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grub.go
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grub.go
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// Copyright 2017-2020 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 grub implements a grub config file parser.
//
// See the grub manual https://www.gnu.org/software/grub/manual/grub/ for
// a reference of the configuration format
// In particular the following pages:
// - https://www.gnu.org/software/grub/manual/grub/html_node/Shell_002dlike-scripting.html
// - https://www.gnu.org/software/grub/manual/grub/html_node/Commands.html
//
// Currently, only the linux[16|efi], initrd[16|efi], menuentry and set
// directives are partially supported.
package grub
import (
"context"
"fmt"
"io"
"log"
"net/url"
"path/filepath"
"strconv"
"strings"
"github.com/u-root/u-root/pkg/boot"
"github.com/u-root/u-root/pkg/boot/multiboot"
"github.com/u-root/u-root/pkg/curl"
"github.com/u-root/u-root/pkg/shlex"
"github.com/u-root/u-root/pkg/uio"
)
var probeGrubFiles = []string{
"boot/grub/grub.cfg",
"grub/grub.cfg",
"grub2/grub.cfg",
"boot/grub2/grub.cfg",
}
// ParseLocalConfig looks for a GRUB config in the disk partition mounted at
// diskDir and parses out OSes to boot.
//
// This... is at best crude, at worst totally wrong, since we fundamentally
// assume that the kernels we boot are only on this one partition. But so is
// this whole parser.
func ParseLocalConfig(ctx context.Context, diskDir string) ([]boot.OSImage, error) {
wd := &url.URL{
Scheme: "file",
Path: diskDir,
}
// This is a hack. GRUB should stop caring about URLs at least in the
// way we use them today, because GRUB has additional path encoding
// methods. Sorry.
//
// Normally, stuff like this will be in EFI/BOOT/grub.cfg, but some
// distro's have their own directory in this EFI namespace. Just check
// 'em all.
files, err := filepath.Glob(filepath.Join(diskDir, "EFI", "*", "grub.cfg"))
if err != nil {
log.Printf("[grub] Could not glob for %s/EFI/*/grub.cfg: %v", diskDir, err)
}
var relNames []string
for _, file := range files {
base, err := filepath.Rel(diskDir, file)
if err == nil {
relNames = append(relNames, base)
}
}
for _, relname := range append(relNames, probeGrubFiles...) {
c, err := ParseConfigFile(ctx, curl.DefaultSchemes, relname, wd)
if curl.IsURLError(err) {
continue
}
return c, err
}
return nil, fmt.Errorf("no valid grub config found")
}
// ParseConfigFile parses a grub configuration as specified in
// https://www.gnu.org/software/grub/manual/grub/
//
// Currently, only the linux[16|efi], initrd[16|efi], menuentry and set
// directives are partially supported.
//
// `wd` is the default scheme, host, and path for any files named as a
// relative path - e.g. kernel, include, and initramfs paths are requested
// relative to the wd.
func ParseConfigFile(ctx context.Context, s curl.Schemes, configFile string, wd *url.URL) ([]boot.OSImage, error) {
p := newParser(wd, s)
if err := p.appendFile(ctx, configFile); err != nil {
return nil, err
}
// Don't add entries twice.
//
// Multiple labels can refer to the same image, so we have to dedup by pointer.
seenLinux := make(map[*boot.LinuxImage]struct{})
seenMB := make(map[*boot.MultibootImage]struct{})
if len(p.defaultEntry) > 0 {
p.labelOrder = append([]string{p.defaultEntry}, p.labelOrder...)
}
var images []boot.OSImage
for _, label := range p.labelOrder {
if img, ok := p.linuxEntries[label]; ok {
if _, ok := seenLinux[img]; !ok {
images = append(images, img)
seenLinux[img] = struct{}{}
}
}
if img, ok := p.mbEntries[label]; ok {
if _, ok := seenMB[img]; !ok {
images = append(images, img)
seenMB[img] = struct{}{}
}
}
}
return images, nil
}
type parser struct {
linuxEntries map[string]*boot.LinuxImage
mbEntries map[string]*boot.MultibootImage
labelOrder []string
defaultEntry string
W io.Writer
// parser internals.
numEntry int
// curEntry is the current entry number as a string.
curEntry string
// curLabel is the last parsed label from a "menuentry".
curLabel string
wd *url.URL
schemes curl.Schemes
}
// newParser returns a new grub parser using working directory `wd`
// and schemes `s`.
//
// If a path encountered in a configuration file is relative instead of a full
// URL, `wd` is used as the "working directory" of that relative path; the
// resulting URL is roughly `wd.String()/path`.
//
// `s` is used to get files referred to by URLs.
func newParser(wd *url.URL, s curl.Schemes) *parser {
return &parser{
linuxEntries: make(map[string]*boot.LinuxImage),
mbEntries: make(map[string]*boot.MultibootImage),
wd: wd,
schemes: s,
}
}
func parseURL(surl string, wd *url.URL) (*url.URL, error) {
u, err := url.Parse(surl)
if err != nil {
return nil, fmt.Errorf("could not parse URL %q: %v", surl, err)
}
if len(u.Scheme) == 0 {
u.Scheme = wd.Scheme
if len(u.Host) == 0 {
// If this is not there, it was likely just a path.
u.Host = wd.Host
u.Path = filepath.Join(wd.Path, filepath.Clean(u.Path))
}
}
return u, nil
}
// getFile parses `url` relative to the config's working directory and returns
// an io.Reader for the requested url.
