fix(fw_cfg): clear ACPI table checksums before recalculation

alioth/src/board/board_x86_64/board_x86_64.rs

@@ -435,6 +435,7 @@ where
         if self.config.coco.is_none() {
             let ram = memory.ram_bus();
             acpi_table.relocate(EBDA_START + size_of::<AcpiTableRsdp>() as u64);
+            acpi_table.update_checksums();
             ram.write_range(
                 EBDA_START,
                 size_of::<AcpiTableRsdp>() as u64,

alioth/src/device/fw_cfg/acpi.rs

@@ -87,6 +87,7 @@ fn create_acpi_table_checksum(offset: usize, len: usize) -> AddChecksum {
 
 pub fn create_acpi_loader(mut acpi_table: AcpiTable) -> [FwCfgItem; 3] {
     acpi_table.relocate(0);
+    acpi_table.clear_checksums();
     let mut table_loader_bytes: Vec<u8> = Vec::new();
     let allocate_rsdp = Allocate {
         command: COMMAND_ALLOCATE,

alioth/src/firmware/acpi/acpi.rs

@@ -210,16 +210,18 @@ impl AcpiTable {
         let old_addr: u64 = transmute!(self.rsdp.xsdt_physical_address);
         self.rsdp.xsdt_physical_address = transmute!(table_addr);
 
-        let sum = wrapping_sum(&self.rsdp.as_bytes()[0..20]);
-        self.rsdp.checksum = self.rsdp.checksum.wrapping_sub(sum);
-        let ext_sum = wrapping_sum(self.rsdp.as_bytes());
-        self.rsdp.extended_checksum = self.rsdp.extended_checksum.wrapping_sub(ext_sum);
-
         for pointer in self.table_pointers.iter() {
             let (old_val, _) = u64::read_from_prefix(&self.tables[*pointer..]).unwrap();
             let new_val = old_val.wrapping_sub(old_addr).wrapping_add(table_addr);
             IntoBytes::write_to_prefix(&new_val, &mut self.tables[*pointer..]).unwrap();
         }
+    }
+
+    pub fn update_checksums(&mut self) {
+        let sum = wrapping_sum(&self.rsdp.as_bytes()[0..20]);
+        self.rsdp.checksum = self.rsdp.checksum.wrapping_sub(sum);
+        let ext_sum = wrapping_sum(self.rsdp.as_bytes());
+        self.rsdp.extended_checksum = self.rsdp.extended_checksum.wrapping_sub(ext_sum);
 
         for (start, len) in self.table_checksums.iter() {
             let sum = wrapping_sum(&self.tables[*start..(*start + *len)]);
@@ -228,6 +230,15 @@ impl AcpiTable {
         }
     }
 
+    pub fn clear_checksums(&mut self) {
+        for (start, _) in self.table_checksums.iter() {
+            let checksum = &mut self.tables[start + offset_of!(AcpiTableHeader, checksum)];
+            *checksum = 0;
+        }
+        self.rsdp.checksum = 0;
+        self.rsdp.extended_checksum = 0;
+    }
+
     pub fn rsdp(&self) -> &AcpiTableRsdp {
         &self.rsdp
     }