[PATCH v3] efi: take size of partition entry from GPT header

[PATCH v3] efi: take size of partition entry from GPT header

[Eugene Korenevsky]

Use gpt_header.sizeof_partition_entry instead of sizeof(gpt_entry)
for GPT entry size.
According to UEFI 2.7 spec 5.3.1 "GPT overview":, the size of a GUID Partition
Entry element is defined in the Size Of Partition Entry field of GPT header.
The GPT with entries sized more than sizeof(gpt_entry) is not illegal.
OVMF firmware from EDK2 perfectly works with it, see edk2-tianocore source
code.

Changes since v1: refactoring (extract get_gpt_entry function),
                  fix (&ptes[i] -> pte)
Changes since v2: use le32_to_cpu, fix typo, sanity check for
                  sizeof_partition_entry

Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>
---
 block/partitions/efi.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/block/partitions/efi.c b/block/partitions/efi.c
index 39f70d968754..c8ff7860973d 100644
--- a/block/partitions/efi.c
+++ b/block/partitions/efi.c
@@ -429,8 +429,8 @@ static int is_gpt_valid(struct parsed_partitions *state, u64 lba,
 		goto fail;
 	}
 	/* Check that sizeof_partition_entry has the correct value */
-	if (le32_to_cpu((*gpt)->sizeof_partition_entry) != sizeof(gpt_entry)) {
-		pr_debug("GUID Partition Entry Size check failed.\n");
+	if (le32_to_cpu((*gpt)->sizeof_partition_entry) < sizeof(gpt_entry)) {
+		pr_debug("GUID Partition Entry Size is too small.\n");
 		goto fail;
 	}
 
@@ -670,6 +670,12 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
         return 0;
 }
 
+static gpt_entry *get_gpt_entry(gpt_header *gpt, gpt_entry *ptes, u32 index)
+{
+	return (gpt_entry *)((u8 *)ptes +
+			le32_to_cpu(gpt->sizeof_partition_entry) * index);
+}
+
 /**
  * efi_partition(struct parsed_partitions *state)
  * @state: disk parsed partitions
@@ -704,32 +710,36 @@ int efi_partition(struct parsed_partitions *state)
 
 	pr_debug("GUID Partition Table is valid!  Yea!\n");
 
-	for (i = 0; i < le32_to_cpu(gpt->num_partition_entries) && i < state->limit-1; i++) {
+	for (i = 0;
+	     i < le32_to_cpu(gpt->num_partition_entries) && i < state->limit-1;
+	     i++) {
+		gpt_entry *pte = get_gpt_entry(gpt, ptes, i);
 		struct partition_meta_info *info;
 		unsigned label_count = 0;
 		unsigned label_max;
-		u64 start = le64_to_cpu(ptes[i].starting_lba);
-		u64 size = le64_to_cpu(ptes[i].ending_lba) -
-			   le64_to_cpu(ptes[i].starting_lba) + 1ULL;
+		u64 start = le64_to_cpu(pte->starting_lba);
+		u64 size = le64_to_cpu(pte->ending_lba) -
+			   le64_to_cpu(pte->starting_lba) + 1ULL;
 
-		if (!is_pte_valid(&ptes[i], last_lba(state->bdev)))
+		if (!is_pte_valid(pte, last_lba(state->bdev)))
 			continue;
 
 		put_partition(state, i+1, start * ssz, size * ssz);
 
 		/* If this is a RAID volume, tell md */
-		if (!efi_guidcmp(ptes[i].partition_type_guid, PARTITION_LINUX_RAID_GUID))
+		if (!efi_guidcmp(
+		    pte->partition_type_guid, PARTITION_LINUX_RAID_GUID))
 			state->parts[i + 1].flags = ADDPART_FLAG_RAID;
 
 		info = &state->parts[i + 1].info;
-		efi_guid_to_str(&ptes[i].unique_partition_guid, info->uuid);
+		efi_guid_to_str(&pte->unique_partition_guid, info->uuid);
 
 		/* Naively convert UTF16-LE to 7 bits. */
 		label_max = min(ARRAY_SIZE(info->volname) - 1,
-				ARRAY_SIZE(ptes[i].partition_name));
+				ARRAY_SIZE(pte->partition_name));
 		info->volname[label_max] = 0;
 		while (label_count < label_max) {
-			u8 c = ptes[i].partition_name[label_count] & 0xff;
+			u8 c = pte->partition_name[label_count] & 0xff;
 			if (c && !isprint(c))
 				c = '!';
 			info->volname[label_count] = c;
-- 
2.18.0

