[PATCH v4 3/8] ima: based on policy require signed kexec kernel images

Mimi Zohar
2018-05-29T18:04:23Z

The original kexec_load syscall can not verify file signatures, nor can
the kexec image be measured. Based on policy, deny the kexec_load
syscall.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Luis R. Rodriguez <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: David Howells <dhowells@redhat.com>

Changelog v3:
- use switch/case
---
include/linux/ima.h | 7 +++++++
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_main.c | 27 +++++++++++++++++++++++++++
security/integrity/ima/ima_policy.c | 2 ++
security/security.c | 7 ++++++-
5 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 0e4647e0eb60..84806b54b50a 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -11,6 +11,7 @@
#define _LINUX_IMA_H

#include <linux/fs.h>
+#include <linux/security.h>
#include <linux/kexec.h>
struct linux_binprm;

@@ -19,6 +20,7 @@ extern int ima_bprm_check(struct linux_binprm *bprm);
extern int ima_file_check(struct file *file, int mask, int opened);
extern void ima_file_free(struct file *file);
extern int ima_file_mmap(struct file *file, unsigned long prot);
+extern int ima_load_data(enum kernel_load_data_id id);
extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
enum kernel_read_file_id id);
@@ -49,6 +51,11 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)
return 0;
}

+static inline int ima_load_data(enum kernel_load_data_id id)
+{
+ return 0;
+}
+
static inline int ima_read_file(struct file *file, enum kernel_read_file_id id)
{
return 0;
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 354bb5716ce3..78c15264b17b 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -232,6 +232,7 @@ int ima_policy_show(struct seq_file *m, void *v);
#define IMA_APPRAISE_MODULES 0x08
#define IMA_APPRAISE_FIRMWARE 0x10
#define IMA_APPRAISE_POLICY 0x20
+#define IMA_APPRAISE_KEXEC 0x40

#ifdef CONFIG_IMA_APPRAISE
int ima_appraise_measurement(enum ima_hooks func,
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 83f84928ad76..a565d46084c2 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -499,6 +499,33 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
MAY_READ, func, 0);
}

+/**
+ * ima_load_data - appraise decision based on policy
+ * @id: kernel load data caller identifier
+ *
+ * Callers of this LSM hook can not measure, appraise, or audit the
+ * data provided by userspace. Enforce policy rules requring a file
+ * signature (eg. kexec'ed kernel image).
+ *
+ * For permission return 0, otherwise return -EACCES.
+ */
+int ima_load_data(enum kernel_load_data_id id)
+{
+ if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
+ return 0;
+
+ switch (id) {
+ case LOADING_KEXEC_IMAGE:
+ if (ima_appraise & IMA_APPRAISE_KEXEC) {
+ pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
+ return -EACCES; /* INTEGRITY_UNKNOWN */
+ }
+ default:
+ break;
+ }
+ return 0;
+}
+
static int __init init_ima(void)
{
int error;
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 8bbc18eb07eb..c27f6993b07a 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -448,6 +448,8 @@ static int ima_appraise_flag(enum ima_hooks func)
return IMA_APPRAISE_FIRMWARE;
else if (func == POLICY_CHECK)
return IMA_APPRAISE_POLICY;
+ else if (func == KEXEC_KERNEL_CHECK)
+ return IMA_APPRAISE_KEXEC;
return 0;
}

diff --git a/security/security.c b/security/security.c
index c2de2f134854..4927e7cc7d96 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1058,7 +1058,12 @@ EXPORT_SYMBOL_GPL(security_kernel_post_read_file);

int security_kernel_load_data(enum kernel_load_data_id id)
{
- return call_int_hook(kernel_load_data, 0, id);
+ int ret;
+
+ ret = call_int_hook(kernel_load_data, 0, id);
+ if (ret)
+ return ret;
+ return ima_load_data(id);
}

int security_task_fix_setuid(struct cred *new, const struct cred *old,
--
2.7.5