multiboot.go

// Copyright 2018-2019 the u-root Authors. All rights reserved
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package multiboot implements bootloading multiboot kernels as defined by
// https://www.gnu.org/software/grub/manual/multiboot/multiboot.html.
//
// Package multiboot crafts kexec segments that can be used with the kexec_load
// system call.
package multiboot

import (
	"bytes"
	"debug/elf"
	"encoding/binary"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"strings"

	"github.com/u-root/u-root/pkg/ibft"
	"github.com/u-root/u-root/pkg/kexec"
	"github.com/u-root/u-root/pkg/multiboot/internal/trampoline"
	"github.com/u-root/u-root/pkg/ubinary"
)

const bootloader = "u-root kexec"

// multiboot defines parameters for working with multiboot kernels.
type multiboot struct {
	mem kexec.Memory

	file    string
	modules []string

	cmdLine    string
	bootloader string

	// trampoline is a path to an executable blob, which contains a trampoline segment.
	// Trampoline sets machine to a specific state defined by multiboot v1 spec.
	// https://www.gnu.org/software/grub/manual/multiboot/multiboot.html#Machine-state.
	trampoline string

	header header

	// infoAddr is a pointer to multiboot info.
	infoAddr uintptr
	// kernelEntry is a pointer to entry point of kernel.
	kernelEntry uintptr
	// EntryPoint is a pointer to trampoline.
	entryPoint uintptr

	info          info
	loadedModules []module
}

var (
	rangeTypes = map[kexec.RangeType]uint32{
		kexec.RangeRAM:      1,
		kexec.RangeDefault:  2,
		kexec.RangeACPI:     3,
		kexec.RangeNVS:      4,
		kexec.RangeReserved: 2,
	}
	PageSize = os.Getpagesize()
)

var sizeofMemoryMap = uint(binary.Size(MemoryMap{}))

// MemoryMap represents a reserved range of memory passed via the multiboot Info header.
type MemoryMap struct {
	// Size is the size of the associated structure in bytes.
	Size uint32
	// BaseAddr is the starting address.
	BaseAddr uint64
	// Length is the size of the memory region in bytes.
	Length uint64
	// Type is the variety of address range represented.
	Type uint32
}

// String returns a readable representation of a MemoryMap entry.
func (m MemoryMap) String() string {
	return fmt.Sprintf("[0x%x, 0x%x) (len: 0x%x, size: 0x%x, type: %d)", m.BaseAddr, m.BaseAddr+m.Length, m.Length, m.Size, m.Type)
}

type memoryMaps []MemoryMap

// String returns a new-line-separated representation of the entire memory map.
func (m memoryMaps) String() string {
	var s []string
	for _, mm := range m {
		s = append(s, mm.String())
	}
	return strings.Join(s, "\n")
}

// Probe checks if file is multiboot v1 kernel.
func Probe(file string) error {
	b, err := readFile(file)
	if err != nil {
		return err
	}
	kernel := &kernelReader{buf: b}
	_, err = parseHeader(kernel)
	return err
}

// newMB returns a new multiboot instance.
func newMB(file, cmdLine string, modules []string) (*multiboot, error) {
	// Trampoline should be a part of current binary.
	p, err := os.Executable()
	if err != nil {
		return nil, fmt.Errorf("Cannot find current executable path: %v", err)
	}
	trampoline, err := filepath.EvalSymlinks(p)
	if err != nil {
		return nil, fmt.Errorf("Cannot eval symlinks for %v: %v", p, err)
	}

	return &multiboot{
		file:       file,
		modules:    modules,
		cmdLine:    cmdLine,
		trampoline: trampoline,
		bootloader: bootloader,
		mem:        kexec.Memory{},
	}, nil
}

