[PATCH 4/6] x86/virt/tdx: Sanity check the size of each metadata field

[Xu Yilun <yilun.xu@linux.intel.com>]

Add the build-time check to ensure the manually input field mappings
have consistent size definitions. I.e. for each mapping entry, the size
code in field_id should match the corresponding struct member type. This
type safe check prevents wrong interpretation of the readout value.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Kai Huang <kai.huang@intel.com>
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>
---
 arch/x86/virt/vmx/tdx/tdx_global_metadata.c | 24 ++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
index 3db87c4accd6..836d97166a7a 100644
--- a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
+++ b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
@@ -13,10 +13,32 @@ struct field_mapping {
 	int size;
 };
 
+/*
+ * Size of field abstracted from field ID.
+ *
+ * See Table "MD_FIELD_ID (Metadata Field Identifier / Sequence Header)
+ * Definition", TDX module 1.5 ABI spec.
+ *
+ *  - Bit 33:32: ELEMENT_SIZE_CODE -- size of a single element of metadata
+ *
+ *	0: 8 bits
+ *	1: 16 bits
+ *	2: 32 bits
+ *	3: 64 bits
+ */
+#define MD_FIELD_SIZE_CODE(_field_id)	\
+	(((_field_id) & GENMASK_ULL(33, 32)) >> 32)
+
+#define MD_FIELD_SIZE(_field_id) (1 << MD_FIELD_SIZE_CODE(_field_id))
+
+#define TD_SYSINFO_CHECK_SIZE(_field_id, _size)		\
+	__builtin_choose_expr(MD_FIELD_SIZE(_field_id) == (_size), _size, (void)0)
+
 #define TD_SYSINFO_MAP(_field_id, _member)				\
 	{ .field_id = _field_id,					\
 	  .offset = offsetof(struct tdx_sys_info, _member),		\
-	  .size = sizeof_field(struct tdx_sys_info, _member) }
+	  .size = TD_SYSINFO_CHECK_SIZE(_field_id,			\
+					sizeof_field(struct tdx_sys_info, _member)) }
 
 /* Map TD_SYSINFO fields into 'struct tdx_sys_info': */
 static const struct field_mapping mappings[] = {
-- 
2.25.1