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From: Ben Hutchings <ben@decadent.org.uk>
Date: Tue, 10 Sep 2019 11:54:28 +0100
Subject: efi: Lock down the kernel if booted in secure boot mode
Based on an earlier patch by David Howells, who wrote the following
description:
> 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: Ben Hutchings <ben@decadent.org.uk>
[Salvatore Bonaccorso: After fixing https://bugs.debian.org/956197 the
help text for LOCK_DOWN_IN_EFI_SECURE_BOOT needs to be adjusted to
mention that lockdown is triggered in integrity mode]
Signed-off-by: Salvatore Bonaccorso <carnil@debian.org>
---
arch/x86/kernel/setup.c | 4 ++--
drivers/firmware/efi/secureboot.c | 3 +++
include/linux/security.h | 6 ++++++
security/lockdown/Kconfig | 15 +++++++++++++++
security/lockdown/lockdown.c | 2 +-
5 files changed, 27 insertions(+), 3 deletions(-)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1031,6 +1031,8 @@ void __init setup_arch(char **cmdline_p)
if (efi_enabled(EFI_BOOT))
efi_init();
+ efi_set_secure_boot(boot_params.secure_boot);
+
x86_init.resources.dmi_setup();
/*
@@ -1200,8 +1202,6 @@ void __init setup_arch(char **cmdline_p)
/* Allocate bigger log buffer */
setup_log_buf(1);
- efi_set_secure_boot(boot_params.secure_boot);
-
reserve_initrd();
acpi_table_upgrade();
--- a/drivers/firmware/efi/secureboot.c
+++ b/drivers/firmware/efi/secureboot.c
@@ -15,6 +15,7 @@
#include <linux/efi.h>
#include <linux/kernel.h>
#include <linux/printk.h>
+#include <linux/security.h>
/*
* Decide what to do when UEFI secure boot mode is enabled.
@@ -28,6 +29,10 @@ void __init efi_set_secure_boot(enum efi
break;
case efi_secureboot_mode_enabled:
set_bit(EFI_SECURE_BOOT, &efi.flags);
+#ifdef CONFIG_LOCK_DOWN_IN_EFI_SECURE_BOOT
+ lock_kernel_down("EFI Secure Boot",
+ LOCKDOWN_INTEGRITY_MAX);
+#endif
pr_info("Secure boot enabled\n");
break;
default:
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -481,6 +481,7 @@ int security_inode_notifysecctx(struct i
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 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)
@@ -1381,6 +1382,11 @@ static inline int security_locked_down(e
{
return 0;
}
+static inline int
+lock_kernel_down(const char *where, enum lockdown_reason level)
+{
+ return -EOPNOTSUPP;
+}
#endif /* CONFIG_SECURITY */
#if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
--- a/security/lockdown/Kconfig
+++ b/security/lockdown/Kconfig
@@ -45,3 +45,18 @@ config LOCK_DOWN_KERNEL_FORCE_CONFIDENTI
disabled.
endchoice
+
+config LOCK_DOWN_IN_EFI_SECURE_BOOT
+ bool "Lock down the kernel in EFI Secure Boot mode"
+ default n
+ depends on SECURITY_LOCKDOWN_LSM
+ depends on EFI
+ select 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 in integrity mode if EFI Secure Boot is set.
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -23,7 +23,7 @@ static const enum lockdown_reason lockdo
/*
* Put the kernel into lock-down mode.
*/
-static int lock_kernel_down(const char *where, enum lockdown_reason level)
+int lock_kernel_down(const char *where, enum lockdown_reason level)
{
if (kernel_locked_down >= level)
return -EPERM;
|
