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Message-ID: <148587562967.4026.18171897997650345605.stgit@warthog.procyon.org.uk>
Date: Tue, 31 Jan 2017 15:13:49 +0000
From: David Howells <dhowells@...hat.com>
To: matt@...eblueprint.co.uk, ard.biesheuvel@...aro.org
Cc: linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
dhowells@...hat.com, linux-security-module@...r.kernel.org,
keyrings@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 4/7] efi: Get the secure boot status [ver #7]
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@...ner.de>
Signed-off-by: David Howells <dhowells@...hat.com>
---
Documentation/x86/zero-page.txt | 2 +
arch/x86/boot/compressed/eboot.c | 6 +++
arch/x86/include/uapi/asm/bootparam.h | 3 +
arch/x86/kernel/asm-offsets.c | 1
drivers/firmware/efi/libstub/Makefile | 2 -
drivers/firmware/efi/libstub/arm-stub.c | 63 +++--------------------------
drivers/firmware/efi/libstub/secureboot.c | 63 +++++++++++++++++++++++++++++
include/linux/efi.h | 8 ++++
8 files changed, 89 insertions(+), 59 deletions(-)
create mode 100644 drivers/firmware/efi/libstub/secureboot.c
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..57c2c9c71e53 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -988,6 +988,12 @@ 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..62d6904da800
--- /dev/null
+++ b/drivers/firmware/efi/libstub/secureboot.c
@@ -0,0 +1,63 @@
+/*
+ * Secure boot handling.
+ *
+ * Copyright (C) 2013,2014 Linaro Limited
+ * Roy Franz <roy.franz@...aro.org
+ * Copyright (C) 2013 Red Hat, Inc.
+ * Mark Salter <msalter@...hat.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 58c9dd48f42a..1c200cdbdc05 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():
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