partitions/efi: account for pmbr size in lba

The partition that has the 0xEE (GPT protective), must have the size in
lba field set to the lesser of the size of the disk minus one or
0xFFFFFFFF for larger disks.
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Reviewed-by: Karel Zak <kzak@redhat.com>
Acked-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

block/partitions/efi.c

@@ -166,6 +166,7 @@ static inline int pmbr_part_valid(gpt_mbr_record *part)
 /**
  * is_pmbr_valid(): test Protective MBR for validity
  * @mbr: pointer to a legacy mbr structure
+ * @total_sectors: amount of sectors in the device
  *
  * Description: Checks for a valid protective or hybrid
  * master boot record (MBR). The validity of a pMBR depends
@@ -180,9 +181,9 @@ static inline int pmbr_part_valid(gpt_mbr_record *part)
  * Returns 0 upon invalid MBR, or GPT_MBR_PROTECTIVE or
  * GPT_MBR_HYBRID depending on the device layout.
  */
-static int is_pmbr_valid(legacy_mbr *mbr)
+static int is_pmbr_valid(legacy_mbr *mbr, sector_t total_sectors)
 {
-	int i, ret = 0; /* invalid by default */
+	int i, part = 0, ret = 0; /* invalid by default */
 
 	if (!mbr || le16_to_cpu(mbr->signature) != MSDOS_MBR_SIGNATURE)
 		goto done;
@@ -190,6 +191,7 @@ static int is_pmbr_valid(legacy_mbr *mbr)
 	for (i = 0; i < 4; i++) {
 		ret = pmbr_part_valid(&mbr->partition_record[i]);
 		if (ret == GPT_MBR_PROTECTIVE) {
+			part = i;
 			/*
 			 * Ok, we at least know that there's a protective MBR,
 			 * now check if there are other partition types for
@@ -207,6 +209,18 @@ static int is_pmbr_valid(legacy_mbr *mbr)
 			EFI_PMBR_OSTYPE_EFI_GPT) &&
 		    (mbr->partition_record[i].os_type != 0x00))
 			ret = GPT_MBR_HYBRID;
+
+	/*
+	 * Protective MBRs take up the lesser of the whole disk
+	 * or 2 TiB (32bit LBA), ignoring the rest of the disk.
+	 *
+	 * Hybrid MBRs do not necessarily comply with this.
+	 */
+	if (ret == GPT_MBR_PROTECTIVE) {
+		if (le32_to_cpu(mbr->partition_record[part].size_in_lba) !=
+		    min((uint32_t) total_sectors - 1, 0xFFFFFFFF))
+			ret = 0;
+	}
 done:
 	return ret;
 }
@@ -568,6 +582,7 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
 	gpt_header *pgpt = NULL, *agpt = NULL;
 	gpt_entry *pptes = NULL, *aptes = NULL;
 	legacy_mbr *legacymbr;
+	sector_t total_sectors = i_size_read(state->bdev->bd_inode) >> 9;
 	u64 lastlba;
 
 	if (!ptes)
@@ -581,7 +596,7 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
 			goto fail;
 
 		read_lba(state, 0, (u8 *)legacymbr, sizeof(*legacymbr));
-		good_pmbr = is_pmbr_valid(legacymbr);
+		good_pmbr = is_pmbr_valid(legacymbr, total_sectors);
 		kfree(legacymbr);
 
 		if (!good_pmbr)