metropolis/pkg/efivarfs/boot.go - monogon - Gitiles

 // MIT License
 //
 // Copyright (c) 2021 Philippe Voinov (philippevoinov@gmail.com)
 // Copyright 2021 The Monogon Project Authors.
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
 // in the Software without restriction, including without limitation the rights
 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 // copies of the Software, and to permit persons to whom the Software is
 // furnished to do so, subject to the following conditions:
 //
 // The above copyright notice and this permission notice shall be included in all
 // copies or substantial portions of the Software.
 //
 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.

 package efivarfs

 import (
 	"fmt"
 	"math"
 	"strings"

 	"github.com/google/uuid"
 	"golang.org/x/text/transform"
 )

 // Note on binary format of EFI variables:
 // This code follows Section 3 "Boot Manager" of version 2.6 of the UEFI Spec:
 // http://www.uefi.org/sites/default/files/resources/UEFI%20Spec%202_6.pdf
 // It uses the binary representation from the Linux "efivars" filesystem.
 // Specifically, all binary data that is marshaled and unmarshaled is preceded by
 // 4 bytes of "Variable Attributes".
 // All binary data must have exactly the correct length and may not be padded
 // with extra bytes while reading or writing.

 // Note on EFI variable attributes:
 // This code ignores all EFI variable attributes when reading.
 // This code always writes variables with the following attributes:
 //   - EFI_VARIABLE_NON_VOLATILE (0x00000001)
 //   - EFI_VARIABLE_BOOTSERVICE_ACCESS (0x00000002)
 //   - EFI_VARIABLE_RUNTIME_ACCESS (0x00000004)
 const defaultAttrsByte0 uint8 = 7

 // BootEntry represents a subset of the contents of a Boot#### EFI variable.
 type BootEntry struct {
 	Description     string // eg. "Linux Boot Manager"
 	Path            string // eg. `\EFI\systemd\systemd-bootx64.efi`
 	PartitionGUID   uuid.UUID
 	PartitionNumber uint32 // Starts with 1
 	PartitionStart  uint64 // LBA
 	PartitionSize   uint64 // LBA
 }

 // Marshal generates the binary representation of a BootEntry (EFI_LOAD_OPTION).
 // Description, DiskGUID and Path must be set.
 // Attributes of the boot entry (EFI_LOAD_OPTION.Attributes, not the same
 // as attributes of an EFI variable) are always set to LOAD_OPTION_ACTIVE.
 func (t *BootEntry) Marshal() ([]byte, error) {
 	if t.Description == "" ||
 		t.PartitionGUID.String() == "00000000-0000-0000-0000-000000000000" ||
 		t.Path == "" ||
 		t.PartitionNumber == 0 ||
 		t.PartitionStart == 0 ||
 		t.PartitionSize == 0 {
 		return nil, fmt.Errorf("missing field, all are required: %+v", *t)
 	}

 	// EFI_LOAD_OPTION.FilePathList
 	var dp []byte

 	// EFI_LOAD_OPTION.FilePathList[0]
 	dp = append(dp,
 		0x04,       // Type ("Media Device Path")
 		0x01,       // Sub-Type ("Hard Drive")
 		0x2a, 0x00, // Length (always 42 bytes for this type)
 	)
 	dp = append32(dp, t.PartitionNumber)
 	dp = append64(dp, t.PartitionStart)
 	dp = append64(dp, t.PartitionSize)
 	// Append the partition GUID in the EFI format.
 	dp = append(dp, MarshalEFIGUID(t.PartitionGUID)...)

 	dp = append(dp,
 		0x02, // Partition Format ("GUID Partition Table")
 		0x02, // Signature Type ("GUID signature")
 	)

 	// EFI_LOAD_OPTION.FilePathList[1]
 	enc := Encoding.NewEncoder()
 	bsp := strings.ReplaceAll(t.Path, "/", "\\")
 	path, _, e := transform.Bytes(enc, []byte(bsp))
 	if e != nil {
 		return nil, fmt.Errorf("while encoding Path: %v", e)
 	}
 	path = append16(path, 0) // null terminate string
 	filePathLen := len(path) + 4
 	dp = append(dp,
 		0x04, // Type ("Media Device Path")
 		0x04, // Sub-Type ("File Path")
 	)
 	dp = append16(dp, uint16(filePathLen))
 	dp = append(dp, path...)

