Add --no-rs-codes flag to optionally disable reed-solomon codes in grub-install and grub-bios-setup for x86 BIOS targets.

ChangeLog

@@ -1,3 +1,8 @@
+2013-12-09  Jon McCune <jonmccune@google.com>
+
+	* Add --no-rs-codes flag to optionally disable reed-solomon codes
+	in grub-install and grub-bios-setup for x86 BIOS targets.
+
 2013-12-09  Vladimir Serbinenko  <phcoder@gmail.com>
 
 	Implement sparc64 trampolines (needed for sparc64-emu).

docs/grub.texi

@@ -5994,8 +5994,20 @@ mounted on
 Recheck the device map, even if @file{/boot/grub/device.map} already
 exists. You should use this option whenever you add/remove a disk
 into/from your computer.
-@end table
 
+@item --no-rs-codes
+By default on x86 BIOS systems, @command{grub-install} will use some
+extra space in the bootloader embedding area for Reed-Solomon
+error-correcting codes. This enables GRUB to still boot successfully
+if some blocks are corrupted.  The exact amount of protection offered
+is dependent on available space in the embedding area.  R sectors of
+redundancy can tolerate up to R/2 corrupted sectors. This
+redundancy may be cumbersome if attempting to cryptographically
+validate the contents of the bootloader embedding area, or in more
+modern systems with GPT-style partition tables (@pxref{BIOS
+installation}) where GRUB does not reside in any unpartitioned space
+outside of the MBR.  Disable the Reed-Solomon codes with this option.
+@end table
 
 @node Invoking grub-mkconfig
 @chapter Invoking grub-mkconfig

include/grub/util/install.h

@@ -183,12 +183,14 @@ void
 grub_util_bios_setup (const char *dir,
 		      const char *boot_file, const char *core_file,
 		      const char *dest, int force,
-		      int fs_probe, int allow_floppy);
+		      int fs_probe, int allow_floppy,
+		      int add_rs_codes);
 void
 grub_util_sparc_setup (const char *dir,
 		       const char *boot_file, const char *core_file,
 		       const char *dest, int force,
-		       int fs_probe, int allow_floppy);
+		       int fs_probe, int allow_floppy,
+		       int add_rs_codes);
 
 char *
 grub_install_get_image_targets_string (void);

util/grub-install.c

@@ -68,6 +68,7 @@ static int have_load_cfg = 0;
 static FILE * load_cfg_f = NULL;
 static char *load_cfg;
 static int install_bootsector = 1;
+static int add_rs_codes = 1;
 
 enum
   {
@@ -93,7 +94,8 @@ enum
     OPTION_DEBUG_IMAGE,
     OPTION_NO_FLOPPY,
     OPTION_DISK_MODULE,
-    OPTION_NO_BOOTSECTOR
+    OPTION_NO_BOOTSECTOR,
+    OPTION_NO_RS_CODES,
   };
 
 static int fs_probe = 1;
@@ -180,6 +182,10 @@ argp_parser (int key, char *arg, struct argp_state *state)
       install_bootsector = 0;
       return 0;
 
+    case OPTION_NO_RS_CODES:
+      add_rs_codes = 0;
+      return 0;
+
     case OPTION_DEBUG:
       verbosity++;
       return 0;
@@ -238,6 +244,9 @@ static struct argp_option options[] = {
    N_("do not probe for filesystems in DEVICE"), 0},
   {"no-bootsector", OPTION_NO_BOOTSECTOR, 0, 0,
    N_("do not install bootsector"), 0},
+  {"no-rs-codes", OPTION_NO_RS_CODES, 0, 0,
+   N_("Do not apply any reed-solomon codes when embedding core.img. "
+      "This option is only available on x86 BIOS targets."), 0},
 
   {"debug", OPTION_DEBUG, 0, OPTION_HIDDEN, 0, 2},
   {"no-floppy", OPTION_NO_FLOPPY, 0, OPTION_HIDDEN, 0, 2},
@@ -1435,12 +1444,13 @@ main (int argc, char *argv[])
 					      "boot.img");
 	grub_install_copy_file (boot_img_src, boot_img, 1);
 
-	grub_util_info ("%sgrub-bios-setup %s %s %s %s --directory='%s' --device-map='%s' '%s'",
+	grub_util_info ("%sgrub-bios-setup %s %s %s %s %s --directory='%s' --device-map='%s' '%s'",
 			install_bootsector ? "" : "NOT RUNNING: ",
 			allow_floppy ? "--allow-floppy " : "",
 			verbosity ? "--verbose " : "",
 			force ? "--force " : "",
 			!fs_probe ? "--skip-fs-probe" : "",
+			!add_rs_codes ? "--no-rs-codes" : "",
 			platdir,
 			device_map,
 			install_device);
@@ -1449,7 +1459,7 @@ main (int argc, char *argv[])
 	if (install_bootsector)
 	  grub_util_bios_setup (platdir, "boot.img", "core.img",
 				install_drive, force,
-				fs_probe, allow_floppy);
+				fs_probe, allow_floppy, add_rs_codes);
 	break;
       }
     case GRUB_INSTALL_PLATFORM_SPARC64_IEEE1275:
@@ -1475,7 +1485,8 @@ main (int argc, char *argv[])
 	if (install_bootsector)
 	  grub_util_sparc_setup (platdir, "boot.img", "core.img",
 				 install_device, force,
-				 fs_probe, allow_floppy);
+				 fs_probe, allow_floppy,
+				 0 /* unused */ );
 	break;
       }
 

util/grub-setup.c

@@ -64,6 +64,12 @@
 #define DEFAULT_BOOT_FILE	"boot.img"
 #define DEFAULT_CORE_FILE	"core.img"
 
