[Qemu-devel] [PATCH for-4.1? 2/2] vmstate.h: Type check VMSTATE_STRUCT_VARRAY macros

[Peter Maydell <peter.maydell@linaro.org>]

The VMSTATE_STRUCT_VARRAY_UINT32 macro is intended to handle
migrating a field which is an array of structs, but where instead of
migrating the entire array we only migrate a variable number of
elements of it.

The VMSTATE_STRUCT_VARRAY_POINTER_UINT32 macro is intended to handle
migrating a field which is of pointer type, and points to a
dynamically allocated array of structs of variable size.

We weren't actually checking that the field passed to
VMSTATE_STRUCT_VARRAY_UINT32 really is an array, with the result that
accidentally using it where the _POINTER_ macro was intended would
compile but silently corrupt memory on migration.

Add type-checking that enforces that the field passed in is
really of the right array type. This applies to all the VMSTATE
macros which use flags including VMS_VARRAY_* but not VMS_POINTER.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 include/migration/vmstate.h | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index ca68584eba4..2df333c3612 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -227,8 +227,19 @@ extern const VMStateInfo vmstate_info_bitmap;
 extern const VMStateInfo vmstate_info_qtailq;
 
 #define type_check_2darray(t1,t2,n,m) ((t1(*)[n][m])0 - (t2*)0)
+/* Check that t2 is an array of t1 of size n */
 #define type_check_array(t1,t2,n) ((t1(*)[n])0 - (t2*)0)
 #define type_check_pointer(t1,t2) ((t1**)0 - (t2*)0)
+/*
+ * type of element 0 of the specified (array) field of the type.
+ * Note that if the field is a pointer then this will return the
+ * pointed-to type rather than complaining.
+ */
+#define typeof_elt_of_field(type, field) typeof(((type *)0)->field[0])
+/* Check that field f in struct type t2 is an array of t1, of any size */
+#define type_check_varray(t1, t2, f)                                 \
+    (type_check(t1, typeof_elt_of_field(t2, f))                      \
+     + QEMU_BUILD_BUG_ON_ZERO(!QEMU_IS_ARRAY(((t2 *)0)->f)))
 
 #define vmstate_offset_value(_state, _field, _type)                  \
     (offsetof(_state, _field) +                                      \
@@ -253,6 +264,10 @@ extern const VMStateInfo vmstate_info_qtailq;
     vmstate_offset_array(_state, _field, uint8_t,                    \
                          sizeof(typeof_field(_state, _field)))
 
+#define vmstate_offset_varray(_state, _field, _type)                 \
+    (offsetof(_state, _field) +                                      \
+     type_check_varray(_type, _state, _field))
+
 /* In the macros below, if there is a _version, that means the macro's
  * field will be processed only if the version being received is >=
  * the _version specified.  In general, if you add a new field, you
@@ -347,7 +362,7 @@ extern const VMStateInfo vmstate_info_qtailq;
     .info       = &(_info),                                          \
     .size       = sizeof(_type),                                     \
     .flags      = VMS_VARRAY_UINT32|VMS_MULTIPLY_ELEMENTS,           \
-    .offset     = offsetof(_state, _field),                          \
+    .offset     = vmstate_offset_varray(_state, _field, _type),      \
 }
 
 #define VMSTATE_ARRAY_TEST(_field, _state, _num, _test, _info, _type) {\
@@ -376,7 +391,7 @@ extern const VMStateInfo vmstate_info_qtailq;
     .info       = &(_info),                                          \
     .size       = sizeof(_type),                                     \
     .flags      = VMS_VARRAY_INT32,                                  \
-    .offset     = offsetof(_state, _field),                          \
+    .offset     = vmstate_offset_varray(_state, _field, _type),      \
 }
 
 #define VMSTATE_VARRAY_INT32(_field, _state, _field_num, _version, _info, _type) {\
@@ -416,7 +431,7 @@ extern const VMStateInfo vmstate_info_qtailq;
     .info       = &(_info),                                          \
     .size       = sizeof(_type),                                     \
     .flags      = VMS_VARRAY_UINT16,                                 \
-    .offset     = offsetof(_state, _field),                          \
+    .offset     = vmstate_offset_varray(_state, _field, _type),      \
 }
 
 #define VMSTATE_VSTRUCT_TEST(_field, _state, _test, _version, _vmsd, _type, _struct_version) { \
@@ -520,7 +535,7 @@ extern const VMStateInfo vmstate_info_qtailq;
     .vmsd       = &(_vmsd),                                          \
     .size       = sizeof(_type),                                     \
     .flags      = VMS_STRUCT|VMS_VARRAY_UINT8,                       \
-    .offset     = offsetof(_state, _field),                          \
+    .offset     = vmstate_offset_varray(_state, _field, _type),      \
 }
 
 /* a variable length array (i.e. _type *_field) but we know the
@@ -573,7 +588,7 @@ extern const VMStateInfo vmstate_info_qtailq;
     .vmsd       = &(_vmsd),                                          \
     .size       = sizeof(_type),                                     \
     .flags      = VMS_STRUCT|VMS_VARRAY_INT32,                       \
-    .offset     = offsetof(_state, _field),                          \
+    .offset     = vmstate_offset_varray(_state, _field, _type),      \
 }
 
 #define VMSTATE_STRUCT_VARRAY_UINT32(_field, _state, _field_num, _version, _vmsd, _type) { \
@@ -583,7 +598,7 @@ extern const VMStateInfo vmstate_info_qtailq;
     .vmsd       = &(_vmsd),                                          \
     .size       = sizeof(_type),                                     \
     .flags      = VMS_STRUCT|VMS_VARRAY_UINT32,                      \
-    .offset     = offsetof(_state, _field),                          \
+    .offset     = vmstate_offset_varray(_state, _field, _type),      \
 }
 
 #define VMSTATE_STRUCT_VARRAY_ALLOC(_field, _state, _field_num, _version, _vmsd, _type) {\
-- 
2.20.1