efi: Add an EFI_SECURE_BOOT flag to indicate secure boot mode

jira LE-2629
feature Additional SecureBoot patches for dynamic lockdown
commit 78c8af872660c31779951583b6f1ebf283d95985
commit-source https://salsa.debian.org/kernel-team/linux.git

UEFI machines can be booted in Secure Boot mode.  Add an EFI_SECURE_BOOT
flag that can be passed to efi_enabled() to find out whether secure boot is
enabled.

Move the switch-statement in x86's setup_arch() that inteprets the
secure_boot boot parameter to generic code and set the bit there.

Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
cc: linux-efi@vger.kernel.org
[rperier: Forward-ported to 5.5:
 - Use pr_warn()
 - Adjust context]
[bwh: Forward-ported to 5.6: adjust context]
[bwh: Forward-ported to 5.7:
 - Use the next available bit in efi.flags
 - Adjust context]
Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: dhowells

arch/x86/kernel/setup.c

@@ -1070,19 +1070,7 @@ void __init setup_arch(char **cmdline_p)
 	/* Allocate bigger log buffer */
 	setup_log_buf(1);
 
-	if (efi_enabled(EFI_BOOT)) {
-		switch (boot_params.secure_boot) {
-		case efi_secureboot_mode_disabled:
-			pr_info("Secure boot disabled\n");
-			break;
-		case efi_secureboot_mode_enabled:
-			pr_info("Secure boot enabled\n");
-			break;
-		default:
-			pr_info("Secure boot could not be determined\n");
-			break;
-		}
-	}
+	efi_set_secure_boot(boot_params.secure_boot);
 
 	reserve_initrd();
 

drivers/firmware/efi/Makefile

@@ -25,6 +25,7 @@ subdir-$(CONFIG_EFI_STUB)		+= libstub
 obj-$(CONFIG_EFI_BOOTLOADER_CONTROL)	+= efibc.o
 obj-$(CONFIG_EFI_TEST)			+= test/
 obj-$(CONFIG_EFI_DEV_PATH_PARSER)	+= dev-path-parser.o
+obj-$(CONFIG_EFI)			+= secureboot.o
 obj-$(CONFIG_APPLE_PROPERTIES)		+= apple-properties.o
 obj-$(CONFIG_EFI_RCI2_TABLE)		+= rci2-table.o
 obj-$(CONFIG_EFI_EMBEDDED_FIRMWARE)	+= embedded-firmware.o

drivers/firmware/efi/secureboot.c

@@ -0,0 +1,39 @@
+
+/* Core kernel secure boot support.
+ *
+ * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/efi.h>
+#include <linux/kernel.h>
+#include <linux/printk.h>
+
+/*
+ * Decide what to do when UEFI secure boot mode is enabled.
+ */
+void __init efi_set_secure_boot(enum efi_secureboot_mode mode)
+{
+	if (efi_enabled(EFI_BOOT)) {
+		switch (mode) {
+		case efi_secureboot_mode_disabled:
+			pr_info("Secure boot disabled\n");
+			break;
+		case efi_secureboot_mode_enabled:
+			set_bit(EFI_SECURE_BOOT, &efi.flags);
+			pr_info("Secure boot enabled\n");
+			break;
+		default:
+			pr_warn("Secure boot could not be determined (mode %u)\n",
+				mode);
+			break;
+		}
+	}
+}

include/linux/efi.h

@@ -876,6 +876,14 @@ static inline int efi_range_is_wc(unsigned long start, unsigned long len)
 #define EFI_MEM_ATTR		10	/* Did firmware publish an EFI_MEMORY_ATTRIBUTES table? */
 #define EFI_MEM_NO_SOFT_RESERVE	11	/* Is the kernel configured to ignore soft reservations? */
 #define EFI_PRESERVE_BS_REGIONS	12	/* Are EFI boot-services memory segments available? */
+#define EFI_SECURE_BOOT		13	/* Are we in Secure Boot mode? */
+
+enum efi_secureboot_mode {
+	efi_secureboot_mode_unset,
+	efi_secureboot_mode_unknown,
+	efi_secureboot_mode_disabled,
+	efi_secureboot_mode_enabled,
+};
 
 #ifdef CONFIG_EFI
 /*
@@ -900,6 +908,7 @@ static inline bool efi_rt_services_supported(unsigned int mask)
 	return (efi.runtime_supported_mask & mask) == mask;
 }
 extern void efi_find_mirror(void);
+extern void __init efi_set_secure_boot(enum efi_secureboot_mode mode);
 #else
 static inline bool efi_enabled(int feature)
 {
@@ -919,6 +928,7 @@ static inline bool efi_rt_services_supported(unsigned int mask)
 }
 
 static inline void efi_find_mirror(void) {}
+static inline void efi_set_secure_boot(enum efi_secureboot_mode mode) {}
 #endif
 
 extern int efi_status_to_err(efi_status_t status);
@@ -1137,13 +1147,6 @@ static inline bool efi_runtime_disabled(void) { return true; }
 extern void efi_call_virt_check_flags(unsigned long flags, const void *caller);
 extern unsigned long efi_call_virt_save_flags(void);
 
-enum efi_secureboot_mode {
-	efi_secureboot_mode_unset,
-	efi_secureboot_mode_unknown,
-	efi_secureboot_mode_disabled,
-	efi_secureboot_mode_enabled,
-};
-
 static inline
 enum efi_secureboot_mode efi_get_secureboot_mode(efi_get_variable_t *get_var)
 {