// Load parses and loads a multiboot kernel `file` using kexec_load.
//
// Each module is a path followed by optional command-line arguments, e.g.
// []string{"./module arg1 arg2", "./module2 arg3 arg4"}.
//
// debug turns on debug logging.
//
// Load can set up an arbitrary number of modules, and takes care of the
// multiboot info structure, including the memory map.
//
// After Load is called, kexec.Reboot() is ready to be called any time to stop
// Linux and execute the loaded kernel.
func Load(debug bool, file, cmdline string, modules []string, ibft *ibft.IBFT) error {
	m, err := newMB(file, cmdline, modules)
	if err != nil {
		return err
	}
	if err := m.load(debug, ibft); err != nil {
		return err
	}
	if err := kexec.Load(m.entryPoint, m.mem.Segments, 0); err != nil {
		return fmt.Errorf("kexec.Load() error: %v", err)
	}
	return nil
}

// load loads and parses multiboot information from m.file.
func (m *multiboot) load(debug bool, ibft *ibft.IBFT) error {
	log.Printf("Parsing file %v", m.file)
	b, err := readFile(m.file)
	if err != nil {
		return err
	}
	kernel := kernelReader{buf: b}
	log.Println("Parsing multiboot header")
	if m.header, err = parseHeader(&kernel); err != nil {
		return fmt.Errorf("error parsing headers: %v", err)
	}

	log.Printf("Getting kernel entry point")
	if m.kernelEntry, err = getEntryPoint(kernel); err != nil {
		return fmt.Errorf("error getting kernel entry point: %v", err)
	}
	log.Printf("Kernel entry point at %#x", m.kernelEntry)

	log.Printf("Parsing ELF segments")
	if err := m.mem.LoadElfSegments(kernel); err != nil {
		return fmt.Errorf("error loading ELF segments: %v", err)
	}

	log.Printf("Parsing memory map")
	if err := m.mem.ParseMemoryMap(); err != nil {
		return fmt.Errorf("error parsing memory map: %v", err)
	}

	// Insert the iBFT now, since nothing else has been allocated and this
	// is the most restricted allocation we're gonna have to make.
	if ibft != nil {
		ibuf := ibft.Marshal()

		// The iBFT may sit between 512K and 1M in physical memory. The
		// loaded OS finds it by scanning this region.
		allowedRange := kexec.Range{
			Start: 0x80000,
			Size:  0x80000,
		}
		r, err := m.mem.ReservePhys(uint(len(ibuf)), allowedRange)
		if err != nil {
			return fmt.Errorf("reserving space for the iBFT in %s failed: %v", allowedRange, err)
		}
		log.Printf("iBFT was allocated at %s: %#v", r, ibft)
		m.mem.Segments.Insert(kexec.NewSegment(ibuf, r))
	}

	log.Printf("Preparing multiboot info")
	if m.infoAddr, err = m.addInfo(); err != nil {
		return fmt.Errorf("error preparing multiboot info: %v", err)
	}

	log.Printf("Adding trampoline")
	if m.entryPoint, err = m.addTrampoline(); err != nil {
		return fmt.Errorf("error adding trampoline: %v", err)
	}
	log.Printf("Trampoline entry point at %#x", m.entryPoint)

	if debug {
		info, err := m.description()
		if err != nil {
			log.Printf("%v cannot create debug info: %v", DebugPrefix, err)
		}
		log.Printf("%v %v", DebugPrefix, info)
	}

	return nil
}

func getEntryPoint(r io.ReaderAt) (uintptr, error) {
	f, err := elf.NewFile(r)
	if err != nil {
		return 0, err
	}
	return uintptr(f.Entry), err
}

func (m *multiboot) addInfo() (addr uintptr, err error) {
	iw, err := m.newMultibootInfo()
	if err != nil {
		return 0, err
	}
	infoSize, err := iw.size()
	if err != nil {
		return 0, err
	}

	r, err := m.mem.FindSpace(infoSize)
	if err != nil {
		return 0, err
	}

	d, err := iw.marshal(r.Start)
	if err != nil {
		return 0, err
	}
	m.info = iw.info

