From: Ard Biesheuvel ardb@kernel.org
commit 5f56a74cc0a6d9b9f8ba89cea29cd7c4774cb2b1 upstream.
We currently check the MokSBState variable to decide whether we should treat UEFI secure boot as being disabled, even if the firmware thinks otherwise. This is used by shim to indicate that it is not checking signatures on boot images. In the kernel, we use this to relax lockdown policies.
However, in cases where shim is not even being used, we don't want this variable to interfere with lockdown, given that the variable may be non-volatile and therefore persist across a reboot. This means setting it once will persistently disable lockdown checks on a given system.
So switch to the mirrored version of this variable, called MokSBStateRT, which is supposed to be volatile, and this is something we can check.
Cc: stable@vger.kernel.org # v4.19+ Signed-off-by: Ard Biesheuvel ardb@kernel.org Reviewed-by: Ilias Apalodimas ilias.apalodimas@linaro.org Reviewed-by: Peter Jones pjones@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/firmware/efi/libstub/secureboot.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- a/drivers/firmware/efi/libstub/secureboot.c +++ b/drivers/firmware/efi/libstub/secureboot.c @@ -14,7 +14,7 @@
/* SHIM variables */ static const efi_guid_t shim_guid = EFI_SHIM_LOCK_GUID; -static const efi_char16_t shim_MokSBState_name[] = L"MokSBState"; +static const efi_char16_t shim_MokSBState_name[] = L"MokSBStateRT";
static efi_status_t get_var(efi_char16_t *name, efi_guid_t *vendor, u32 *attr, unsigned long *data_size, void *data) @@ -43,8 +43,8 @@ enum efi_secureboot_mode efi_get_secureb
/* * See if a user has put the shim into insecure mode. If so, and if the - * variable doesn't have the runtime attribute set, we might as well - * honor that. + * variable doesn't have the non-volatile attribute set, we might as + * well honor that. */ size = sizeof(moksbstate); status = get_efi_var(shim_MokSBState_name, &shim_guid, @@ -53,7 +53,7 @@ enum efi_secureboot_mode efi_get_secureb /* If it fails, we don't care why. Default to secure */ if (status != EFI_SUCCESS) goto secure_boot_enabled; - if (!(attr & EFI_VARIABLE_RUNTIME_ACCESS) && moksbstate == 1) + if (!(attr & EFI_VARIABLE_NON_VOLATILE) && moksbstate == 1) return efi_secureboot_mode_disabled;
secure_boot_enabled: