cgpt: Support non-standard (smaller) entries table

The standard says that entries table must be at least 16384 bytes. On
some of our devices, the NOR section is only 8 KiB and used to store
both primary and secondary tables. On this device, we can only store 24
entries.

Therefore, this CL adds support for non-standard entry table. It adjusts
the MIN_NUMBER_OF_ENTRIES to 16, and replaces GPT_ENTRIES_SECTORS with
CalculateEntriesSectors.

BUG=chromium:441812
BRANCH=none
TEST=unittest

Change-Id: I6b85b35ce5612c7abb22142f8252bd0d45b676c5
Reviewed-on: https://chromium-review.googlesource.com/234996
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
Commit-Queue: Nam Nguyen <namnguyen@chromium.org>
Tested-by: Nam Nguyen <namnguyen@chromium.org>

2 files changed, 22 insertions, 13 deletions

diff --git a/firmware/lib/cgptlib/cgptlib_internal.c b/firmware/lib/cgptlib/cgptlib_internal.c
index 5e2889c6..6a89d841 100644
--- a/firmware/lib/cgptlib/cgptlib_internal.c
+++ b/firmware/lib/cgptlib/cgptlib_internal.c
@@ -12,11 +12,18 @@
 #include "gpt_misc.h"
 #include "utility.h"
 
+const static int SECTOR_SIZE = 512;
+
+size_t CalculateEntriesSectors(GptHeader* h) {
+  size_t bytes = h->number_of_entries * h->size_of_entry;
+  size_t ret = (bytes + SECTOR_SIZE - 1) / SECTOR_SIZE;
+  return ret;
+}
 
 int CheckParameters(GptData *gpt)
 {
 	/* Currently, we only support 512-byte sectors. */
-	if (gpt->sector_bytes != 512)
+	if (gpt->sector_bytes != SECTOR_SIZE)
 		return GPT_ERROR_INVALID_SECTOR_SIZE;
 
 	/*
@@ -33,9 +40,11 @@ int CheckParameters(GptData *gpt)
 	/*
 	 * Sector count of a drive should be reasonable. If the given value is
 	 * too small to contain basic GPT structure (PMBR + Headers + Entries),
-	 * the value is wrong.
+	 * the value is wrong. Entries size is hard coded to TOTAL_ENTRIES_SIZE (see
+	 * cgpt_create.c). This check is only applicable when GPT is stored on device.
 	 */
-	if (gpt->gpt_drive_sectors < (1 + 2 * (1 + GPT_ENTRIES_SECTORS)))
+	if (!(gpt->flags & GPT_FLAG_EXTERNAL) &&
+		gpt->gpt_drive_sectors < (1 + 2 * (1 + TOTAL_ENTRIES_SIZE / SECTOR_SIZE)))
 		return GPT_ERROR_INVALID_SECTOR_NUMBER;
 
 	return GPT_SUCCESS;
@@ -105,7 +114,7 @@ int CheckHeader(GptHeader *h, int is_secondary,
 	if (is_secondary) {
 		if (h->my_lba != gpt_drive_sectors - GPT_HEADER_SECTORS)
 			return 1;
-		if (h->entries_lba != h->my_lba - GPT_ENTRIES_SECTORS)
+		if (h->entries_lba != h->my_lba - CalculateEntriesSectors(h))
 			return 1;
 	} else {
 		if (h->my_lba != GPT_PMBR_SECTORS)
@@ -131,10 +140,10 @@ int CheckHeader(GptHeader *h, int is_secondary,
 	 * array.
 	 */
 	/* TODO(namnguyen): Also check for padding between header & entries. */
-	if (h->first_usable_lba < 2 + GPT_ENTRIES_SECTORS)
+	if (h->first_usable_lba < 2 + CalculateEntriesSectors(h))
 		return 1;
 	if (h->last_usable_lba >=
-			streaming_drive_sectors - 1 - GPT_ENTRIES_SECTORS)
+			streaming_drive_sectors - 1 - CalculateEntriesSectors(h))
 		return 1;
 
 	/* Success */
@@ -321,7 +330,7 @@ void GptRepair(GptData *gpt)
 		Memcpy(header2, header1, sizeof(GptHeader));
 		header2->my_lba = gpt->gpt_drive_sectors - GPT_HEADER_SECTORS;
 		header2->alternate_lba = GPT_PMBR_SECTORS;  /* Second sector. */
-		header2->entries_lba = header2->my_lba - GPT_ENTRIES_SECTORS;
+		header2->entries_lba = header2->my_lba - CalculateEntriesSectors(header1);
 		header2->header_crc32 = HeaderCrc(header2);
 		gpt->modified |= GPT_MODIFIED_HEADER2;
 	}
diff --git a/firmware/lib/cgptlib/include/cgptlib_internal.h b/firmware/lib/cgptlib/include/cgptlib_internal.h
index f88bc567..b4e2f5f9 100644
--- a/firmware/lib/cgptlib/include/cgptlib_internal.h
+++ b/firmware/lib/cgptlib/include/cgptlib_internal.h
@@ -51,17 +51,12 @@
 #define MIN_SIZE_OF_ENTRY 128
 #define MAX_SIZE_OF_ENTRY 512
 #define SIZE_OF_ENTRY_MULTIPLE 8
-#define MIN_NUMBER_OF_ENTRIES 32
+#define MIN_NUMBER_OF_ENTRIES 16
 #define MAX_NUMBER_OF_ENTRIES 512
 
 /* Defines GPT sizes */
 #define GPT_PMBR_SECTORS 1  /* size (in sectors) of PMBR */
 #define GPT_HEADER_SECTORS 1
-/*
- * Entries sectors assumes sector size if 512 bytes; then (TOTAL_ENTRIES_SIZE /
- * 512) = 32
- */
-#define GPT_ENTRIES_SECTORS 32
 
 /*
  * Alias name of index in internal array for primary and secondary header and
@@ -163,4 +158,9 @@ void GetCurrentKernelUniqueGuid(GptData *gpt, void *dest);
  */
 const char *GptErrorText(int error_code);
 
+/**
+ * Return number of 512-byte sectors required to store the entries table.
+ */
+size_t CalculateEntriesSectors(GptHeader* h);
+
 #endif /* VBOOT_REFERENCE_CGPTLIB_INTERNAL_H_ */