[i];
+		vmcs_ptr->shadow_rw_fields_len++;
+	}
+
+	for (i = 0, j = 0; i < max_shadow_read_only_fields; i++) {
+		if (i >= VMCS_MAX_RO_FIELDS) {
+			WARN(1, "Shadow RO fields index out of bounds\n");
+			break;
+		}
+		vmcs_ptr->shadow_read_only_fields[j++] =
+			shadow_read_only_fields[i];
+		vmcs_ptr->shadow_ro_fields_len++;
+	}
+
+	/* shadowed read/write fields */
+	for (i = 0; i < vmcs_ptr->shadow_rw_fields_len; i++) {
+		clear_bit(vmcs_ptr->shadow_read_write_fields[i],
+			  vmx_vmwrite_bitmap);
+		clear_bit(vmcs_ptr->shadow_read_write_fields[i],
+			  vmx_vmread_bitmap);
+	}
+	/* shadowed read only fields */
+	for (i = 0; i < vmcs_ptr->shadow_ro_fields_len; i++)
+		clear_bit(vmcs_ptr->shadow_read_only_fields[i],
+			  vmx_vmread_bitmap);
+
+}
+
 static __init int hardware_setup(void)
 {
 	if (setup_vmcs_config(&vmcs_config) < 0)
@@ -3039,6 +3100,8 @@ 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()) {
@@ -3084,6 +3147,8 @@ static __init int hardware_setup(void)
 
 static __exit void hardware_unsetup(void)
 {
+	if (enable_shadow_vmcs)
+		cleanup_vmcs_shadow_fields();
 	free_kvm_area();
 }
 
@@ -6159,8 +6224,9 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx)
 	unsigned long field;
 	u64 field_value;
 	struct vmcs *shadow_vmcs = vmx->nested.current_shadow_vmcs;
-	const unsigned long *fields = shadow_read_write_fields;
-	const int num_fields = max_shadow_read_write_fields;
+	const unsigned long *fields =
+		vmcs_shadow_fields.shadow_read_write_fields;
+	const int num_fields = vmcs_shadow_fields.shadow_rw_fields_len;
 
 	vmcs_load(shadow_vmcs);
 
@@ -6189,13 +6255,15 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx)
 
 static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx)
 {
+	struct vmcs_shadow_fields_data *ptr = &vmcs_shadow_fields;
+
 	const unsigned long *fields[] = {
-		shadow_read_write_fields,
-		shadow_read_only_fields
+		ptr->shadow_read_write_fields,
+		ptr->shadow_read_only_fields
 	};
 	const int max_fields[] = {
-		max_shadow_read_write_fields,
-		max_shadow_read_only_fields
+		ptr->shadow_rw_fields_len,
+		ptr->shadow_ro_fields_len
 	};
 	int i, q;
 	unsigned long field;
@@ -8817,14 +8885,6 @@ 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
-- 
1.8.3.1

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