 	// EFI_LOAD_OPTION.FilePathList[2] ("Device Path End Structure")
 	dp = append(dp,
 		0x7F,       // Type ("End of Hardware Device Path")
 		0xFF,       // Sub-Type ("End Entire Device Path")
 		0x04, 0x00, // Length (always 4 bytes for this type)
 	)

 	out := []byte{
 		// EFI variable attributes
 		defaultAttrsByte0, 0x00, 0x00, 0x00,

 		// EFI_LOAD_OPTION.Attributes (only LOAD_OPTION_ACTIVE)
 		0x01, 0x00, 0x00, 0x00,
 	}

 	// EFI_LOAD_OPTION.FilePathListLength
 	if len(dp) > math.MaxUint16 {
 		// No need to also check for overflows for Path length field explicitly,
 		// since if that overflows, this field will definitely overflow as well.
 		// There is no explicit length field for Description, so no special
 		// handling is required.
 		return nil, fmt.Errorf("variable too large, use shorter strings")
 	}
 	out = append16(out, uint16(len(dp)))

 	// EFI_LOAD_OPTION.Description
 	desc, _, e := transform.Bytes(enc, []byte(t.Description))
 	if e != nil {
 		return nil, fmt.Errorf("while encoding Description: %v", e)
 	}
 	desc = append16(desc, 0) // null terminate string
 	out = append(out, desc...)

 	// EFI_LOAD_OPTION.FilePathList
 	out = append(out, dp...)

 	// EFI_LOAD_OPTION.OptionalData is always empty

 	return out, nil
 }

 // UnmarshalBootEntry loads a BootEntry from its binary representation.
 // WARNING: UnmarshalBootEntry only loads the Description field.
 // Everything else is ignored (and not validated if possible)
 func UnmarshalBootEntry(d []byte) (*BootEntry, error) {
 	descOffset := 4 /* EFI Var Attrs */ + 4 /* EFI_LOAD_OPTION.Attributes */ + 2 /*FilePathListLength*/
 	if len(d) < descOffset {
 		return nil, fmt.Errorf("too short: %v bytes", len(d))
 	}
 	descBytes := []byte{}
 	var foundNull bool
 	for i := descOffset; i+1 < len(d); i += 2 {
 		a := d[i]
 		b := d[i+1]
 		if a == 0 && b == 0 {
 			foundNull = true
 			break
 		}
 		descBytes = append(descBytes, a, b)
 	}
 	if !foundNull {
 		return nil, fmt.Errorf("didn't find null terminator for Description")
 	}
 	descDecoded, _, e := transform.Bytes(Encoding.NewDecoder(), descBytes)
 	if e != nil {
 		return nil, fmt.Errorf("while decoding Description: %v", e)
 	}
 	return &BootEntry{Description: string(descDecoded)}, nil
 }

 // BootOrder represents the contents of the BootOrder EFI variable.
 type BootOrder []uint16

 // Marshal generates the binary representation of a BootOrder.
 func (t *BootOrder) Marshal() []byte {
 	out := []byte{defaultAttrsByte0, 0x00, 0x00, 0x00}
 	for _, v := range *t {
 		out = append16(out, v)
 	}
 	return out
 }

 // UnmarshalBootOrder loads a BootOrder from its binary representation.
 func UnmarshalBootOrder(d []byte) (*BootOrder, error) {
 	if len(d) < 4 || len(d)%2 != 0 {
 		return nil, fmt.Errorf("invalid length: %v bytes", len(d))
 	}
 	l := (len(d) - 4) / 2
 	out := make(BootOrder, l)
 	for i := 0; i < l; i++ {
 		out[i] = uint16(d[4+2*i]) | uint16(d[4+2*i+1])<<8
 	}
 	return &out, nil
 }

 func append16(d []byte, v uint16) []byte {
 	return append(d,
 		byte(v&0xFF),
 		byte(v>>8&0xFF),
 	)
 }

 func append32(d []byte, v uint32) []byte {
 	return append(d,
 		byte(v&0xFF),
 		byte(v>>8&0xFF),
 		byte(v>>16&0xFF),
 		byte(v>>24&0xFF),
 	)
 }

