efi: Get and store the secure boot status

Get the firmware's secure-boot status in the kernel boot wrapper and stash
it somewhere that the main kernel image can find.

The efi_get_secureboot() function is extracted from the ARM stub and (a)
generalised so that it can be called from x86 and (b) made to use
efi_call_runtime() so that it can be run in mixed-mode.

For x86, it is stored in boot_params and can be overridden by the boot
loader or kexec.  This allows secure-boot mode to be passed on to a new
kernel.

Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1486380166-31868-5-git-send-email-ard.biesheuvel@linaro.org
[ Small readability edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

8 files changed, 88 insertions, 59 deletions

diff --git a/Documentation/x86/zero-page.txt b/Documentation/x86/zero-page.txt
index 95a4d34af3fd..b8527c6b7646 100644
--- a/Documentation/x86/zero-page.txt
+++ b/Documentation/x86/zero-page.txt
@@ -31,6 +31,8 @@ Offset	Proto	Name		Meaning
 1E9/001 ALL     eddbuf_entries  Number of entries in eddbuf (below)
 1EA/001 ALL     edd_mbr_sig_buf_entries Number of entries in edd_mbr_sig_buffer
                                 (below)
+1EB/001 ALL     kbd_status      Numlock is enabled
+1EC/001 ALL     secure_boot     Secure boot is enabled in the firmware
 1EF/001 ALL     sentinel        Used to detect broken bootloaders
 290/040 ALL     edd_mbr_sig_buffer EDD MBR signatures
 2D0/A00 ALL     e820_map        E820 memory map table
diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index f99978db6b6f..801c7a158e55 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -988,6 +988,13 @@ struct boot_params *efi_main(struct efi_config *c,
         else
                 setup_boot_services32(efi_early);
 
+        /*
+         * If the boot loader gave us a value for secure_boot then we use that,
+         * otherwise we ask the BIOS.
+         */
+        if (boot_params->secure_boot == efi_secureboot_mode_unset)
+                boot_params->secure_boot = efi_get_secureboot(sys_table);
+
         setup_graphics(boot_params);
 
         setup_efi_pci(boot_params);
diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
index b10bf319ed20..5138dacf8bb8 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -135,7 +135,8 @@ struct boot_params {
         __u8  eddbuf_entries;                           /* 0x1e9 */
         __u8  edd_mbr_sig_buf_entries;                  /* 0x1ea */
         __u8  kbd_status;                               /* 0x1eb */
-        __u8  _pad5[3];                                 /* 0x1ec */
+        __u8  secure_boot;                              /* 0x1ec */
+        __u8  _pad5[2];                                 /* 0x1ed */
         /*
          * The sentinel is set to a nonzero value (0xff) in header.S.
          *
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index c62e015b126c..de827d6ac8c2 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -81,6 +81,7 @@ void common(void) {
 
         BLANK();
         OFFSET(BP_scratch, boot_params, scratch);
+        OFFSET(BP_secure_boot, boot_params, secure_boot);
         OFFSET(BP_loadflags, boot_params, hdr.loadflags);
         OFFSET(BP_hardware_subarch, boot_params, hdr.hardware_subarch);
         OFFSET(BP_version, boot_params, hdr.version);
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 33e0e2f1a730..f7425960f6a5 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -28,7 +28,7 @@ OBJECT_FILES_NON_STANDARD	:= y
 # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
 KCOV_INSTRUMENT                 := n
 
-lib-y                           := efi-stub-helper.o gop.o
+lib-y                           := efi-stub-helper.o gop.o secureboot.o
 
 # include the stub's generic dependencies from lib/ when building for ARM/arm64
 arm-deps := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c sort.c
diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 6fca48c9e054..d4056c6be1ec 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -20,52 +20,6 @@
 
 bool __nokaslr;
 
-static int efi_get_secureboot(efi_system_table_t *sys_table_arg)
-{
-        static efi_char16_t const sb_var_name[] = {
-                'S', 'e', 'c', 'u', 'r', 'e', 'B', 'o', 'o', 't', 0 };
-        static efi_char16_t const sm_var_name[] = {
-                'S', 'e', 't', 'u', 'p', 'M', 'o', 'd', 'e', 0 };
-
-        efi_guid_t var_guid = EFI_GLOBAL_VARIABLE_GUID;
-        efi_get_variable_t *f_getvar = sys_table_arg->runtime->get_variable;
-        u8 val;
-        unsigned long size = sizeof(val);
-        efi_status_t status;
-
-        status = f_getvar((efi_char16_t *)sb_var_name, (efi_guid_t *)&var_guid,
-                          NULL, &size, &val);
-
-        if (status != EFI_SUCCESS)
-                goto out_efi_err;
-
-        if (val == 0)
-                return 0;
-
-        status = f_getvar((efi_char16_t *)sm_var_name, (efi_guid_t *)&var_guid,
-                          NULL, &size, &val);
-
-        if (status != EFI_SUCCESS)
-                goto out_efi_err;
-
-        if (val == 1)
-                return 0;
-
-        return 1;
-
-out_efi_err:
-        switch (status) {
-        case EFI_NOT_FOUND:
-                return 0;
-        case EFI_DEVICE_ERROR:
-                return -EIO;
-        case EFI_SECURITY_VIOLATION:
-                return -EACCES;
-        default:
-                return -EINVAL;
-        }
-}
-
 efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg,
                              void *__image, void **__fh)
 {
@@ -157,7 +111,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
         efi_guid_t loaded_image_proto = LOADED_IMAGE_PROTOCOL_GUID;
         unsigned long reserve_addr = 0;
         unsigned long reserve_size = 0;
-        int secure_boot = 0;
+        enum efi_secureboot_mode secure_boot;
         struct screen_info *si;
 
