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>
Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name efi-lock-down-the-kernel-if-booted-in-secure-boot-mo.patch

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 5c2bc32778d1ab0424e443eb2679496da66d3ed0..9d9e7d6d0e2a61b676ee0562629d8a86129d688b 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1032,6 +1032,8 @@ 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();
 
        /*
@@ -1202,8 +1204,6 @@ 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();

diff --git a/drivers/firmware/efi/secureboot.c b/drivers/firmware/efi/secureboot.c
index b6620669e32bc53f95865e08e0e77e7dceafb0e2..8f2554291fb1fe456f2fbcc09758ebe1c2085c43 100644 (file)
--- 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_secureboot_mode mode)
                        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:

diff --git a/include/linux/security.h b/include/linux/security.h
index c33c95f409eb675fad864183df6420c4e01aa3fd..8a75beffc07df780cedde3d927f074f8213f0816 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -481,6 +481,7 @@ 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 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(enum lockdown_reason what)
 {
        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)

diff --git a/security/lockdown/Kconfig b/security/lockdown/Kconfig
index e84ddf48401010bcc0829a32db58e6f12bfdedcb..4175b50b1e6e18191eaf7253294c6387fcf929d8 100644 (file)
--- a/security/lockdown/Kconfig
+++ b/security/lockdown/Kconfig
@@ -45,3 +45,18 @@ config LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY
         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.

diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index a79b985e917ee642f1b9a7a8350b8a9fc26ff6c8..b1493ff44a990d4460ad24d6a7a51d9216a98e8b 100644 (file)
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -23,7 +23,7 @@ static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
 /*
  * 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;