//
// If url is just a relative path and not a full URL, c.wd is used as the
// "working directory" of that relative path; the resulting URL is roughly
// path.Join(wd.String(), url).
func (c *parser) getFile(url string) (io.ReaderAt, error) {
u, err := parseURL(url, c.wd)
if err != nil {
return nil, err
}
return c.schemes.LazyFetch(u)
}
// appendFile parses the config file downloaded from `url` and adds it to `c`.
func (c *parser) appendFile(ctx context.Context, url string) error {
u, err := parseURL(url, c.wd)
if err != nil {
return err
}
r, err := c.schemes.Fetch(ctx, u)
if err != nil {
return err
}
config, err := uio.ReadAll(r)
if err != nil {
return err
}
if len(config) > 500 {
// Avoid flooding the console on real systems
// TODO: do we want to pass a verbose flag or a logger?
log.Printf("[grub] Got config file %s", r)
} else {
log.Printf("[grub] Got config file %s:\n%s\n", r, string(config))
}
return c.append(ctx, string(config))
}
// CmdlineQuote quotes the command line as grub-core/lib/cmdline.c does
func cmdlineQuote(args []string) string {
q := make([]string, len(args))
for i, s := range args {
s = strings.Replace(s, `\`, `\\`, -1)
s = strings.Replace(s, `'`, `\'`, -1)
s = strings.Replace(s, `"`, `\"`, -1)
if strings.ContainsRune(s, ' ') {
s = `"` + s + `"`
}
q[i] = s
}
return strings.Join(q, " ")
}
// append parses `config` and adds the respective configuration to `c`.
//
// NOTE: This parser has outlived its usefulness already, given that it doesn't
// even understand the {} scoping in GRUB. But let's get the tests to pass, and
// then we can do a rewrite.
func (c *parser) append(ctx context.Context, config string) error {
// Here's a shitty parser.
for _, line := range strings.Split(config, "\n") {
kv := shlex.Argv(line)
if len(kv) < 1 {
continue
}
directive := strings.ToLower(kv[0])
// Used by tests (allow no parameters here)
if c.W != nil && directive == "echo" {
fmt.Fprintf(c.W, "echo:%#v\n", kv[1:])
}
if len(kv) <= 1 {
continue
}
arg := kv[1]
switch directive {
case "set":
vals := strings.SplitN(arg, "=", 2)
if len(vals) == 2 {
//TODO handle vars? bootVars[vals[0]] = vals[1]
//log.Printf("grubvar: %s=%s", vals[0], vals[1])
if vals[0] == "default" {
c.defaultEntry = vals[1]
}
}
case "configfile":
// TODO test that
if err := c.appendFile(ctx, arg); err != nil {
return err
}
case "menuentry":
c.curEntry = strconv.Itoa(c.numEntry)
c.curLabel = arg
c.numEntry++
c.labelOrder = append(c.labelOrder, c.curEntry, c.curLabel)
case "linux", "linux16", "linuxefi":
k, err := c.getFile(arg)
if err != nil {
return err
}
// from grub manual: "Any initrd must be reloaded after using this command" so we can replace the entry
entry := &boot.LinuxImage{
Name: c.curLabel,
Kernel: k,
Cmdline: cmdlineQuote(kv[2:]),
}
c.linuxEntries[c.curEntry] = entry
c.linuxEntries[c.curLabel] = entry
case "initrd", "initrd16", "initrdefi":
if e, ok := c.linuxEntries[c.curEntry]; ok {
i, err := c.getFile(arg)
if err != nil {
return err
}
e.Initrd = i
}
case "multiboot":
// TODO handle --quirk-* arguments ? (change parsing)
k, err := c.getFile(arg)
if err != nil {
return err
}
// from grub manual: "Any initrd must be reloaded after using this command" so we can replace the entry
entry := &boot.MultibootImage{
Name: c.curLabel,
Kernel: k,
Cmdline: cmdlineQuote(kv[2:]),
}
c.mbEntries[c.curEntry] = entry
c.mbEntries[c.curLabel] = entry
case "module":
// TODO handle --nounzip arguments ? (change parsing)
if e, ok := c.mbEntries[c.curEntry]; ok {
// The only allowed arg
cmdline := kv[1:]
if arg == "--nounzip" {
arg = kv[2]
cmdline = kv[2:]
}
m, err := c.getFile(arg)
if err != nil {
return err
}
// TODO: Lasy tryGzipFilter(m)
mod := multiboot.Module{
Module: m,
Cmdline: cmdlineQuote(cmdline),
}
e.Modules = append(e.Modules, mod)
}
}
}
return nil
}