[PATCH v5 4/8] ima: kexec: define functions to copy IMA log at soft boot

[Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>]

IMA log is copied to the new Kernel during kexec 'load' using 
ima_dump_measurement_list().  The log copy at kexec 'load' may result in
loss of IMA measurements during kexec soft reboot.  It needs to be copied
over during kexec 'execute'.  Setup the needed infrastructure to move the
IMA log copy from kexec 'load' to 'execute'. 

Define a new IMA hook ima_update_kexec_buffer() as a stub function.
It will be used to call ima_dump_measurement_list() during kexec 
'execute'.   

Implement kimage_file_post_load() and ima_kexec_post_load() functions
to be invoked after the new Kernel image has been loaded for kexec.
ima_kexec_post_load() maps the IMA buffer to a segment in the newly
loaded Kernel.  It also registers the reboot notifier_block to trigger
ima_update_kexec_buffer() at exec 'execute'.

Signed-off-by: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/ima.h                |  3 ++
 kernel/kexec_file.c                |  5 ++++
 security/integrity/ima/ima_kexec.c | 46 ++++++++++++++++++++++++++++++
 3 files changed, 54 insertions(+)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 86b57757c7b1..006db20f852d 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -49,6 +49,9 @@ static inline void ima_appraise_parse_cmdline(void) {}
 
 #ifdef CONFIG_IMA_KEXEC
 extern void ima_add_kexec_buffer(struct kimage *image);
+extern void ima_kexec_post_load(struct kimage *image);
+#else
+static inline void ima_kexec_post_load(struct kimage *image) {}
 #endif
 
 #else
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 0e3689bfb0bb..fe59cb7c179d 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -186,6 +186,11 @@ kimage_validate_signature(struct kimage *image)
 }
 #endif
 
+void kimage_file_post_load(struct kimage *image)
+{
+	ima_kexec_post_load(image);
+}
+
 /*
  * In file mode list of segments is prepared by kernel. Copy relevant
  * data from user space, do error checking, prepare segment list
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index ccb072617c2d..1d4d6c122d82 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -12,10 +12,14 @@
 #include <linux/kexec.h>
 #include <linux/of.h>
 #include <linux/ima.h>
+#include <linux/reboot.h>
+#include <asm/page.h>
 #include "ima.h"
 
 #ifdef CONFIG_IMA_KEXEC
 static struct seq_file ima_kexec_file;
+static void *ima_kexec_buffer;
+static bool ima_kexec_update_registered;
 
 static void ima_reset_kexec_file(struct seq_file *sf)
 {
@@ -184,6 +188,48 @@ void ima_add_kexec_buffer(struct kimage *image)
 	kexec_dprintk("kexec measurement buffer for the loaded kernel at 0x%lx.\n",
 		      kbuf.mem);
 }
+
+/*
+ * Called during kexec execute so that IMA can update the measurement list.
+ */
+static int ima_update_kexec_buffer(struct notifier_block *self,
+				   unsigned long action, void *data)
+{
+	return NOTIFY_OK;
+}
+
+struct notifier_block update_buffer_nb = {
+	.notifier_call = ima_update_kexec_buffer,
+};
+
+/*
+ * Create a mapping for the source pages that contain the IMA buffer
+ * so we can update it later.
+ */
+void ima_kexec_post_load(struct kimage *image)
+{
+	if (ima_kexec_buffer) {
+		kimage_unmap_segment(ima_kexec_buffer);
+		ima_kexec_buffer = NULL;
+	}
+
+	if (!image->ima_buffer_addr)
+		return;
+
+	ima_kexec_buffer = kimage_map_segment(image,
+					      image->ima_buffer_addr,
+					      image->ima_buffer_size);
+	if (!ima_kexec_buffer) {
+		pr_err("%s: Could not map measurements buffer.\n", __func__);
+		return;
+	}
+
+	if (!ima_kexec_update_registered) {
+		register_reboot_notifier(&update_buffer_nb);
+		ima_kexec_update_registered = true;
+	}
+}
+
 #endif /* IMA_KEXEC */
 
 /*
-- 
2.25.1