From 478a0cff698409224330ea9e25eb332220b55dbb Mon Sep 17 00:00:00 2001
From: Jeremy Cline <jcline@redhat.com>
Date: Mon, 30 Sep 2019 21:22:47 +0000
Subject: [PATCH 1/3] security: lockdown: expose a hook to lock the kernel down
In order to automatically lock down kernels running on UEFI machines
booted in Secure Boot mode, expose the lock_kernel_down() hook.
Signed-off-by: Jeremy Cline <jcline@redhat.com>
---
include/linux/lsm_hooks.h | 8 ++++++++
include/linux/security.h | 5 +++++
security/lockdown/lockdown.c | 1 +
security/security.c | 6 ++++++
4 files changed, 20 insertions(+)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index a3763247547c..8d76d1f153ed 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1454,6 +1454,12 @@
* code execution in kernel space should be permitted.
*
* @what: kernel feature being accessed
+ *
+ * @lock_kernel_down
+ * Put the kernel into lock-down mode.
+ *
+ * @where: Where the lock-down is originating from (e.g. command line option)
+ * @level: The lock-down level (can only increase)
*/
union security_list_options {
int (*binder_set_context_mgr)(struct task_struct *mgr);
@@ -1818,6 +1824,7 @@ union security_list_options {
void (*bpf_prog_free_security)(struct bpf_prog_aux *aux);
#endif /* CONFIG_BPF_SYSCALL */
int (*locked_down)(enum lockdown_reason what);
+ int (*lock_kernel_down)(const char *where, enum lockdown_reason level);
};
struct security_hook_heads {
@@ -2060,6 +2067,7 @@ struct security_hook_heads {
struct hlist_head bpf_prog_free_security;
#endif /* CONFIG_BPF_SYSCALL */
struct hlist_head locked_down;
+ struct hlist_head lock_kernel_down;
} __randomize_layout;
/*
diff --git a/include/linux/security.h b/include/linux/security.h
index a8d59d612d27..467b9ccdf993 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -442,6 +442,7 @@ int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
int security_locked_down(enum lockdown_reason what);
+int security_lock_kernel_down(const char *where, enum lockdown_reason level);
#else /* CONFIG_SECURITY */
static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
@@ -1269,6 +1270,10 @@ static inline int security_locked_down(enum lockdown_reason what)
{
return 0;
}
+static inline int security_lock_kernel_down(const char *where, enum lockdown_reason level)
+{
+ return 0;
+}
#endif /* CONFIG_SECURITY */
#ifdef CONFIG_SECURITY_NETWORK
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 8a10b43daf74..72a623075749 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -97,6 +97,7 @@ static int lockdown_is_locked_down(enum lockdown_reason what)
static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
+ LSM_HOOK_INIT(lock_kernel_down, lock_kernel_down),
};
static int __init lockdown_lsm_init(void)
diff --git a/security/security.c b/security/security.c
index 1bc000f834e2..1506b95427cf 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2404,3 +2404,9 @@ int security_locked_down(enum lockdown_reason what)
return call_int_hook(locked_down, 0, what);
}
EXPORT_SYMBOL(security_locked_down);
+
+int security_lock_kernel_down(const char *where, enum lockdown_reason level)
+{
+ return call_int_hook(lock_kernel_down, 0, where, level);
+}
+EXPORT_SYMBOL(security_lock_kernel_down);
--
2.21.0
From b5123d0553f4ed5e734f6457696cdd30228d1eee Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Tue, 27 Feb 2018 10:04:55 +0000
Subject: [PATCH 2/3] efi: Add an EFI_SECURE_BOOT flag to indicate secure
boot mode
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
[Rebased for context; efi_is_table_address was moved to arch/x86]
Signed-off-by: Jeremy Cline <jcline@redhat.com>
---
arch/x86/kernel/setup.c | 14 +-----------
drivers/firmware/efi/Makefile | 1 +
drivers/firmware/efi/secureboot.c | 38 +++++++++++++++++++++++++++++++
include/linux/efi.h | 18 ++++++++++-----
4 files changed, 52 insertions(+), 19 deletions(-)
create mode 100644 drivers/firmware/efi/secureboot.c
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index bbe35bf879f5..7e528b6af86b 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1179,19 +1179,7 @@ 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();
diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
index 4ac2de4dfa72..195b078a423c 100644
--- a/drivers/firmware/efi/Makefile
