mbr: Warn if MBR gap is small and user uses advanced modules

We don't want to support small MBR gap in pair with anything but the
simplest config of biosdisk + part_msdos + simple filesystem. In this
path "simple filesystems" are all current filesystems except ZFS and
Btrfs.

Signed-off-by: Vladimir Serbinenko <phcoder@google.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/partmap/gpt.c

@@ -25,6 +25,9 @@
 #include <grub/msdos_partition.h>
 #include <grub/gpt_partition.h>
 #include <grub/i18n.h>
+#ifdef GRUB_UTIL
+#include <grub/emu/misc.h>
+#endif
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
@@ -169,7 +172,8 @@ static grub_err_t
 gpt_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
 			 unsigned int max_nsectors,
 			 grub_embed_type_t embed_type,
-			 grub_disk_addr_t **sectors)
+			 grub_disk_addr_t **sectors,
+			 int warn_short)
 {
   struct gpt_partition_map_embed_ctx ctx = {
     .start = 0,
@@ -191,6 +195,9 @@ gpt_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
 		       N_("this GPT partition label contains no BIOS Boot Partition;"
 			  " embedding won't be possible"));
 
+  if (ctx.len < GRUB_MIN_RECOMMENDED_MBR_GAP)
+    grub_util_warn ("Your BIOS Boot Partition is under 1 MiB, please increase its size.");
+
   if (ctx.len < *nsectors)
     return grub_error (GRUB_ERR_OUT_OF_RANGE,
 		       N_("your BIOS Boot Partition is too small;"

grub-core/partmap/msdos.c

@@ -236,7 +236,8 @@ static grub_err_t
 pc_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
 			unsigned int max_nsectors,
 			grub_embed_type_t embed_type,
-			grub_disk_addr_t **sectors)
+			grub_disk_addr_t **sectors,
+			int warn_short)
 {
   grub_disk_addr_t end = ~0ULL;
   struct grub_msdos_partition_mbr mbr;
@@ -390,6 +391,9 @@ pc_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
       return GRUB_ERR_NONE;
     }
 
+  if (end < GRUB_MIN_RECOMMENDED_MBR_GAP && warn_short)
+    grub_util_warn ("You have a short MBR gap and use advanced config. Please increase post-MBR gap.");
+
   if (end <= 1)
     return grub_error (GRUB_ERR_FILE_NOT_FOUND,
 		       N_("this msdos-style partition label has no "

include/grub/partition.h

@@ -51,11 +51,14 @@ struct grub_partition_map
   grub_err_t (*iterate) (struct grub_disk *disk,
 			 grub_partition_iterate_hook_t hook, void *hook_data);
 #ifdef GRUB_UTIL
+#define GRUB_MIN_RECOMMENDED_MBR_GAP	1900
+
   /* Determine sectors available for embedding.  */
   grub_err_t (*embed) (struct grub_disk *disk, unsigned int *nsectors,
 		       unsigned int max_nsectors,
 		       grub_embed_type_t embed_type,
-		       grub_disk_addr_t **sectors);
+		       grub_disk_addr_t **sectors,
+		       int warn_short);
 #endif
 };
 typedef struct grub_partition_map *grub_partition_map_t;

include/grub/util/install.h

@@ -193,13 +193,13 @@ 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 add_rs_codes);
+		      int add_rs_codes, int warn_short_mbr_gap);
 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 add_rs_codes);
+		       int add_rs_codes, int warn_short_mbr_gap);
 
 char *
 grub_install_get_image_targets_string (void);
@@ -265,4 +265,7 @@ grub_util_get_target_name (const struct grub_install_image_target_desc *t);
 extern char *grub_install_copy_buffer;
 #define GRUB_INSTALL_COPY_BUFFER_SIZE 1048576
 
+int
+grub_install_is_short_mbrgap_supported (void);
+
 #endif

util/grub-install-common.c

@@ -234,6 +234,31 @@ char *grub_install_source_directory = NULL;
 char *grub_install_locale_directory = NULL;
 char *grub_install_themes_directory = NULL;
 
+int
+grub_install_is_short_mbrgap_supported (void)
+{
+  int i, j;
+  static const char *whitelist[] =
+    {
+     "part_msdos", "biosdisk", "affs", "afs", "bfs", "archelp",
+     "cpio", "cpio_be", "newc", "odc", "ext2", "fat", "exfat",
+     "f2fs", "fshelp", "hfs", "hfsplus", "iso9660", "jfs", "minix",
+     "minix2", "minix3", "minix_be", "minix2_be", "nilfs2", "ntfs",
+     "ntfscomp", "reiserfs", "romfs", "sfs", "tar", "udf", "ufs1",
+     "ufs1_be", "ufs2", "xfs"
+    };
+
+  for (i = 0; i < modules.n_entries; i++) {
+    for (j = 0; j < ARRAY_SIZE (whitelist); j++)
+      if (strcmp(modules.entries[i], whitelist[j]) == 0)
+	break;
+    if (j == ARRAY_SIZE (whitelist))
+      return 0;
+  }
+
+  return 1;
+}
+
 void
 grub_install_push_module (const char *val)
 {

util/grub-install.c

@@ -1721,7 +1721,8 @@ main (int argc, char *argv[])
 	if (install_bootsector)
 	  grub_util_bios_setup (platdir, "boot.img", "core.img",
 				install_drive, force,
-				fs_probe, allow_floppy, add_rs_codes);
+				fs_probe, allow_floppy, add_rs_codes,
+				!grub_install_is_short_mbrgap_supported ());
 	break;
       }
     case GRUB_INSTALL_PLATFORM_SPARC64_IEEE1275:
@@ -1748,7 +1749,7 @@ main (int argc, char *argv[])
 	  grub_util_sparc_setup (platdir, "boot.img", "core.img",
 				 install_drive, force,
 				 fs_probe, allow_floppy,
-				 0 /* unused */ );
+				 0 /* unused */, 0 /* unused */ );
 	break;
       }
 

util/grub-setup.c

@@ -315,7 +315,7 @@ main (int argc, char *argv[])
 		   arguments.core_file ? : DEFAULT_CORE_FILE,
 		   dest_dev, arguments.force,
 		   arguments.fs_probe, arguments.allow_floppy,
-		   arguments.add_rs_codes);
+		   arguments.add_rs_codes, 0);
 
   /* Free resources.  */
   grub_fini_all ();

util/setup.c

@@ -254,7 +254,8 @@ SETUP (const char *dir,
        const char *boot_file, const char *core_file,
        const char *dest, int force,
        int fs_probe, int allow_floppy,
-       int add_rs_codes __attribute__ ((unused))) /* unused on sparc64 */
+       int add_rs_codes __attribute__ ((unused)), /* unused on sparc64 */
+       int warn_small)
 {
   char *core_path;
   char *boot_img, *core_img, *boot_path;
@@ -530,7 +531,7 @@ SETUP (const char *dir,
 				 GRUB_EMBED_PCBIOS, &sectors);
     else if (ctx.dest_partmap)
       err = ctx.dest_partmap->embed (dest_dev->disk, &nsec, maxsec,
-				     GRUB_EMBED_PCBIOS, &sectors);
+				     GRUB_EMBED_PCBIOS, &sectors, warn_small);
     else
       err = fs->fs_embed (dest_dev, &nsec, maxsec,
 			  GRUB_EMBED_PCBIOS, &sectors);