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Dynamically size ESP partition to support images > 512MB #12

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20 changes: 13 additions & 7 deletions internal/gpt.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,21 +5,20 @@ import (
"crypto/sha512"
"encoding/binary"
"hash/crc32"
"math"
)

// Disk size constants
const (
diskSizeBytes = 1024 * 1024 * 1024 // 1GB
diskSizeSectors = diskSizeBytes / 512
partitionName = "esp"
mib = 1024 * 1024
gib = 1024 * mib
partitionName = "esp"
)

// LBA (Logical Block Address) constants
const (
gptHeaderLBA = 1
partitionEntryLBA = 2
espStartingLBA = 2048
espEndingLBA = 1026047
)

// GUID constants for disk and partition
Expand All @@ -28,8 +27,15 @@ const (
espPartitionGUID = "87654321-4321-8765-4321-876543218765"
)

// Generates the deterministic UEFI disk GUID hash for TDX measurements
func calculateUEFIDiskGUIDHash() []byte {
// Generates the deterministic UEFI disk GUID hash for TDX measurements.
// Sizes are derived from the EFI file size in the same way as mkosi.postoutput
func calculateUEFIDiskGUIDHash(efiSize int) []byte {
// Compute partition geometry to match systemd-repart + sgdisk behavior
espBytes := int(math.Ceil(float64(efiSize+32*mib)/4096)) * 4096 // repart rounds SizeMaxBytes up to 4096
diskBytes := int(math.Ceil(float64(espBytes+mib)/float64(gib))) * gib
diskSizeSectors := uint64(diskBytes / 512)
espEndingLBA := uint64(espStartingLBA + espBytes/512 - 1)

// GPT Header at LBA 1
header := struct {
Signature [8]byte
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2 changes: 1 addition & 1 deletion internal/mr.go
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Original file line number Diff line number Diff line change
Expand Up @@ -256,7 +256,7 @@ func MeasureRTMR1And2(kernelData []byte, initrdData []byte, kernelCmdline string
rtmr1Log := [][]byte{
measureSha384([]byte("Calling EFI Application from Boot Option")),
measureSha384([]byte{0x00, 0x00, 0x00, 0x00}), // Separator.
calculateUEFIDiskGUIDHash(),
calculateUEFIDiskGUIDHash(len(kernelData)),
ukiAuthHash.Hash(crypto.SHA384),
kernelAuthHash.Hash(crypto.SHA384),
measureSha384([]byte("Exit Boot Services Invocation")),
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