+/* Non-printable "keys" for arguments with no short form.
+ * See grub-core/gnulib/argp.h for details. */
+enum {
+  NO_RS_CODES_KEY = 0x100,
+};
+
 static struct argp_option options[] = {
   {"boot-image",  'b', N_("FILE"), 0,
    N_("use FILE as the boot image [default=%s]"), 0},
@@ -82,7 +88,9 @@ static struct argp_option options[] = {
    /* TRANSLATORS: The potential breakage isn't limited to floppies but it's
       likely to make the install unbootable from HDD.  */
    N_("make the drive also bootable as floppy (default for fdX devices). May break on some BIOSes."), 0},
-
+  {"no-rs-codes", NO_RS_CODES_KEY, 0,      0,
+   N_("Do not apply any reed-solomon codes when embedding core.img. "
+      "This option is only available on x86 BIOS targets."), 0},
   { 0, 0, 0, 0, 0, 0 }
 };
 
@@ -118,6 +126,7 @@ struct arguments
   int  fs_probe;
   int allow_floppy;
   char *device;
+  int add_rs_codes;
 };
 
 static error_t
@@ -173,6 +182,10 @@ argp_parser (int key, char *arg, struct argp_state *state)
         verbosity++;
         break;
 
+      case NO_RS_CODES_KEY:
+        arguments->add_rs_codes = 0;
+        break;
+
       case ARGP_KEY_ARG:
         if (state->arg_num == 0)
           arguments->device = xstrdup(arg);
@@ -233,6 +246,7 @@ main (int argc, char *argv[])
   /* Default option values. */
   memset (&arguments, 0, sizeof (struct arguments));
   arguments.fs_probe  = 1;
+  arguments.add_rs_codes = 1;
 
   /* Parse our arguments */
   if (argp_parse (&argp, argc, argv, 0, 0, &arguments) != 0)
@@ -292,7 +306,8 @@ main (int argc, char *argv[])
 		   arguments.boot_file ? : DEFAULT_BOOT_FILE,
 		   arguments.core_file ? : DEFAULT_CORE_FILE,
 		   dest_dev, arguments.force,
-		   arguments.fs_probe, arguments.allow_floppy);
+		   arguments.fs_probe, arguments.allow_floppy,
+		   arguments.add_rs_codes);
 
   /* Free resources.  */
   grub_fini_all ();

util/setup.c

@@ -248,7 +248,8 @@ void
 SETUP (const char *dir,
        const char *boot_file, const char *core_file,
        const char *dest, int force,
-       int fs_probe, int allow_floppy)
+       int fs_probe, int allow_floppy,
+       int add_rs_codes __attribute__ ((unused))) /* unused on sparc64 */
 {
   char *core_path;
   char *boot_img, *core_img, *boot_path;
@@ -486,7 +487,11 @@ SETUP (const char *dir,
 
     nsec = core_sectors;
 
+    if (add_rs_codes)
       maxsec = 2 * core_sectors;
+    else
+      maxsec = core_sectors;
+
     if (maxsec > ((0x78000 - GRUB_KERNEL_I386_PC_LINK_ADDR)
 		>> GRUB_DISK_SECTOR_BITS))
       maxsec = ((0x78000 - GRUB_KERNEL_I386_PC_LINK_ADDR)
@@ -543,15 +548,16 @@ SETUP (const char *dir,
 
     write_rootdev (root_dev, boot_img, bl.first_sector);
 
-    core_img = realloc (core_img, nsec * GRUB_DISK_SECTOR_SIZE);
+    /* Round up to the nearest sector boundary, and zero the extra memory */
+    core_img = xrealloc (core_img, nsec * GRUB_DISK_SECTOR_SIZE);
+    assert (core_img && (nsec * GRUB_DISK_SECTOR_SIZE >= core_size));
+    memset (core_img + core_size, 0, nsec * GRUB_DISK_SECTOR_SIZE - core_size);
+
     bl.first_block = (struct grub_boot_blocklist *) (core_img
 						     + GRUB_DISK_SECTOR_SIZE
 						     - sizeof (*bl.block));
 
     grub_size_t no_rs_length;
-    grub_set_unaligned32 ((core_img + GRUB_DISK_SECTOR_SIZE
-			   + GRUB_KERNEL_I386_PC_REED_SOLOMON_REDUNDANCY),
-			  grub_host_to_target32 (nsec * GRUB_DISK_SECTOR_SIZE - core_size));
     no_rs_length = grub_target_to_host16 
       (grub_get_unaligned16 (core_img
 			     + GRUB_DISK_SECTOR_SIZE
@@ -560,6 +566,12 @@ SETUP (const char *dir,
     if (no_rs_length == 0xffff)
       grub_util_error ("%s", _("core.img version mismatch"));
 
+    if (add_rs_codes)
+      {
+	grub_set_unaligned32 ((core_img + GRUB_DISK_SECTOR_SIZE
+			       + GRUB_KERNEL_I386_PC_REED_SOLOMON_REDUNDANCY),
+			      grub_host_to_target32 (nsec * GRUB_DISK_SECTOR_SIZE - core_size));
+
 	void *tmp = xmalloc (core_size);
 	grub_memcpy (tmp, core_img, core_size);
 	grub_reed_solomon_add_redundancy (core_img + no_rs_length + GRUB_DISK_SECTOR_SIZE,
@@ -568,6 +580,7 @@ SETUP (const char *dir,
 					  - core_size);
 	assert (grub_memcmp (tmp, core_img, core_size) == 0);
 	free (tmp);
+      }
 
     /* Write the core image onto the disk.  */
     for (i = 0; i < nsec; i++)