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file.go
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file.go
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package efi
import (
"bytes"
"encoding/binary"
"fmt"
"github.com/golang/glog"
)
// FirmwareFileHeader as per EFI standard.
type FirmwareFileHeader struct {
GUID GUID
// ChecksumHeader is recalculated when Serialize is called.
ChecksumHeader uint8
// ChecksumData is recalculated when Serialize is called.
ChecksumData uint8
FileType FileType
Attributes uint8
// Size is recalculated when Serialize is called.
Size Uint24
State uint8
}
type FileType uint8
const (
FileTypeSecurityCore FileType = 3
FileTypePEICore FileType = 4
FileTypeDXECore FileType = 5
FileTypeDriver FileType = 7
FileTypeApplication FileType = 9
FileTypePadding FileType = 240
)
func (f FileType) String() string {
switch f {
case FileTypeSecurityCore:
return "security core"
case FileTypePEICore:
return "pei core"
case FileTypeDXECore:
return "dxe core"
case FileTypeDriver:
return "driver"
case FileTypeApplication:
return "application"
case FileTypePadding:
return "padding"
default:
return fmt.Sprintf("UNKNOWN(%d)", f)
}
}
// FirmwareFile represents an EFI Firmware File within a Firmware Volume.
type FirmwareFile struct {
FirmwareFileHeader
Sections []Section
// ReadOffset is the offset within the volume at which the file has been
// encountered.
ReadOffset int
}
func (f *FirmwareFile) Serialize() ([]byte, error) {
var data []byte
var err error
if f.FileType == FileTypePadding {
data = bytes.Repeat([]byte{0xff}, int(f.Size.Uint32()-0x18))
} else {
data, err = concatSections(f.Sections)
if err != nil {
return nil, fmt.Errorf("could not serialize sections: %w", err)
}
}
f.Size = ToUint24(uint32(len(data)) + 0x18)
f.ChecksumHeader = 0
f.ChecksumData = 0
state := f.State
f.State = 0
checkBuf := bytes.NewBuffer(nil)
binary.Write(checkBuf, binary.LittleEndian, f.FirmwareFileHeader)
f.ChecksumHeader = checksum8(checkBuf.Bytes())
if (f.Attributes & 0x40) != 0 {
f.ChecksumData = checksum8(data)
} else {
f.ChecksumData = 0x5a
}
f.State = state
buf := bytes.NewBuffer(nil)
if err := binary.Write(buf, binary.LittleEndian, f.FirmwareFileHeader); err != nil {
return nil, err
}
if _, err := buf.Write(data); err != nil {
panic(err)
}
return buf.Bytes(), nil
}
func readFile(r *NestedReader) (*FirmwareFile, error) {
start := r.TellGlobal()
var header FirmwareFileHeader
if err := binary.Read(r, binary.LittleEndian, &header); err != nil {
return nil, err
}
glog.V(1).Infof("File header @%08x: %+v", start, header)
size := header.Size.Uint32()
dataSub := r.Sub(0, int(size-0x18))
r.Advance(int(size - 0x18))
alignment := (size - 0x18) % 8
if alignment != 0 {
r.Advance(int(8 - alignment))
}
var sections []Section
if header.FileType != FileTypePadding {
var err error
sections, err = readSections(dataSub)
if err != nil {
return nil, err
}
}
// TODO: checksum
return &FirmwareFile{
FirmwareFileHeader: header,
Sections: sections,
ReadOffset: start,
}, nil
}