From 2b4a8bfd9379fd9431d517e4db20c57468ecf3e6 Mon Sep 17 00:00:00 2001
From: Julius Werner <jwerner@chromium.org>
Date: Wed, 20 Apr 2016 15:20:00 -0700
Subject: [PATCH] CHROMIUM: block: partitions: efi: Add support for IGNOREME
 GPT signature

This patch adds support for a special GPT header signature marker (using
the string 'IGNOREME' instead of the spec's 'EFI PART'). This tells the
kernel to ignore this GPT completely and look at the other one instead.
Since the kernel always prefers the primary GPT anyway, all we really
need to do effectively is to check whether the primary GPT is marked
'IGNOREME' and force evaluation of the secondary one in that case.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/340080
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>

An earlier attempt to upstream an alternative solution:
https://patchwork.kernel.org/patch/8933841/

mka@: added missing param 'lba' to log message and resolved minor
conflicts.

BUG=chromium:941638, chrome-os-partner:52595
TEST=Booted on Minnie with 'IGNOREME' primary GPT

Change-Id: Ibaee639fac9fa2f04b8836ef153c95b7d0b045a4
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1531701
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
---
 block/partitions/efi.c | 31 ++++++++++++++++++++++---------
 block/partitions/efi.h |  3 ++-
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/block/partitions/efi.c b/block/partitions/efi.c
index db2fef7dfc47..90103e0471c4 100644
--- a/block/partitions/efi.c
+++ b/block/partitions/efi.c
@@ -330,23 +330,33 @@ static gpt_header *alloc_read_gpt_header(struct parsed_partitions *state,
  * @lba: logical block address of the GPT header to test
  * @gpt: GPT header ptr, filled on return.
  * @ptes: PTEs ptr, filled on return.
+ * @ignored is filled on return with 1 if this is an IGNOREME GPT,
+ *     0 otherwise. May be NULL.
  *
  * Description: returns 1 if valid,  0 on error.
  * If valid, returns pointers to newly allocated GPT header and PTEs.
  */
 static int is_gpt_valid(struct parsed_partitions *state, u64 lba,
-			gpt_header **gpt, gpt_entry **ptes)
+			gpt_header **gpt, gpt_entry **ptes, int *ignored)
 {
 	u32 crc, origcrc;
 	u64 lastlba, pt_size;
 
+	if (ignored)
+		*ignored = 0;
 	if (!ptes)
 		return 0;
 	if (!(*gpt = alloc_read_gpt_header(state, lba)))
 		return 0;
 
 	/* Check the GUID Partition Table signature */
-	if (le64_to_cpu((*gpt)->signature) != GPT_HEADER_SIGNATURE) {
+	if (le64_to_cpu((*gpt)->signature) == GPT_HEADER_SIGNATURE_IGNORED) {
+		pr_debug("GUID Partition Table at LBA %llu marked IGNOREME\n",
+			 lba);
+		if (ignored)
+			*ignored = 1;
+		goto fail;
+	} else if (le64_to_cpu((*gpt)->signature) != GPT_HEADER_SIGNATURE) {
 		pr_debug("GUID Partition Table Header signature is wrong:"
 			 "%lld != %lld\n",
 			 (unsigned long long)le64_to_cpu((*gpt)->signature),
@@ -583,7 +593,7 @@ compare_gpts(gpt_header *pgpt, gpt_header *agpt, u64 lastlba)
 static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
 			  gpt_entry **ptes)
 {
-	int good_pgpt = 0, good_agpt = 0, good_pmbr = 0;
+	int good_pgpt = 0, good_agpt = 0, good_pmbr = 0, pgpt_ignored = 0;
 	gpt_header *pgpt = NULL, *agpt = NULL;
 	gpt_entry *pptes = NULL, *aptes = NULL;
 	legacy_mbr *legacymbr;
@@ -613,19 +623,21 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
 	}
 
 	good_pgpt = is_gpt_valid(state, GPT_PRIMARY_PARTITION_TABLE_LBA,
-				 &pgpt, &pptes);
+				 &pgpt, &pptes, &pgpt_ignored);
         if (good_pgpt)
 		good_agpt = is_gpt_valid(state,
 					 le64_to_cpu(pgpt->alternate_lba),
-					 &agpt, &aptes);
-        if (!good_agpt && force_gpt)
-                good_agpt = is_gpt_valid(state, lastlba, &agpt, &aptes);
+					 &agpt, &aptes, NULL);
+
+	if (!good_agpt && (force_gpt || pgpt_ignored))
+		good_agpt = is_gpt_valid(state, lastlba, &agpt, &aptes, NULL);
 
         /* The obviously unsuccessful case */
         if (!good_pgpt && !good_agpt)
                 goto fail;
 
-        compare_gpts(pgpt, agpt, lastlba);
+	if (!pgpt_ignored)
+		compare_gpts(pgpt, agpt, lastlba);
 
         /* The good cases */
         if (good_pgpt) {
@@ -642,7 +654,8 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
                 *ptes = aptes;
                 kfree(pgpt);
                 kfree(pptes);
-		pr_warn("Primary GPT is invalid, using alternate GPT.\n");
+		pr_warn("Primary GPT is %s, using alternate GPT.\n",
+			pgpt_ignored ? "being ignored" : "invalid");
                 return 1;
         }
 
diff --git a/block/partitions/efi.h b/block/partitions/efi.h
index 3e8576157575..260c24c54750 100644
--- a/block/partitions/efi.h
+++ b/block/partitions/efi.h
@@ -27,7 +27,8 @@
 #define GPT_MBR_PROTECTIVE  1
 #define GPT_MBR_HYBRID      2
 
-#define GPT_HEADER_SIGNATURE 0x5452415020494645ULL
+#define GPT_HEADER_SIGNATURE		0x5452415020494645ULL	/* 'EFI PART' */
+#define GPT_HEADER_SIGNATURE_IGNORED	0x454d45524f4e4749ULL	/* 'IGNOREME' */
 #define GPT_HEADER_REVISION_V1 0x00010000
 #define GPT_PRIMARY_PARTITION_TABLE_LBA 1
 
-- 
2.25.0