Re: [PATCH v3] efi: take size of partition entry from GPT header

[Davidlohr Bueso]

On Wed, 12 Sep 2018, Eugene Korenevsky wrote:
> /**
>  * efi_partition(struct parsed_partitions *state)
>  * @state: disk parsed partitions
>@@ -704,32 +710,36 @@ int efi_partition(struct parsed_partitions *state)
>
> 	pr_debug("GUID Partition Table is valid!  Yea!\n");
>
>-	for (i = 0; i < le32_to_cpu(gpt->num_partition_entries) && i < state->limit-1; i++) {
>+	for (i = 0;
>+	     i < le32_to_cpu(gpt->num_partition_entries) && i < state->limit-1;
>+	     i++) {

Please rearrange this like:

       for (i = 0;  < le32_to_cpu(gpt->num_partition_entries) &&
       	      	      i < state->limit-1; i++)

>+		gpt_entry *pte = get_gpt_entry(gpt, ptes, i);
> 		struct partition_meta_info *info;
> 		unsigned label_count = 0;
> 		unsigned label_max;
>-		u64 start = le64_to_cpu(ptes[i].starting_lba);
>-		u64 size = le64_to_cpu(ptes[i].ending_lba) -
>-			   le64_to_cpu(ptes[i].starting_lba) + 1ULL;
>+		u64 start = le64_to_cpu(pte->starting_lba);
>+		u64 size = le64_to_cpu(pte->ending_lba) -
>+			   le64_to_cpu(pte->starting_lba) + 1ULL;
>
>-		if (!is_pte_valid(&ptes[i], last_lba(state->bdev)))
>+		if (!is_pte_valid(pte, last_lba(state->bdev)))
> 			continue;
>
> 		put_partition(state, i+1, start * ssz, size * ssz);
>
> 		/* If this is a RAID volume, tell md */
>-		if (!efi_guidcmp(ptes[i].partition_type_guid, PARTITION_LINUX_RAID_GUID))
>+		if (!efi_guidcmp(
>+		    pte->partition_type_guid, PARTITION_LINUX_RAID_GUID))

This is ugly. If you are worried about 80-chars, please do:

     	      	 if (!efi_guidcmp(pte->partition_type_guid,
				PARTITION_LINUX_RAID_GUID))

Thanks,
Davidlohr

RE: [PATCH v3] efi: take size of partition entry from GPT header

[David Laight]

From: Davidlohr Bueso
> Sent: 12 September 2018 19:55
> 
> On Wed, 12 Sep 2018, Eugene Korenevsky wrote:
> > /**
> >  * efi_partition(struct parsed_partitions *state)
> >  * @state: disk parsed partitions
> >@@ -704,32 +710,36 @@ int efi_partition(struct parsed_partitions *state)
> >
> > 	pr_debug("GUID Partition Table is valid!  Yea!\n");
> >
> >-	for (i = 0; i < le32_to_cpu(gpt->num_partition_entries) && i < state->limit-1; i++) {
> >+	for (i = 0;
> >+	     i < le32_to_cpu(gpt->num_partition_entries) && i < state->limit-1;
> >+	     i++) {
> 
> Please rearrange this like:
> 
>        for (i = 0; i < le32_to_cpu(gpt->num_partition_entries) &&
>        	      	      i < state->limit-1; i++)

Better still cache le32_to_cpu(gpt->num_partition_entries) to a local
so that it only has to be calculated once (even if it gets spilled
to the stack).
It can be bounded by state->limit-1 at the same time.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH v3] efi: take size of partition entry from GPT header

[Eugene Korenevsky]

> > Please rearrange this like:
> >
> >        for (i = 0; i < le32_to_cpu(gpt->num_partition_entries) &&
> >                             i < state->limit-1; i++)
>
> Better still cache le32_to_cpu(gpt->num_partition_entries) to a local
> so that it only has to be calculated once (even if it gets spilled
> to the stack).
> It can be bounded by state->limit-1 at the same time.

This is block I/O, slow path. No need for such micro optimizations here.
GCC is capable to do such optimizations automatically, and it does as
I can see from disassembly.
Anyway this would be a subject for another patch.

-- 
Eugene