 func append64(d []byte, v uint64) []byte {
 	return append(d,
 		byte(v&0xFF),
 		byte(v>>8&0xFF),
 		byte(v>>16&0xFF),
 		byte(v>>24&0xFF),
 		byte(v>>32&0xFF),
 		byte(v>>40&0xFF),
 		byte(v>>48&0xFF),
 		byte(v>>56&0xFF),
 	)
 }
	// MIT License
	//
	// Copyright (c) 2021 Philippe Voinov (philippevoinov@gmail.com)
	// Copyright 2021 The Monogon Project Authors.
	//
	// Permission is hereby granted, free of charge, to any person obtaining a copy
	// of this software and associated documentation files (the "Software"), to deal
	// in the Software without restriction, including without limitation the rights
	// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	// copies of the Software, and to permit persons to whom the Software is
	// furnished to do so, subject to the following conditions:
	//
	// The above copyright notice and this permission notice shall be included in all
	// copies or substantial portions of the Software.
	//
	// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	// SOFTWARE.

	package efivarfs

	import (
	"fmt"
	"math"
	"strings"

	"github.com/google/uuid"
	"golang.org/x/text/transform"
	)

	// Note on binary format of EFI variables:
	// This code follows Section 3 "Boot Manager" of version 2.6 of the UEFI Spec:
	// http://www.uefi.org/sites/default/files/resources/UEFI%20Spec%202_6.pdf
	// It uses the binary representation from the Linux "efivars" filesystem.
	// Specifically, all binary data that is marshaled and unmarshaled is preceded by
	// 4 bytes of "Variable Attributes".
	// All binary data must have exactly the correct length and may not be padded
	// with extra bytes while reading or writing.

	// Note on EFI variable attributes:
	// This code ignores all EFI variable attributes when reading.
	// This code always writes variables with the following attributes:
	// - EFI_VARIABLE_NON_VOLATILE (0x00000001)
	// - EFI_VARIABLE_BOOTSERVICE_ACCESS (0x00000002)
	// - EFI_VARIABLE_RUNTIME_ACCESS (0x00000004)
	const defaultAttrsByte0 uint8 = 7

	// BootEntry represents a subset of the contents of a Boot#### EFI variable.
	type BootEntry struct {
	Description string // eg. "Linux Boot Manager"
	Path string // eg. `\EFI\systemd\systemd-bootx64.efi`
	PartitionGUID uuid.UUID
	PartitionNumber uint32 // Starts with 1
	PartitionStart uint64 // LBA
	PartitionSize uint64 // LBA
	}

	// Marshal generates the binary representation of a BootEntry (EFI_LOAD_OPTION).
	// Description, DiskGUID and Path must be set.
	// Attributes of the boot entry (EFI_LOAD_OPTION.Attributes, not the same
	// as attributes of an EFI variable) are always set to LOAD_OPTION_ACTIVE.
	func (t *BootEntry) Marshal() ([]byte, error) {
	if t.Description == "" \|\|
	t.PartitionGUID.String() == "00000000-0000-0000-0000-000000000000" \|\|
	t.Path == "" \|\|
	t.PartitionNumber == 0 \|\|
	t.PartitionStart == 0 \|\|
	t.PartitionSize == 0 {
	return nil, fmt.Errorf("missing field, all are required: %+v", *t)
	}

	// EFI_LOAD_OPTION.FilePathList
	var dp []byte

	// EFI_LOAD_OPTION.FilePathList[0]
	dp = append(dp,
	0x04, // Type ("Media Device Path")
	0x01, // Sub-Type ("Hard Drive")
	0x2a, 0x00, // Length (always 42 bytes for this type)
	)
	dp = append32(dp, t.PartitionNumber)
	dp = append64(dp, t.PartitionStart)
	dp = append64(dp, t.PartitionSize)
	// Append the partition GUID in the EFI format.
	dp = append(dp, MarshalEFIGUID(t.PartitionGUID)...)

	dp = append(dp,
	0x02, // Partition Format ("GUID Partition Table")
	0x02, // Signature Type ("GUID signature")
	)

	// EFI_LOAD_OPTION.FilePathList[1]
	enc := Encoding.NewEncoder()
	bsp := strings.ReplaceAll(t.Path, "/", "\\")
	path, _, e := transform.Bytes(enc, []byte(bsp))
	if e != nil {
	return nil, fmt.Errorf("while encoding Path: %v", e)
	}
	path = append16(path, 0) // null terminate string
	filePathLen := len(path) + 4
	dp = append(dp,
	0x04, // Type ("Media Device Path")
	0x04, // Sub-Type ("File Path")
	)
	dp = append16(dp, uint16(filePathLen))
	dp = append(dp, path...)