	m.mem.Segments.Insert(kexec.NewSegment(d, r))
	return r.Start, nil
}

func (m multiboot) memoryMap() memoryMaps {
	var ret memoryMaps
	for _, r := range m.mem.Phys {
		typ, ok := rangeTypes[r.Type]
		if !ok {
			typ = rangeTypes[kexec.RangeDefault]
		}
		v := MemoryMap{
			// Size is really used for skipping to the next pair.
			Size:     uint32(sizeofMemoryMap) - 4,
			BaseAddr: uint64(r.Start),
			Length:   uint64(r.Size),
			Type:     typ,
		}
		ret = append(ret, v)
	}
	return ret
}

func (m *multiboot) addMmap() (addr uintptr, size uint, err error) {
	mmap := m.memoryMap()
	log.Printf("Memory map:\n%s", mmap)
	d, err := mmap.marshal()
	if err != nil {
		return 0, 0, err
	}
	r, err := m.mem.AddKexecSegment(d)
	if err != nil {
		return 0, 0, err
	}
	return r.Start, uint(len(mmap)) * sizeofMemoryMap, nil
}

func (m multiboot) memoryBoundaries() (lower, upper uint32) {
	const M1 = 1048576
	const K640 = 640 * 1024
	for _, r := range m.mem.Phys {
		if r.Type != kexec.RangeRAM {
			continue
		}
		end := uint32(r.Start) + uint32(r.Size)
		// Lower memory starts at address 0, and upper memory starts at address 1 megabyte.
		// The maximum possible value for lower memory is 640 kilobytes.
		// The value returned for upper memory is maximally the address of the first upper memory hole minus 1 megabyte.
		// It is not guaranteed to be this value.
		if r.Start <= K640 && end > lower {
			lower = end
		}
		if r.Start <= M1 && end > upper+M1 {
			upper = end - M1
		}
	}
	return
}

func min(a, b uint32) uint32 {
	if a < b {
		return a
	}
	return b
}

func (m *multiboot) newMultibootInfo() (*infoWrapper, error) {
	mmapAddr, mmapSize, err := m.addMmap()
	if err != nil {
		return nil, err
	}
	var inf info
	if m.header.Flags&flagHeaderMemoryInfo != 0 {
		lower, upper := m.memoryBoundaries()
		inf = info{
			Flags:      flagInfoMemMap | flagInfoMemory,
			MemLower:   min(uint32(lower>>10), 0xFFFFFFFF),
			MemUpper:   min(uint32(upper>>10), 0xFFFFFFFF),
			MmapLength: uint32(mmapSize),
			MmapAddr:   uint32(mmapAddr),
		}
	}

	if len(m.modules) > 0 {
		modAddr, err := m.addModules()
		if err != nil {
			return nil, err
		}
		inf.Flags |= flagInfoMods
		inf.ModsAddr = uint32(modAddr)
		inf.ModsCount = uint32(len(m.modules))
	}

	inf.CmdLine = sizeofInfo
	inf.BootLoaderName = sizeofInfo + uint32(len(m.cmdLine)) + 1
	inf.Flags |= flagInfoCmdLine | flagInfoBootLoaderName
	return &infoWrapper{
		info:           inf,
		CmdLine:        m.cmdLine,
		BootLoaderName: m.bootloader,
	}, nil
}

// marshal writes out the exact bytes expected by the multiboot info header
// specified in
// https://www.gnu.org/software/grub/manual/multiboot/multiboot.html#Boot-information-format.
func (m memoryMaps) marshal() ([]byte, error) {
	buf := bytes.Buffer{}
	err := binary.Write(&buf, ubinary.NativeEndian, m)
	return buf.Bytes(), err
}

func (m *multiboot) addTrampoline() (entry uintptr, err error) {
	// Trampoline setups the machine registers to desired state
	// and executes the loaded kernel.
	d, err := trampoline.Setup(m.trampoline, m.infoAddr, m.kernelEntry)
	if err != nil {
		return 0, err
	}

	r, err := m.mem.AddKexecSegment(d)
	if err != nil {
		return 0, err
	}
	return r.Start, nil
}