Re: [PATCH v3] partitions/efi: Fix partition name parsing in GUID partition entry

[Nikolai Merinov <n.merinov@inango-systems.com>]

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Hi Christoph, 

> I'd rather use plain __le16 and le16_to_cpu here. Also the be 
> variants seems to be entirely unused. 

Looks like I misunderstood your comment from https://patchwork.kernel.org/patch/11309223/: 

> Please add a an efi_char_from_cpu or similarly named helper 
> to encapsulate this logic. 

The "le16_to_cpu(ptes[i].partition_name[label_count])" call is the 
full implementation of the "efi_char_from_cpu" logic. Do you want 
to encapsulate "utf16_le_to_7bit_string" logic entirely like in
the attached version?

Regards,
Nikolai

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From 842cf22d6f6f91872bcb04ac6abe7794fede23fd Mon Sep 17 00:00:00 2001
From: Nikolai Merinov <n.merinov@inango-systems.com>
Date: Sat, 24 Nov 2018 20:42:27 +0500
Subject: [PATCH v4] partitions/efi: Fix partition name parsing in GUID
 partition entry

GUID partition entry defined to have a partition name as 36 UTF-16LE
code units. This means that on big-endian platforms ASCII symbols
would be read with 0xXX00 efi_char16_t character code. In order to
correctly extract ASCII characters from a partition name field we
should be converted from 16LE to CPU architecture.

The problem exists on all big endian platforms.

Signed-off-by: Nikolai Merinov <n.merinov@inango-systems.com>
Fixes: eec7ecfede74 ("genhd, efi: add efi partition metadata to hd_structs")
---
 block/partitions/efi.c | 35 ++++++++++++++++++++++++++---------
 block/partitions/efi.h |  2 +-
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/block/partitions/efi.c b/block/partitions/efi.c
index db2fef7dfc47..d26a0654d7ca 100644
--- a/block/partitions/efi.c
+++ b/block/partitions/efi.c
@@ -656,6 +656,30 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
         return 0;
 }
 
+/**
+ * utf16_le_to_7bit(): Naively converts UTF-16LE string to 7bit characters
+ * @in: input UTF-16LE string
+ * @size: size of the input string
+ * @out: output string ptr, should be capable to store @size+1 characters
+ *
+ * Description: Converts @size UTF16-LE symbols from @in string to 7bit
+ * characters and store them to @out. Adds trailing zero to @out array.
+ */
+static void utf16_le_to_7bit(const __le16 *in, unsigned int size, u8 *out)
+{
+	unsigned int i = 0;
+
+	out[size] = 0;
+	while (i < size) {
+		u8 c = le16_to_cpu(in[i]) & 0xff;
+
+		if (c && !isprint(c))
+			c = '!';
+		out[i] = c;
+		i++;
+	}
+}
+
 /**
  * efi_partition(struct parsed_partitions *state)
  * @state: disk parsed partitions
@@ -692,7 +716,6 @@ int efi_partition(struct parsed_partitions *state)
 
 	for (i = 0; i < le32_to_cpu(gpt->num_partition_entries) && i < state->limit-1; 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) -
@@ -713,14 +736,8 @@ int efi_partition(struct parsed_partitions *state)
 		/* Naively convert UTF16-LE to 7 bits. */
 		label_max = min(ARRAY_SIZE(info->volname) - 1,
 				ARRAY_SIZE(ptes[i].partition_name));
-		info->volname[label_max] = 0;
-		while (label_count < label_max) {
-			u8 c = ptes[i].partition_name[label_count] & 0xff;
-			if (c && !isprint(c))
-				c = '!';
-			info->volname[label_count] = c;
-			label_count++;
-		}
+		utf16_le_to_7bit(ptes[i].partition_name, label_max,
+				 info->volname);
 		state->parts[i + 1].has_info = true;
 	}
 	kfree(ptes);
diff --git a/block/partitions/efi.h b/block/partitions/efi.h
index 3e8576157575..0b6d5b7be111 100644
--- a/block/partitions/efi.h
+++ b/block/partitions/efi.h
@@ -88,7 +88,7 @@ typedef struct _gpt_entry {
 	__le64 starting_lba;
 	__le64 ending_lba;
 	gpt_entry_attributes attributes;
-	efi_char16_t partition_name[72 / sizeof (efi_char16_t)];
+	__le16 partition_name[72 / sizeof (__le16)];
 } __packed gpt_entry;
 
 typedef struct _gpt_mbr_record {
-- 
2.17.1