[RFC PATCH v2 4/8] clavis: Prevent clavis boot param from changing during kexec

[Eric Snowberg]

Use the new Clavis EFI RT variable to validate the clavis boot param didn't
change during a reboot. If the boot param is different or missing, use the
one stored in EFI instead. This will prevent a pivot in the root of trust
for the upcoming Clavis LSM.

Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
---
 security/clavis/Makefile         |  3 ++
 security/clavis/clavis.h         | 16 ++++++++++
 security/clavis/clavis_efi.c     | 50 ++++++++++++++++++++++++++++++++
 security/clavis/clavis_keyring.c | 17 +++++++++--
 4 files changed, 84 insertions(+), 2 deletions(-)
 create mode 100644 security/clavis/clavis.h
 create mode 100644 security/clavis/clavis_efi.c

diff --git a/security/clavis/Makefile b/security/clavis/Makefile
index 16c451f45f37..2b2b3bc8eef4 100644
--- a/security/clavis/Makefile
+++ b/security/clavis/Makefile
@@ -1,3 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_SECURITY_CLAVIS) += clavis_keyring.o
+ifeq ($(CONFIG_EFI),y)
+obj-$(CONFIG_SECURITY_CLAVIS) += clavis_efi.o
+endif
diff --git a/security/clavis/clavis.h b/security/clavis/clavis.h
new file mode 100644
index 000000000000..708dd0b1cc76
--- /dev/null
+++ b/security/clavis/clavis.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _SECURITY_CLAVIS_H_
+#define _SECURITY_CLAVIS_H_
+
+struct asymmetric_key_id;
+
+#ifdef CONFIG_EFI
+int clavis_efi_param(struct asymmetric_key_id *kid, int len);
+#else
+static inline int __init clavis_efi_param(struct asymmetric_key_id *kid, int len)
+{
+	return -EINVAL;
+}
+#endif
+
+#endif /* _SECURITY_CLAVIS_H_ */
diff --git a/security/clavis/clavis_efi.c b/security/clavis/clavis_efi.c
new file mode 100644
index 000000000000..7bc8ef03794a
--- /dev/null
+++ b/security/clavis/clavis_efi.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <keys/asymmetric-type.h>
+#include <linux/efi.h>
+#include "clavis.h"
+
+static efi_char16_t clavis_param_name[] = L"Clavis";
+static efi_guid_t clavis_guid = LINUX_EFI_CLAVIS_GUID;
+
+int __init clavis_efi_param(struct asymmetric_key_id *kid, int len)
+{
+	unsigned char buf[64];
+	unsigned long ascii_len = sizeof(buf);
+	efi_status_t error;
+	int hex_len;
+	u32 attr;
+
+	if (!efi_enabled(EFI_BOOT)) {
+		pr_info("efi_enabled(EFI_BOOT) not set");
+		return -EPERM;
+	}
+
+	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+		pr_info("%s : EFI runtime services are not enabled\n", __func__);
+		return -EPERM;
+	}
+
+	error = efi.get_variable(clavis_param_name, &clavis_guid, &attr, &ascii_len, &buf);
+
+	if (error) {
+		pr_err("Error reading clavis parm\n");
+		return -EINVAL;
+	}
+
+	if (attr & EFI_VARIABLE_NON_VOLATILE)  {
+		pr_info("Error: NV access set\n");
+		return -EINVAL;
+	} else if (ascii_len > 0) {
+		hex_len = ascii_len / 2;
+
+		if (hex_len > len) {
+			pr_info("invalid length\n");
+			return -EINVAL;
+		}
+		kid->len = hex_len;
+		return hex2bin(kid->data, buf, kid->len);
+	}
+
+	pr_info("Error: invalid size\n");
+	return -EINVAL;
+}
diff --git a/security/clavis/clavis_keyring.c b/security/clavis/clavis_keyring.c
index e92b8bd4ad5b..1225a8ee1e5a 100644
--- a/security/clavis/clavis_keyring.c
+++ b/security/clavis/clavis_keyring.c
@@ -4,6 +4,7 @@
 #include <linux/integrity.h>
 #include <keys/asymmetric-type.h>
 #include <keys/system_keyring.h>
+#include "clavis.h"
 
 static struct key *clavis_keyring;
 static struct asymmetric_key_id *setup_keyid;
@@ -82,9 +83,21 @@ static int __init clavis_keyring_init(void)
 
 void __init late_init_clavis_setup(void)
 {
-	if (!setup_keyid)
+	int error;
+	struct {
+		struct asymmetric_key_id id;
+		unsigned char data[MAX_BIN_KID];
+	} efi_keyid;
+	struct asymmetric_key_id *keyid = &efi_keyid.id;
+
+	error = clavis_efi_param(keyid, sizeof(efi_keyid.data));
+
+	if (error && !setup_keyid)
 		return;
 
+	if (error)
+		keyid = setup_keyid;
+
 	clavis_keyring_init();
-	system_key_link(clavis_keyring, setup_keyid);
+	system_key_link(clavis_keyring, keyid);
 }
-- 
2.43.0