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

Eric Snowberg
2024-03-11T16:19:45Z

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@oracle.com>
---
security/clavis/Makefile | 3 ++
security/clavis/clavis.h | 12 ++++++++
security/clavis/clavis_efi.c | 50 ++++++++++++++++++++++++++++++++
security/clavis/clavis_keyring.c | 17 +++++++++--
4 files changed, 80 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 ff19c1e240fd..c008cb74c762 100644
--- a/security/clavis/Makefile
+++ b/security/clavis/Makefile
@@ -1,3 +1,6 @@
# SPDX-License-Identifier: GPL-2.0

obj-$(CONFIG_SECURITY_CLAVIS_KEYRING) += clavis_keyring.o
+ifeq ($(CONFIG_EFI),y)
+obj-$(CONFIG_SECURITY_CLAVIS_KEYRING) += clavis_efi.o
+endif
diff --git a/security/clavis/clavis.h b/security/clavis/clavis.h
new file mode 100644
index 000000000000..3883c390b9e4
--- /dev/null
+++ b/security/clavis/clavis.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+struct asymmetric_key_id;
+
+#ifdef CONFIG_EFI
+int __init 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
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 9f1aede81992..c5606ed101f6 100644
--- a/security/clavis/clavis_keyring.c
+++ b/security/clavis/clavis_keyring.c
@@ -3,6 +3,7 @@
#include <linux/security.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);
}
--
2.39.3