         /* Check if we were booted by the EFI firmware */
@@ -227,19 +181,14 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
                 pr_efi_err(sys_table, "Failed to parse EFI cmdline options\n");
 
         secure_boot = efi_get_secureboot(sys_table);
-        if (secure_boot > 0)
-                pr_efi(sys_table, "UEFI Secure Boot is enabled.\n");
-
-        if (secure_boot < 0) {
-                pr_efi_err(sys_table,
-                        "could not determine UEFI Secure Boot status.\n");
-        }
 
         /*
-         * Unauthenticated device tree data is a security hazard, so
-         * ignore 'dtb=' unless UEFI Secure Boot is disabled.
+         * Unauthenticated device tree data is a security hazard, so ignore
+         * 'dtb=' unless UEFI Secure Boot is disabled.  We assume that secure
+         * boot is enabled if we can't determine its state.
          */
-        if (secure_boot != 0 && strstr(cmdline_ptr, "dtb=")) {
+        if (secure_boot != efi_secureboot_mode_disabled &&
+            strstr(cmdline_ptr, "dtb=")) {
                 pr_efi(sys_table, "Ignoring DTB from command line.\n");
         } else {
                 status = handle_cmdline_files(sys_table, image, cmdline_ptr,
diff --git a/drivers/firmware/efi/libstub/secureboot.c b/drivers/firmware/efi/libstub/secureboot.c
new file mode 100644
index 000000000000..b20b8b460d77
--- /dev/null
+++ b/drivers/firmware/efi/libstub/secureboot.c
@@ -0,0 +1,61 @@
+/*
+ * Secure boot handling.
+ *
+ * Copyright (C) 2013,2014 Linaro Limited
+ *     Roy Franz <roy.franz@linaro.org
+ * Copyright (C) 2013 Red Hat, Inc.
+ *     Mark Salter <msalter@redhat.com>
+ *
+ * This file is part of the Linux kernel, and is made available under the
+ * terms of the GNU General Public License version 2.
+ */
+#include <linux/efi.h>
+#include <asm/efi.h>
+
+/* BIOS variables */
+static const efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
+static const efi_char16_t const efi_SecureBoot_name[] = {
+        'S', 'e', 'c', 'u', 'r', 'e', 'B', 'o', 'o', 't', 0
+};
+static const efi_char16_t const efi_SetupMode_name[] = {
+        'S', 'e', 't', 'u', 'p', 'M', 'o', 'd', 'e', 0
+};
+
+#define get_efi_var(name, vendor, ...) \
+        efi_call_runtime(get_variable, \
+                         (efi_char16_t *)(name), (efi_guid_t *)(vendor), \
+                         __VA_ARGS__);
+
+/*
+ * Determine whether we're in secure boot mode.
+ */
+enum efi_secureboot_mode efi_get_secureboot(efi_system_table_t *sys_table_arg)
+{
+        u8 secboot, setupmode;
+        unsigned long size;
+        efi_status_t status;
+
+        size = sizeof(secboot);
+        status = get_efi_var(efi_SecureBoot_name, &efi_variable_guid,
+                             NULL, &size, &secboot);
+        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;
+
+        pr_efi(sys_table_arg, "UEFI Secure Boot is enabled.\n");
+        return efi_secureboot_mode_enabled;
+
+out_efi_err:
+        pr_efi_err(sys_table_arg, "Could not determine UEFI Secure Boot status.\n");
+        if (status == EFI_NOT_FOUND)
+                return efi_secureboot_mode_disabled;
+        return efi_secureboot_mode_unknown;
+}
diff --git a/include/linux/efi.h b/include/linux/efi.h
index d00538a65899..94d34e0be24f 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1480,6 +1480,14 @@ efi_status_t efi_setup_gop(efi_system_table_t *sys_table_arg,
 bool efi_runtime_disabled(void);
 extern void efi_call_virt_check_flags(unsigned long flags, const char *call);
 
+enum efi_secureboot_mode {
+        efi_secureboot_mode_unset,
+        efi_secureboot_mode_unknown,
+        efi_secureboot_mode_disabled,
+        efi_secureboot_mode_enabled,
+};
+enum efi_secureboot_mode efi_get_secureboot(efi_system_table_t *sys_table);
+
 /*
  * Arch code can implement the following three template macros, avoiding
  * reptition for the void/non-void return cases of {__,}efi_call_virt():