From 416581e486798cbe3e2b3306faee7d7e9bf3c3d4 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ardb@kernel.org>
Date: Mon, 20 Jun 2022 11:35:37 +0200
Subject: [PATCH] efi: efibc: avoid efivar API for setting variables

Avoid abusing the efivar API by passing locally instantiated
efivar_entry structs into efivar_set_entry_safe(), rather than using the
API as intended. Instead, just call efi.set_variable() directly.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/Kconfig |  1 +
 drivers/firmware/efi/efibc.c | 78 ++++++++++++++----------------------
 2 files changed, 31 insertions(+), 48 deletions(-)

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 7aa4717cdcac..6fd4414c4836 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -145,6 +145,7 @@ config EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER
 
 config EFI_BOOTLOADER_CONTROL
 	tristate "EFI Bootloader Control"
+	select UCS2_STRING
 	default n
 	help
 	  This module installs a reboot hook, such that if reboot() is
diff --git a/drivers/firmware/efi/efibc.c b/drivers/firmware/efi/efibc.c
index 15a47539dc56..8ced7af8e56d 100644
--- a/drivers/firmware/efi/efibc.c
+++ b/drivers/firmware/efi/efibc.c
@@ -10,69 +10,51 @@
 #include <linux/module.h>
 #include <linux/reboot.h>
 #include <linux/slab.h>
+#include <linux/ucs2_string.h>
 
-static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
+#define MAX_DATA_LEN	512
+
+static int efibc_set_variable(efi_char16_t *name, efi_char16_t *value,
+			      unsigned long len)
 {
-	size_t i;
+	efi_status_t status;
 
-	for (i = 0; i < strlen(str); i++)
-		str16[i] = str[i];
+	status = efi.set_variable(name, &LINUX_EFI_LOADER_ENTRY_GUID,
+				  EFI_VARIABLE_NON_VOLATILE
+				  | EFI_VARIABLE_BOOTSERVICE_ACCESS
+				  | EFI_VARIABLE_RUNTIME_ACCESS,
+				  len * sizeof(efi_char16_t), value);
 
-	str16[i] = '\0';
-}
-
-static int efibc_set_variable(const char *name, const char *value)
-{
-	int ret;
-	efi_guid_t guid = LINUX_EFI_LOADER_ENTRY_GUID;
-	struct efivar_entry *entry;
-	size_t size = (strlen(value) + 1) * sizeof(efi_char16_t);
-
-	if (size > sizeof(entry->var.Data)) {
-		pr_err("value is too large (%zu bytes) for '%s' EFI variable\n", size, name);
-		return -EINVAL;
+	if (status != EFI_SUCCESS) {
+		pr_err("failed to set EFI variable: 0x%lx\n", status);
+		return -EIO;
 	}
-
-	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
-	if (!entry) {
-		pr_err("failed to allocate efivar entry for '%s' EFI variable\n", name);
-		return -ENOMEM;
-	}
-
-	efibc_str_to_str16(name, entry->var.VariableName);
-	efibc_str_to_str16(value, (efi_char16_t *)entry->var.Data);
-	memcpy(&entry->var.VendorGuid, &guid, sizeof(guid));
-
-	ret = efivar_entry_set_safe(entry->var.VariableName,
-				    entry->var.VendorGuid,
-				    EFI_VARIABLE_NON_VOLATILE
-				    | EFI_VARIABLE_BOOTSERVICE_ACCESS
-				    | EFI_VARIABLE_RUNTIME_ACCESS,
-				    false, size, entry->var.Data);
-
-	if (ret)
-		pr_err("failed to set %s EFI variable: 0x%x\n",
-		       name, ret);
-
-	kfree(entry);
-	return ret;
+	return 0;
 }
 
 static int efibc_reboot_notifier_call(struct notifier_block *notifier,
 				      unsigned long event, void *data)
 {
-	const char *reason = "shutdown";
+	efi_char16_t *reason = event == SYS_RESTART ? L"reboot"
+						    : L"shutdown";
+	const u8 *str = data;
+	efi_char16_t *wdata;
+	unsigned long l;
 	int ret;
 
-	if (event == SYS_RESTART)
-		reason = "reboot";
-
-	ret = efibc_set_variable("LoaderEntryRebootReason", reason);
+	ret = efibc_set_variable(L"LoaderEntryRebootReason", reason,
+				 ucs2_strlen(reason));
 	if (ret || !data)
 		return NOTIFY_DONE;
 
-	efibc_set_variable("LoaderEntryOneShot", (char *)data);
+	wdata = kmalloc(MAX_DATA_LEN * sizeof(efi_char16_t), GFP_KERNEL);
+	for (l = 0; l < MAX_DATA_LEN - 1 && str[l] != '\0'; l++)
+		wdata[l] = str[l];
+	wdata[l] = L'\0';
 
+	efibc_set_variable(L"LoaderEntryOneShot", wdata, l);
+
+	kfree(wdata);
 	return NOTIFY_DONE;
 }
 
@@ -84,7 +66,7 @@ static int __init efibc_init(void)
 {
 	int ret;
 
-	if (!efivars_kobject() || !efivar_supports_writes())
+	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_SET_VARIABLE))
 		return -ENODEV;
 
 	ret = register_reboot_notifier(&efibc_reboot_notifier);