build/measurement/acpi: Compute memory offsets based on DSDT

build/measurement/acpi/acpi.go

@@ -5,25 +5,14 @@ import (
 	"embed"
 	"encoding/binary"
 	"encoding/hex"
-	"encoding/json"
 	"fmt"
 
 	"github.com/oasisprotocol/oasis-core/go/runtime/bundle"
 )
 
-//go:embed *.hex *.json
+//go:embed *.hex
 var templates embed.FS
 
-// OffsetData is the offset data file format.
-type OffsetData struct {
-	Memory MemoryOffsetData `json:"memory"`
-}
-
-type MemoryOffsetData struct {
-	RangeMinimumOffset int `json:"range_minimum_offset"`
-	LengthOffset       int `json:"length_offset"`
-}
-
 // GenerateTablesQemu generates ACPI tables for the given TD configuration.
 //
 // Returns the raw ACPI tables, RSDP and QEMU table loader command blob.
@@ -40,28 +29,6 @@ func GenerateTablesQemu(resources *bundle.TDXResources) ([]byte, []byte, []byte,
 		return nil, nil, nil, fmt.Errorf("malformed ACPI table template")
 	}
 
-	// Fetch corresponding offset data.
-	fn = fmt.Sprintf("template_qemu_cpu%d.json", resources.CPUCount)
-	offsetData, err := templates.ReadFile(fn)
-	if err != nil {
-		return nil, nil, nil, fmt.Errorf("offset data for ACPI tables is not available")
-	}
-
-	var od OffsetData
-	if err = json.Unmarshal(offsetData, &od); err != nil {
-		return nil, nil, nil, fmt.Errorf("malformed ACPI table offset data")
-	}
-
-	// Handle memory split at 2816 MiB (0xB0000000).
-	if resources.Memory >= 2816 {
-		binary.LittleEndian.PutUint32(tpl[od.Memory.RangeMinimumOffset:], 0x80000000)
-		binary.LittleEndian.PutUint32(tpl[od.Memory.LengthOffset:], 0x60000000)
-	} else {
-		memSizeBytes := uint32(resources.Memory * 1024 * 1024) //nolint: gosec
-		binary.LittleEndian.PutUint32(tpl[od.Memory.RangeMinimumOffset:], memSizeBytes)
-		binary.LittleEndian.PutUint32(tpl[od.Memory.LengthOffset:], 0xe0000000-memSizeBytes)
-	}
-
 	// Generate RSDP.
 	rsdp := append([]byte{},
 		0x52, 0x53, 0x44, 0x20, 0x50, 0x54, 0x52, 0x20, // Signature ("RSDP PTR ").
@@ -96,6 +63,19 @@ func GenerateTablesQemu(resources *bundle.TDXResources) ([]byte, []byte, []byte,
 		return nil, nil, nil, err
 	}
 
+	// Handle memory split at 2816 MiB (0xB0000000).
+	lengthOffset := dsdtLen - 684           // Offset of the length field inside the DSDT table.
+	rangeMinimumOffset := lengthOffset - 12 // Offset of the range minimum field inside the DSDT table.
+
+	if resources.Memory >= 2816 {
+		binary.LittleEndian.PutUint32(tpl[rangeMinimumOffset:], 0x80000000)
+		binary.LittleEndian.PutUint32(tpl[lengthOffset:], 0x60000000)
+	} else {
+		memSizeBytes := uint32(resources.Memory * 1024 * 1024) //nolint: gosec
+		binary.LittleEndian.PutUint32(tpl[rangeMinimumOffset:], memSizeBytes)
+		binary.LittleEndian.PutUint32(tpl[lengthOffset:], 0xe0000000-memSizeBytes)
+	}
+
 	// Update RSDP with RSDT address.
 	var rsdtAddress [4]byte
 	binary.LittleEndian.PutUint32(rsdtAddress[:], rsdtOffset)