+++ b/drivers/firmware/efi/Makefile
@@ -24,6 +24,7 @@ obj-$(CONFIG_EFI_FAKE_MEMMAP) += fake_mem.o
obj-$(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
diff --git a/drivers/firmware/efi/secureboot.c b/drivers/firmware/efi/secureboot.c
new file mode 100644
index 000000000000..9070055de0a1
--- /dev/null
+++ b/drivers/firmware/efi/secureboot.c
@@ -0,0 +1,38 @@
+/* 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_warning("Secure boot could not be determined (mode %u)\n",
+ mode);
+ break;
+ }
+ }
+}
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 21d81021c1f4..758ec061d03b 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1204,6 +1204,14 @@ extern int __init efi_setup_pcdp_console(char *);
#define EFI_DBG 8 /* Print additional debug info at runtime */
#define EFI_NX_PE_DATA 9 /* Can runtime data regions be mapped non-executable? */
#define EFI_MEM_ATTR 10 /* Did firmware publish an EFI_MEMORY_ATTRIBUTES table? */
+#define EFI_SECURE_BOOT 11 /* 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
/*
@@ -1214,6 +1222,8 @@ static inline bool efi_enabled(int feature)
return test_bit(feature, &efi.flags) != 0;
}
extern void efi_reboot(enum reboot_mode reboot_mode, const char *__unused);
+
+extern void __init efi_set_secure_boot(enum efi_secureboot_mode mode);
#else
static inline bool efi_enabled(int feature)
{
@@ -1227,6 +1237,8 @@ efi_capsule_pending(int *reset_type)
{
return false;
}
+
+static inline void efi_set_secure_boot(enum efi_secureboot_mode mode) {}
#endif
extern int efi_status_to_err(efi_status_t status);
@@ -1619,12 +1631,6 @@ static inline bool efi_runtime_disabled(void) { return true; }
extern void efi_call_virt_check_flags(unsigned long flags, const char *call);
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,
-};
enum efi_secureboot_mode efi_get_secureboot(efi_system_table_t *sys_table);
#ifdef CONFIG_RESET_ATTACK_MITIGATION
--
2.21.0
From 15368f76d4997912318d35c52bfeb9041d85098e Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Mon, 30 Sep 2019 21:28:16 +0000
Subject: [PATCH 3/3] efi: Lock down the kernel if booted in secure boot mode
UEFI Secure Boot provides a mechanism for ensuring that the firmware
will only load signed bootloaders and kernels. Certain use cases may
also require that all kernel modules also be signed. Add a
configuration option that to lock down the kernel - which includes
requiring validly signed modules - if the kernel is secure-booted.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeremy Cline <jcline@redhat.com>
---
arch/x86/kernel/setup.c | 8 ++++++++
security/lockdown/Kconfig | 13 +++++++++++++
2 files changed, 21 insertions(+)
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 77ea96b794bd..a119e1bc9623 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -73,6 +73,7 @@
#include <linux/jiffies.h>
#include <linux/mem_encrypt.h>
#include <linux/sizes.h>
+#include <linux/security.h>
#include <linux/usb/xhci-dbgp.h>
#include <video/edid.h>
@@ -1027,6 +1028,13 @@ void __init setup_arch(char **cmdline_p)
if (efi_enabled(EFI_BOOT))
efi_init();
+ efi_set_secure_boot(boot_params.secure_boot);
+
+#ifdef CONFIG_LOCK_DOWN_IN_EFI_SECURE_BOOT
+ if (efi_enabled(EFI_SECURE_BOOT))
+ security_lock_kernel_down("EFI Secure Boot mode", LOCKDOWN_CONFIDENTIALITY_MAX);
+#endif
+
dmi_setup();
/*
diff --git a/security/lockdown/Kconfig b/security/lockdown/Kconfig
index e84ddf484010..d0501353a4b9 100644
--- a/security/lockdown/Kconfig
+++ b/security/lockdown/Kconfig
@@ -16,6 +16,19 @@ config SECURITY_LOCKDOWN_LSM_EARLY
subsystem is fully initialised. If enabled, lockdown will
unconditionally be called before any other LSMs.
+config LOCK_DOWN_IN_EFI_SECURE_BOOT
+ bool "Lock down the kernel in EFI Secure Boot mode"
+ default n
+ depends on EFI && SECURITY_LOCKDOWN_LSM_EARLY
+ help
+ UEFI Secure Boot provides a mechanism for ensuring that the firmware
+ will only load signed bootloaders and kernels. Secure boot mode may
+ be determined from EFI variables provided by the system firmware if
+ not indicated by the boot parameters.
+
+ Enabling this option results in kernel lockdown being triggered if
+ EFI Secure Boot is set.
+
choice
prompt "Kernel default lockdown mode"
default LOCK_DOWN_KERNEL_FORCE_NONE
--
2.21.0