[PATCH 2/2] efi: introduce EFI_KERNEL_LOCK_DOWN_IN_SECURE_BOOT

Hamza Mahfooz
2025-06-26T22:13:00Z

Add a kernel configuration option to lock down the kernel, to restrict
userspace's ability to modify the running kernel when Secure Boot is
enabled.

Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
---
drivers/firmware/efi/Kconfig | 10 ++++++++++
drivers/firmware/efi/efi.c | 9 +++++++++
2 files changed, 19 insertions(+)

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 5fe61b9ab5f9..4e827354e919 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -248,6 +248,16 @@ config EFI_DISABLE_RUNTIME

This default can be overridden by using the efi=runtime option.

+config EFI_KERNEL_LOCK_DOWN_IN_SECURE_BOOT
+ bool "Lock down the kernel in EFI Secure Boot mode"
+ default n
+ depends on EFI
+ depends on SECURITY_LOCKDOWN_LSM
+ select SECURITY_LOCKDOWN_LSM_EARLY
+ help
+ Enabling this option results in kernel lockdown being
+ set in integrity mode if EFI Secure Boot is enabled.
+
config EFI_COCO_SECRET
bool "EFI Confidential Computing Secret Area Support"
help
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 7309394b8fc9..b7a5fc79b065 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -427,6 +427,15 @@ static int __init efisubsys_init(void)
}
}

+#ifdef CONFIG_EFI_KERNEL_LOCK_DOWN_IN_SECURE_BOOT
+ if (efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) {
+ if (efi_get_secureboot_mode(efi.get_variable) ==
+ efi_secureboot_mode_enabled)
+ security_lock_kernel_down("EFI Secure Boot",
+ LOCKDOWN_INTEGRITY_MAX);
+ }
+#endif
+
if (efi_rt_services_supported(EFI_RT_SUPPORTED_TIME_SERVICES))
platform_device_register_simple("rtc-efi", 0, NULL, 0);

--
2.49.0