[PATCH firmware-utils 1/2] ptgen: add Chromium OS kernel partition support

[Brian Norris]

Chrom{ium,e} OS (shortened as "CrOS") bootloaders use a custom GPT
partition type to locate their kernel(s), with custom attributes for
noting properties around which partition(s) should be active and how
many times they've been tried as part of their A/B in-place upgrade
system.

OpenWRT doesn't use A/B updates for upgrades (instead, just shutting
things down far enough to reprogram the necessary partitions), so all we
need to do is tell the bootloader which one is the kernel partition, and
how to use it (i.e., set the "successful" and "priority" attributes).

ptgen already supports some basic GPT partition creation, so just
add support for a '-T <GPT partition type>' argument. Currently, this
only supports '-T cros_kernel', but it could be extended if there are
other GPT partition types needed.

For GPT attribute and GUID definitions, see the CrOS verified boot
sources:

https://chromium.googlesource.com/chromiumos/platform/vboot_reference/+/refs/heads/master/firmware/lib/cgptlib/include/cgptlib_internal.h
https://chromium.googlesource.com/chromiumos/platform/vboot_reference/+/refs/heads/master/firmware/include/gpt.h

Wikipedia (!!) even notes the GUIDs:
https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs

The GUID is also recognized in fdisk, and likely other utilities, but
creation/manipulation is typically done via the 'cgpt' utility, provided
as part of the Chromium vboot_reference project.

Signed-off-by: Brian Norris <computersforpeace at gmail.com>
---
 src/ptgen.c | 43 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/src/ptgen.c b/src/ptgen.c
index 69757c1fc7dc..7220dde42b92 100644
--- a/src/ptgen.c
+++ b/src/ptgen.c
@@ -70,6 +70,10 @@ typedef struct {
 	GUID_INIT( 0x21686148, 0x6449, 0x6E6F, \
 			0x74, 0x4E, 0x65, 0x65, 0x64, 0x45, 0x46, 0x49)
 
+#define GUID_PARTITION_CHROME_OS_KERNEL \
+	GUID_INIT( 0xFE3A2A5D, 0x4F32, 0x41A7, \
+			0xB7, 0x25, 0xAC, 0xCC, 0x32, 0x85, 0xA3, 0x09)
+
 #define GUID_PARTITION_LINUX_FIT_GUID \
 	GUID_INIT( 0xcae9be83, 0xb15f, 0x49cc, \
 			0x86, 0x3f, 0x08, 0x1b, 0x74, 0x4a, 0x2d, 0x93)
@@ -116,7 +120,9 @@ struct partinfo {
 	int hybrid;
 	char *name;
 	short int required;
+	bool has_guid;
 	guid_t guid;
+	uint64_t gattr;  /* GPT partition attributes */
 };
 
 /* GPT Partition table header */
@@ -256,6 +262,23 @@ static inline int guid_parse(char *buf, guid_t *guid)
 	return 0;
 }
 
+/*
+ * Map GPT partition types to partition GUIDs.
+ * NB: not all GPT partition types have an equivalent MBR type.
+ */
+static inline bool parse_gpt_parttype(const char *type, struct partinfo *part)
+{
+	if (!strcmp(type, "cros_kernel")) {
+		part->has_guid = true;
+		part->guid = GUID_PARTITION_CHROME_OS_KERNEL;
+		/* Default attributes: bootable kernel. */
+		part->gattr = (1ULL << 48) |  /* priority=1 */
+			      (1ULL << 56);  /* success=1 */
+		return true;
+	}
+	return false;
+}
+
 /* init an utf-16 string from utf-8 string */
 static inline void init_utf16(char *str, uint16_t *buf, unsigned bufsize)
 {
@@ -416,6 +439,7 @@ static int gen_gptable(uint32_t signature, guid_t guid, unsigned nr)
 			to_chs(sect - 1, pte[1].chs_end);
 			pmbr++;
 		}
+		gpte[i].attr = parts[i].gattr;
 
 		if (parts[i].name)
 			init_utf16(parts[i].name, (uint16_t *)gpte[i].name, GPT_ENTRY_NAME_SIZE / sizeof(uint16_t));
@@ -523,7 +547,9 @@ fail:
 
 static void usage(char *prog)
 {
-	fprintf(stderr, "Usage: %s [-v] [-n] [-g] -h <heads> -s <sectors> -o <outputfile> [-a 0..4] [-l <align kB>] [-G <guid>] [[-t <type>] [-r] [-N <name>] -p <size>[@<start>]...] \n", prog);
+	fprintf(stderr, "Usage: %s [-v] [-n] [-g] -h <heads> -s <sectors> -o <outputfile>\n"
+			"          [-a 0..4] [-l <align kB>] [-G <guid>]\n"
+			"          [[-t <type> | -T <GPT part type>] [-r] [-N <name>] -p <size>[@<start>]...] \n", prog);
 	exit(EXIT_FAILURE);
 }
 
@@ -559,9 +585,8 @@ int main (int argc, char **argv)
 	uint32_t signature = 0x5452574F; /* 'OWRT' */
 	guid_t guid = GUID_INIT( signature, 0x2211, 0x4433, \
 			0x55, 0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB, 0x00);
-	guid_t part_guid = GUID_PARTITION_BASIC_DATA;
 
-	while ((ch = getopt(argc, argv, "h:s:p:a:t:o:vnHN:gl:rS:G:")) != -1) {
+	while ((ch = getopt(argc, argv, "h:s:p:a:t:T:o:vnHN:gl:rS:G:")) != -1) {
 		switch (ch) {
 		case 'o':
 			filename = optarg;
@@ -594,12 +619,12 @@ int main (int argc, char **argv)
 				*(p++) = 0;
 				parts[part].start = to_kbytes(p);
 			}
-			part_guid = type_to_guid_and_name(type, &name);
+			if (!parts[part].has_guid)
+				parts[part].guid = type_to_guid_and_name(type, &name);
 			parts[part].size = to_kbytes(optarg);
 			parts[part].required = required;
 			parts[part].name = name;
 			parts[part].hybrid = hybrid;
-			parts[part].guid = part_guid;
 			fprintf(stderr, "part %ld %ld\n", parts[part].start, parts[part].size);
 			parts[part++].type = type;
 			/*
@@ -630,6 +655,14 @@ int main (int argc, char **argv)
 		case 'S':
 			signature = strtoul(optarg, NULL, 0);
 			break;
+		case 'T':
+			if (!parse_gpt_parttype(optarg, &parts[part])) {
+				fprintf(stderr,
+					"Invalid GPT partition type \"%s\"\n",
+					optarg);
+				exit(EXIT_FAILURE);
+			}
+			break;
 		case 'G':
 			if (guid_parse(optarg, &guid)) {
 				fputs("Invalid guid string\n", stderr);
-- 
2.34.1