From 5a9a3b3418ab920a30ef09fdd8836ca90ab99e1e Mon Sep 17 00:00:00 2001
From: "Miouyouyou (Myy)" <myy@miouyouyou.fr>
Date: Tue, 9 Oct 2018 22:01:07 +0200
Subject: [PATCH] block: partitions: efi: Ignore bizarre Chromebook GPT
 partitions

This patch is based on @SolidHal work here :
https://raw.githubusercontent.com/SolidHal/PrawnOS/master/resources/BuildResources/patches-tested/kernel/0001-block-partitions-efi-Add-support-for-IGNOREME-GPT-si.patch

Here's the initial commit message :

8<---

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.

Borrowed from the chrome os 3.14 kernel, the commit can be found here:
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/abba28d0a1b7361da6e2023352e92687166ca30d

Also bundled in this commit
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/bd0c62c7de0c8a63314b7955e5718d8f6192f9d2%5E%21/#F0
Which is a small compiler warning fix for the above patch

This patch fixes how the kernel detects and handles certain mmc
manufatures devices, and allows the partitions on the mmc to be bootable
and mountable.

>8---

Signed-off-by: Miouyouyou (Myy) <myy@miouyouyou.fr>
---
 block/partitions/efi.c | 33 +++++++++++++++++++++++----------
 block/partitions/efi.h |  3 ++-
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/block/partitions/efi.c b/block/partitions/efi.c
index 7ca5c4c374d4..54531e49c6ab 100644
--- a/block/partitions/efi.c
+++ b/block/partitions/efi.c
@@ -328,23 +328,34 @@ 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",
+						(unsigned long long)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),
@@ -581,7 +592,7 @@ 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;
@@ -613,13 +624,13 @@ 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);
 
 	if (!good_agpt && force_gpt && fops->alternative_gpt_sector) {
 		sector_t agpt_sector;
@@ -628,14 +639,15 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
 		err = fops->alternative_gpt_sector(disk, &agpt_sector);
 		if (!err)
 			good_agpt = is_gpt_valid(state, agpt_sector,
-						 &agpt, &aptes);
+						 &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) {
@@ -652,7 +664,8 @@ 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 8cc2b88d0aa8..fcf65ebbaa85 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
 
