cgptlib: Add support for IGNOREME GPT signature

This patch makes cgpt aware of a special "IGNOREME" GPT header signature
string that may appear in either the primary or the secondary GPT and
cause cgpt (and other cgptlib clients) to completely ignore that GPT. It
will continue to function correctly for all other purposes (using the
data from the non-ignored GPT), but never write any data back to the
ignored GPT.

BRANCH=None
BUG=chrome-os-partner:52595
TEST=unit tests

Change-Id: I7e53542385ae9d8d24dc25b75e91f4ff4917f66f
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/340072
Reviewed-by: Nam Nguyen <namnguyen@google.com>

1 files changed, 34 insertions, 32 deletions

diff --git a/firmware/lib/gpt_misc.c b/firmware/lib/gpt_misc.c
index cff9221f..0bf09401 100644
--- a/firmware/lib/gpt_misc.c
+++ b/firmware/lib/gpt_misc.c
@@ -28,6 +28,8 @@ int AllocAndReadGptData(VbExDiskHandle_t disk_handle, GptData *gptdata)
 
 	/* No data to be written yet */
 	gptdata->modified = 0;
+	/* This should get overwritten by GptInit() */
+	gptdata->ignored = 0;
 
 	/* Allocate all buffers */
 	gptdata->primary_header = (uint8_t *)VbExMalloc(gptdata->sector_bytes);
@@ -67,7 +69,11 @@ int AllocAndReadGptData(VbExDiskHandle_t disk_handle, GptData *gptdata)
 			primary_valid = 0;
 		}
 	} else {
-		VBDEBUG(("Primary GPT header invalid!\n"));
+		VBDEBUG(("Primary GPT header is %s\n",
+			 Memcmp(primary_header->signature,
+				GPT_HEADER_SIGNATURE_IGNORED,
+				GPT_HEADER_SIGNATURE_SIZE)
+			 ? "invalid" : "being ignored"));
 	}
 
 	/* Read secondary header from the end of the drive */
@@ -96,7 +102,11 @@ int AllocAndReadGptData(VbExDiskHandle_t disk_handle, GptData *gptdata)
 			secondary_valid = 0;
 		}
 	} else {
-		VBDEBUG(("Secondary GPT header invalid!\n"));
+		VBDEBUG(("Secondary GPT header is %s\n",
+			 Memcmp(secondary_header->signature,
+				GPT_HEADER_SIGNATURE_IGNORED,
+				GPT_HEADER_SIGNATURE_SIZE)
+			 ? "invalid" : "being ignored"));
 	}
 
 	/* Return 0 if least one GPT header was valid */
@@ -110,7 +120,7 @@ int AllocAndReadGptData(VbExDiskHandle_t disk_handle, GptData *gptdata)
  */
 int WriteAndFreeGptData(VbExDiskHandle_t disk_handle, GptData *gptdata)
 {
-	int legacy = 0;
+	int skip_primary = 0;
 	GptHeader *header = (GptHeader *)gptdata->primary_header;
 	uint64_t entries_bytes = header->number_of_entries
 				* header->size_of_entry;
@@ -126,19 +136,16 @@ int WriteAndFreeGptData(VbExDiskHandle_t disk_handle, GptData *gptdata)
 		GptHeader *h = (GptHeader *)(gptdata->primary_header);
 		entries_lba = h->entries_lba;
 
-		/*
-		 * Avoid even looking at this data if we don't need to. We
-		 * may in fact not have read it from disk if the read failed,
-		 * and this avoids a valgrind complaint.
-		 */
-		if (gptdata->modified) {
-			legacy = !Memcmp(h->signature, GPT_HEADER_SIGNATURE2,
-					GPT_HEADER_SIGNATURE_SIZE);
-		}
-		if (gptdata->modified & GPT_MODIFIED_HEADER1) {
-			if (legacy) {
-				VBDEBUG(("Not updating GPT header 1: "
+		if (gptdata->ignored & MASK_PRIMARY) {
+			VBDEBUG(("Not updating primary GPT: "
+				 "marked to be ignored.\n"));
+			skip_primary = 1;
+		} else if (gptdata->modified & GPT_MODIFIED_HEADER1) {
+			if (!Memcmp(h->signature, GPT_HEADER_SIGNATURE2,
+				    GPT_HEADER_SIGNATURE_SIZE)) {
+				VBDEBUG(("Not updating primary GPT: "
 					 "legacy mode is enabled.\n"));
+				skip_primary = 1;
 			} else {
 				VBDEBUG(("Updating GPT header 1\n"));
 				if (0 != VbExDiskWrite(disk_handle, 1, 1,
@@ -148,28 +155,23 @@ int WriteAndFreeGptData(VbExDiskHandle_t disk_handle, GptData *gptdata)
 		}
 	}
 
-	if (gptdata->primary_entries) {
+	if (gptdata->primary_entries && !skip_primary) {
 		if (gptdata->modified & GPT_MODIFIED_ENTRIES1) {
-			if (legacy) {
-				VBDEBUG(("Not updating GPT entries 1: "
-					 "legacy mode is enabled.\n"));
-			} else {
-				VBDEBUG(("Updating GPT entries 1\n"));
-				if (0 != VbExDiskWrite(disk_handle, entries_lba,
-						entries_sectors,
-						gptdata->primary_entries))
-					goto fail;
-			}
+			VBDEBUG(("Updating GPT entries 1\n"));
+			if (0 != VbExDiskWrite(disk_handle, entries_lba,
+					       entries_sectors,
+					       gptdata->primary_entries))
+				goto fail;
 		}
 	}
 
 	entries_lba = (gptdata->gpt_drive_sectors - entries_sectors -
 		GPT_HEADER_SECTORS);
-	if (gptdata->secondary_header) {
+	if (gptdata->secondary_header && !(gptdata->ignored & MASK_SECONDARY)) {
 		GptHeader *h = (GptHeader *)(gptdata->secondary_header);
 		entries_lba = h->entries_lba;
 		if (gptdata->modified & GPT_MODIFIED_HEADER2) {
-			VBDEBUG(("Updating GPT entries 2\n"));
+			VBDEBUG(("Updating GPT header 2\n"));
 			if (0 != VbExDiskWrite(disk_handle,
 					       gptdata->gpt_drive_sectors - 1, 1,
 					       gptdata->secondary_header))
@@ -177,12 +179,12 @@ int WriteAndFreeGptData(VbExDiskHandle_t disk_handle, GptData *gptdata)
 		}
 	}
 
-	if (gptdata->secondary_entries) {
+	if (gptdata->secondary_entries && !(gptdata->ignored & MASK_SECONDARY)){
 		if (gptdata->modified & GPT_MODIFIED_ENTRIES2) {
-			VBDEBUG(("Updating GPT header 2\n"));
+			VBDEBUG(("Updating GPT entries 2\n"));
 			if (0 != VbExDiskWrite(disk_handle,
-				entries_lba, entries_sectors,
-				gptdata->secondary_entries))
+					       entries_lba, entries_sectors,
+					       gptdata->secondary_entries))
 				goto fail;
 		}
 	}