[09/18] Secure boot: Add a dummy kernel parameter that will switch on Secure Boot mode

Commit Message

Chun-Yi Lee Aug. 22, 2013, 11:01 a.m. UTC

From: Josh Boyer <[e-mail]>

This forcibly drops CAP_COMPROMISE_KERNEL from both cap_permitted and cap_bset
in the init_cred struct, which everything else inherits from.  This works on
any machine and can be used to develop even if the box doesn't have UEFI.

Signed-off-by: Josh Boyer <[e-mail]>
Acked-by: Lee, Chun-Yi <[e-mail]>
Signed-off-by: Lee, Chun-Yi <[e-mail]>
---
 Documentation/kernel-parameters.txt |    7 +++++++
 kernel/cred.c                       |   17 +++++++++++++++++
 2 files changed, 24 insertions(+), 0 deletions(-)

Comments

Pavel Machek Aug. 25, 2013, 4:16 p.m. UTC | #1

You may want to check subject. If it does something, it is not dummy.

> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2784,6 +2784,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			Note: increases power consumption, thus should only be
>  			enabled if running jitter sensitive (HPC/RT) workloads.
>  
> +	secureboot_enable=
> +			[KNL] Enables an emulated UEFI Secure Boot mode.  This
> +			locks down various aspects of the kernel guarded by the
> +			CAP_COMPROMISE_KERNEL capability.  This includes things
> +			like /dev/mem, IO port access, and other areas.  It can
> +			be used on non-UEFI machines for testing purposes.
> +
>  	security=	[SECURITY] Choose a security module to enable at boot.
>  			If this boot parameter is not specified, only the first
>  			security module asking for security registration will be
> diff --git a/kernel/cred.c b/kernel/cred.c
> index e0573a4..c3f4e3e 100644
> --- a/kernel/cred.c
> +++ b/kernel/cred.c
> @@ -565,6 +565,23 @@ void __init cred_init(void)
>  				     0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
>  }
>  
> +void __init secureboot_enable()
> +{
> +	pr_info("Secure boot enabled\n");
> +	cap_lower((&init_cred)->cap_bset, CAP_COMPROMISE_KERNEL);
> +	cap_lower((&init_cred)->cap_permitted, CAP_COMPROMISE_KERNEL);
> +}

OTOH you don't implement CAP_COMPROMISE_KERNEL, so it is dummy after
all. But CAP_COMPROMISE_KERNEL is infeasible to implement, right?
									Pavel

Patch

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 15356ac..6ad8292 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2784,6 +2784,13 @@  bytes respectively. Such letter suffixes can also be entirely omitted.
 			Note: increases power consumption, thus should only be
 			enabled if running jitter sensitive (HPC/RT) workloads.
 
+	secureboot_enable=
+			[KNL] Enables an emulated UEFI Secure Boot mode.  This
+			locks down various aspects of the kernel guarded by the
+			CAP_COMPROMISE_KERNEL capability.  This includes things
+			like /dev/mem, IO port access, and other areas.  It can
+			be used on non-UEFI machines for testing purposes.
+
 	security=	[SECURITY] Choose a security module to enable at boot.
 			If this boot parameter is not specified, only the first
 			security module asking for security registration will be
diff --git a/kernel/cred.c b/kernel/cred.c
index e0573a4..c3f4e3e 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -565,6 +565,23 @@  void __init cred_init(void)
 				     0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 }
 
+void __init secureboot_enable()
+{
+	pr_info("Secure boot enabled\n");
+	cap_lower((&init_cred)->cap_bset, CAP_COMPROMISE_KERNEL);
+	cap_lower((&init_cred)->cap_permitted, CAP_COMPROMISE_KERNEL);
+}
+
+/* Dummy Secure Boot enable option to fake out UEFI SB=1 */
+static int __init secureboot_enable_opt(char *str)
+{
+	int sb_enable = !!simple_strtol(str, NULL, 0);
+	if (sb_enable)
+		secureboot_enable();
+	return 1;
+}
+__setup("secureboot_enable=", secureboot_enable_opt);
+
 /**
  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
  * @daemon: A userspace daemon to be used as a reference