efi: generalize efi_get_secureboot

Generalize the efi_get_secureboot() function so not only efistub but also
other subsystems can use it.

Note that the MokSbState handling is not factored out: the variable is
boot time only, and so it cannot be parameterized as easily. Also, the
IMA code will switch to this version in a future patch, and it does not
incorporate the MokSbState exception in the first place.

Note that the new efi_get_secureboot_mode() helper treats any failures
to read SetupMode as setup mode being disabled.
Co-developed-by: Chester Lin <clin@suse.com>
Signed-off-by: Chester Lin <clin@suse.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/x86/boot/compressed/Makefile

@@ -35,7 +35,7 @@ cflags-$(CONFIG_X86_32) := -march=i386
 cflags-$(CONFIG_X86_64) := -mcmodel=small -mno-red-zone
 KBUILD_CFLAGS += $(cflags-y)
 KBUILD_CFLAGS += -mno-mmx -mno-sse
-KBUILD_CFLAGS += -ffreestanding
+KBUILD_CFLAGS += -ffreestanding -fshort-wchar
 KBUILD_CFLAGS += -fno-stack-protector
 KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
 KBUILD_CFLAGS += $(call cc-disable-warning, gnu)

drivers/firmware/efi/libstub/efistub.h

@@ -848,4 +848,6 @@ asmlinkage void __noreturn efi_enter_kernel(unsigned long entrypoint,
 
 void efi_handle_post_ebs_state(void);
 
+enum efi_secureboot_mode efi_get_secureboot(void);
+
 #endif

drivers/firmware/efi/libstub/secureboot.c

@@ -12,15 +12,16 @@
 
 #include "efistub.h"
 
-/* BIOS variables */
-static const efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
-static const efi_char16_t efi_SecureBoot_name[] = L"SecureBoot";
-static const efi_char16_t efi_SetupMode_name[] = L"SetupMode";
-
 /* SHIM variables */
 static const efi_guid_t shim_guid = EFI_SHIM_LOCK_GUID;
 static const efi_char16_t shim_MokSBState_name[] = L"MokSBState";
 
+static efi_status_t get_var(efi_char16_t *name, efi_guid_t *vendor, u32 *attr,
+			    unsigned long *data_size, void *data)
+{
+	return get_efi_var(name, vendor, attr, data_size, data);
+}
+
 /*
  * Determine whether we're in secure boot mode.
  *
@@ -30,26 +31,18 @@ static const efi_char16_t shim_MokSBState_name[] = L"MokSBState";
 enum efi_secureboot_mode efi_get_secureboot(void)
 {
 	u32 attr;
-	u8 secboot, setupmode, moksbstate;
 	unsigned long size;
+	enum efi_secureboot_mode mode;
 	efi_status_t status;
+	u8 moksbstate;
 
-	size = sizeof(secboot);
-	status = get_efi_var(efi_SecureBoot_name, &efi_variable_guid,
-			     NULL, &size, &secboot);
-	if (status == EFI_NOT_FOUND)
-		return efi_secureboot_mode_disabled;
-	if (status != EFI_SUCCESS)
-		goto out_efi_err;
-
-	size = sizeof(setupmode);
-	status = get_efi_var(efi_SetupMode_name, &efi_variable_guid,
-			     NULL, &size, &setupmode);
-	if (status != EFI_SUCCESS)
-		goto out_efi_err;
-
-	if (secboot == 0 || setupmode == 1)
-		return efi_secureboot_mode_disabled;
+	mode = efi_get_secureboot_mode(get_var);
+	if (mode == efi_secureboot_mode_unknown) {
+		efi_err("Could not determine UEFI Secure Boot status.\n");
+		return efi_secureboot_mode_unknown;
+	}
+	if (mode != efi_secureboot_mode_enabled)
+		return mode;
 
 	/*
 	 * See if a user has put the shim into insecure mode. If so, and if the
@@ -69,8 +62,4 @@ enum efi_secureboot_mode efi_get_secureboot(void)
 secure_boot_enabled:
 	efi_info("UEFI Secure Boot is enabled.\n");
 	return efi_secureboot_mode_enabled;
-
-out_efi_err:
-	efi_err("Could not determine UEFI Secure Boot status.\n");
-	return efi_secureboot_mode_unknown;
 }

include/linux/efi.h

@@ -1089,7 +1089,28 @@ enum efi_secureboot_mode {
 	efi_secureboot_mode_disabled,
 	efi_secureboot_mode_enabled,
 };
-enum efi_secureboot_mode efi_get_secureboot(void);
+
+static inline
+enum efi_secureboot_mode efi_get_secureboot_mode(efi_get_variable_t *get_var)
+{
+	u8 secboot, setupmode = 0;
+	efi_status_t status;
+	unsigned long size;
+
+	size = sizeof(secboot);
+	status = get_var(L"SecureBoot", &EFI_GLOBAL_VARIABLE_GUID, NULL, &size,
+			 &secboot);
+	if (status == EFI_NOT_FOUND)
+		return efi_secureboot_mode_disabled;
+	if (status != EFI_SUCCESS)
+		return efi_secureboot_mode_unknown;
+
+	size = sizeof(setupmode);
+	get_var(L"SetupMode", &EFI_GLOBAL_VARIABLE_GUID, NULL, &size, &setupmode);
+	if (secboot == 0 || setupmode == 1)
+		return efi_secureboot_mode_disabled;
+	return efi_secureboot_mode_enabled;
+}
 
 #ifdef CONFIG_RESET_ATTACK_MITIGATION
 void efi_enable_reset_attack_mitigation(void);