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@xxxxxxxxxx>
---
arch/x86/Kconfig | 12 ++++++++++++
arch/x86/kernel/setup.c | 7 +++++++
kernel/module.c | 2 +-
3 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bada636d1065..5b19997d88d0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1786,6 +1786,18 @@ config EFI_MIXED
If unsure, say N.
+config EFI_SECURE_BOOT_LOCK_DOWN
+ def_bool n
+ depends on EFI
+ prompt "Lock down the kernel when UEFI Secure Boot is enabled"
+ ---help---
+ 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 and that
+ userspace is prevented from directly changing the running kernel
+ image. Say Y here to automatically lock down the kernel when a
+ system boots with UEFI Secure Boot enabled.
+
config SECCOMP
def_bool y
prompt "Enable seccomp to safely compute untrusted bytecode"
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 9c337b0e8ba7..9521acce8378 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -69,6 +69,7 @@
#include <linux/crash_dump.h>
#include <linux/tboot.h>
#include <linux/jiffies.h>
+#include <linux/security.h>
#include <video/edid.h>
@@ -1160,6 +1161,12 @@ void __init setup_arch(char **cmdline_p)
io_delay_init();
+ if (boot_params.secure_boot &&
+ IS_ENABLED(CONFIG_EFI_SECURE_BOOT_LOCK_DOWN)) {
+ lock_kernel_down();
+ pr_info("Secure boot enabled\n");
+ }
+
/*
* Parse the ACPI tables for possible boot-time SMP configuration.
*/
diff --git a/kernel/module.c b/kernel/module.c
index f57dd63186e6..2a021c340efd 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2744,7 +2744,7 @@ static int module_sig_check(struct load_info *info, int flags)
}
/* Not having a signature is only an error if we're strict. */
- if (err == -ENOKEY && !sig_enforce)
+ if (err == -ENOKEY && !sig_enforce && !kernel_is_locked_down())
err = 0;
return err;
--
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