ima: based on policy require signed kexec kernel images

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: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

4 files changed, 36 insertions, 1 deletions

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 dca44cf7838e..71fecfef0939 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -496,6 +496,33 @@ 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 cdcc9a7b4e24..d5b4958decc5 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,