	// EFI_LOAD_OPTION.FilePathList[2] ("Device Path End Structure")
	dp = append(dp,
	0x7F, // Type ("End of Hardware Device Path")
	0xFF, // Sub-Type ("End Entire Device Path")
	0x04, 0x00, // Length (always 4 bytes for this type)
	)

	out := []byte{
	// EFI variable attributes
	defaultAttrsByte0, 0x00, 0x00, 0x00,

	// EFI_LOAD_OPTION.Attributes (only LOAD_OPTION_ACTIVE)
	0x01, 0x00, 0x00, 0x00,
	}

	// EFI_LOAD_OPTION.FilePathListLength
	if len(dp) > math.MaxUint16 {
	// No need to also check for overflows for Path length field explicitly,
	// since if that overflows, this field will definitely overflow as well.
	// There is no explicit length field for Description, so no special
	// handling is required.
	return nil, fmt.Errorf("variable too large, use shorter strings")
	}
	out = append16(out, uint16(len(dp)))

	// EFI_LOAD_OPTION.Description
	desc, _, e := transform.Bytes(enc, []byte(t.Description))
	if e != nil {
	return nil, fmt.Errorf("while encoding Description: %v", e)
	}
	desc = append16(desc, 0) // null terminate string
	out = append(out, desc...)

	// EFI_LOAD_OPTION.FilePathList
	out = append(out, dp...)

	// EFI_LOAD_OPTION.OptionalData is always empty

	return out, nil
	}

	// UnmarshalBootEntry loads a BootEntry from its binary representation.
	// WARNING: UnmarshalBootEntry only loads the Description field.
	// Everything else is ignored (and not validated if possible)
	func UnmarshalBootEntry(d []byte) (*BootEntry, error) {
	descOffset := 4 /* EFI Var Attrs / + 4 / EFI_LOAD_OPTION.Attributes / + 2 /FilePathListLength*/
	if len(d) < descOffset {
	return nil, fmt.Errorf("too short: %v bytes", len(d))
	}
	descBytes := []byte{}
	var foundNull bool
	for i := descOffset; i+1 < len(d); i += 2 {
	a := d[i]
	b := d[i+1]
	if a == 0 && b == 0 {
	foundNull = true
	break
	}
	descBytes = append(descBytes, a, b)
	}
	if !foundNull {
	return nil, fmt.Errorf("didn't find null terminator for Description")
	}
	descDecoded, _, e := transform.Bytes(Encoding.NewDecoder(), descBytes)
	if e != nil {
	return nil, fmt.Errorf("while decoding Description: %v", e)
	}
	return &BootEntry{Description: string(descDecoded)}, nil
	}

	// BootOrder represents the contents of the BootOrder EFI variable.
	type BootOrder []uint16

	// Marshal generates the binary representation of a BootOrder.
	func (t *BootOrder) Marshal() []byte {
	out := []byte{defaultAttrsByte0, 0x00, 0x00, 0x00}
	for _, v := range *t {
	out = append16(out, v)
	}
	return out
	}

	// UnmarshalBootOrder loads a BootOrder from its binary representation.
	func UnmarshalBootOrder(d []byte) (*BootOrder, error) {
	if len(d) < 4 \|\| len(d)%2 != 0 {
	return nil, fmt.Errorf("invalid length: %v bytes", len(d))
	}
	l := (len(d) - 4) / 2
	out := make(BootOrder, l)
	for i := 0; i < l; i++ {
	out[i] = uint16(d[4+2i]) \| uint16(d[4+2i+1])<<8
	}
	return &out, nil
	}

	func append16(d []byte, v uint16) []byte {
	return append(d,
	byte(v&0xFF),
	byte(v>>8&0xFF),
	)
	}

	func append32(d []byte, v uint32) []byte {
	return append(d,
	byte(v&0xFF),
	byte(v>>8&0xFF),
	byte(v>>16&0xFF),
	byte(v>>24&0xFF),
	)
	}

	func append64(d []byte, v uint64) []byte {
	return append(d,
	byte(v&0xFF),
	byte(v>>8&0xFF),
	byte(v>>16&0xFF),
	byte(v>>24&0xFF),
	byte(v>>32&0xFF),
	byte(v>>40&0xFF),
	byte(v>>48&0xFF),
	byte(v>>56&0xFF),
	)
	}