linux-kernel - [PATCH 1/2] efi: Add a generic helper to convert strings to unicode

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Date:   Fri, 20 May 2022 16:50:27 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     ardb@...nel.org, linux-efi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-dev@...lia.com,
        kernel@...ccoli.net, anton@...msg.org, ccross@...roid.com,
        keescook@...omium.org, matt@...eblueprint.co.uk,
        matthew.garrett@...ula.com, tony.luck@...el.com,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Subject: [PATCH 1/2] efi: Add a generic helper to convert strings to unicode

Currently both efi-pstore and efibc rely in simple for-loops
to convert from regular char pointers to u16/unicode strings;
efibc has even a nice helper to perform such work.

So, let's export this helper to common EFI code to prevent
code duplication (like in efi-pstore); this helper will also
be used in a subsequent patch (adding a new module).

Notice that efi-pstore didn't write the end NULL char in the
unicode string before this patch, but this should not change
anything. No functional change is expected here.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
---
 drivers/firmware/efi/efi-pstore.c |  5 ++---
 drivers/firmware/efi/efibc.c      | 16 ++++------------
 include/linux/efi.h               | 15 +++++++++++++++
 3 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index 7e771c56c13c..299116ecfb4e 100644
--- a/drivers/firmware/efi/efi-pstore.c
+++ b/drivers/firmware/efi/efi-pstore.c
@@ -249,7 +249,7 @@ static int efi_pstore_write(struct pstore_record *record)
 	char name[DUMP_NAME_LEN];
 	efi_char16_t efi_name[DUMP_NAME_LEN];
 	efi_guid_t vendor = LINUX_EFI_CRASH_GUID;
-	int i, ret = 0;
+	int ret = 0;
 
 	record->id = generic_id(record->time.tv_sec, record->part,
 				record->count);
@@ -262,8 +262,7 @@ static int efi_pstore_write(struct pstore_record *record)
 		 (long long)record->time.tv_sec,
 		 record->compressed ? 'C' : 'D');
 
-	for (i = 0; i < DUMP_NAME_LEN; i++)
-		efi_name[i] = name[i];
+	efi_str8_to_str16(efi_name, name, DUMP_NAME_LEN - 1);
 
 	ret = efivar_entry_set_safe(efi_name, vendor, PSTORE_EFI_ATTRIBUTES,
 			      false, record->size, record->psi->buf);
diff --git a/drivers/firmware/efi/efibc.c b/drivers/firmware/efi/efibc.c
index 15a47539dc56..63fe2bf753cb 100644
--- a/drivers/firmware/efi/efibc.c
+++ b/drivers/firmware/efi/efibc.c
@@ -11,16 +11,6 @@
 #include <linux/reboot.h>
 #include <linux/slab.h>
 
-static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
-{
-	size_t i;
-
-	for (i = 0; i < strlen(str); i++)
-		str16[i] = str[i];
-
-	str16[i] = '\0';
-}
-
 static int efibc_set_variable(const char *name, const char *value)
 {
 	int ret;
@@ -39,8 +29,10 @@ static int efibc_set_variable(const char *name, const char *value)
 		return -ENOMEM;
 	}
 
-	efibc_str_to_str16(name, entry->var.VariableName);
-	efibc_str_to_str16(value, (efi_char16_t *)entry->var.Data);
+	efi_str8_to_str16(entry->var.VariableName, name, strlen(name));
+	efi_str8_to_str16((efi_char16_t *)entry->var.Data, value,
+			  strlen(value));
+
 	memcpy(&entry->var.VendorGuid, &guid, sizeof(guid));
 
 	ret = efivar_entry_set_safe(entry->var.VariableName,
diff --git a/include/linux/efi.h b/include/linux/efi.h
index ccd4d3f91c98..066ebc5bcb2a 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1030,6 +1030,21 @@ efivar_unregister(struct efivar_entry *var)
 	kobject_put(&var->kobj);
 }
 
+/*
+ * Helper that converts regular char buffer to u16 unicode-like strings;
+ * notice that the unicode buffer requires to be at least len+1 in size.
+ */
+static inline void
+efi_str8_to_str16(efi_char16_t *str16, const char *str8, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++)
+		str16[i] = str8[i];
+
+	str16[i] = '\0';
+}
+
 int efivars_register(struct efivars *efivars,
 		     const struct efivar_operations *ops,
 		     struct kobject *kobject);
-- 
2.36.0