[acpi] Compute and check checksum for ACPI tables

Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/acpi.c

@@ -42,19 +42,41 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  ******************************************************************************
  */
 
+/**
+ * Compute ACPI table checksum
+ *
+ * @v table		Any ACPI table
+ * @ret checksum	0 if checksum is good
+ */
+static uint8_t acpi_checksum ( userptr_t table ) {
+	struct acpi_header acpi;
+	uint8_t sum = 0;
+	uint8_t data;
+	unsigned int i;
+
+	/* Read table length */
+	copy_from_user ( &acpi.length, table,
+			 offsetof ( typeof ( acpi ), length ),
+			 sizeof ( acpi.length ) );
+
+	/* Compute checksum */
+	for ( i = 0 ; i < le32_to_cpu ( acpi.length ) ; i++ ) {
+		copy_from_user ( &data, table, i, sizeof ( data ) );
+		sum += data;
+	}
+
+	return sum;
+}
+
 /**
  * Fix up ACPI table checksum
  *
  * @v acpi		ACPI table header
  */
 void acpi_fix_checksum ( struct acpi_header *acpi ) {
-	unsigned int i = 0;
-	uint8_t sum = 0;
 
-	for ( i = 0 ; i < acpi->length ; i++ ) {
-		sum += *( ( ( uint8_t * ) acpi ) + i );
-	}
-	acpi->checksum -= sum;
+	/* Update checksum */
+	acpi->checksum -= acpi_checksum ( virt_to_user ( acpi ) );
 }
 
 /**
@@ -123,6 +145,15 @@ userptr_t acpi_find ( uint32_t signature, unsigned int index ) {
 		if ( index-- )
 			continue;
 
+		/* Check table integrity */
+		if ( acpi_checksum ( table ) != 0 ) {
+			DBGC ( rsdt, "RSDT %#08lx found %s with bad checksum "
+			       "at %08lx\n", user_to_phys ( rsdt, 0 ),
+			       acpi_name ( signature ),
+			       user_to_phys ( table, 0 ) );
+			break;
+		}
+
 		DBGC ( rsdt, "RSDT %#08lx found %s at %08lx\n",
 		       user_to_phys ( rsdt, 0 ), acpi_name ( signature ),
 		       user_to_phys ( table, 0 ) );