[PATCH 01/10] ima: implement function to allocate buffer at kexec load

[Tushar Sugandhi <tusharsu@linux.microsoft.com>]

IMA does not provide a mechanism to allocate memory for IMA log storage
during kexec operation.  The function should handle the scenario where
the kexec load is called multiple times. 

Implement a function to allocate buffer of size kexec_segment_size at
kexec load.  If the buffer was already allocated, free that buffer and
reallocate.  Finally, initialize ima_khdr struct. 

The patch operates under the assumption that the segment size does not
change between kexec load and execute.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
---
 security/integrity/ima/ima_kexec.c | 47 ++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 419dc405c831..48a683874044 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -15,6 +15,53 @@
 #include "ima.h"
 
 #ifdef CONFIG_IMA_KEXEC
+struct seq_file ima_kexec_file;
+struct ima_kexec_hdr ima_khdr;
+static size_t kexec_segment_size;
+
+void ima_clear_kexec_file(void)
+{
+	vfree(ima_kexec_file.buf);
+	ima_kexec_file.buf = NULL;
+	ima_kexec_file.size = 0;
+	ima_kexec_file.read_pos = 0;
+	ima_kexec_file.count = 0;
+}
+
+static int ima_allocate_buf_at_kexec_load(void)
+{
+	if ((kexec_segment_size == 0) ||
+	    (kexec_segment_size == ULONG_MAX) ||
+	    ((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {
+		pr_err("%s: Invalid segment size for kexec: %zu\n",
+			__func__, kexec_segment_size);
+		return -EINVAL;
+	}
+
+	/* if kexec load was called before, clear the existing buffer
+	 *  before allocating a new one
+	 */
+	if (ima_kexec_file.buf)
+		ima_clear_kexec_file();
+
+	/* segment size can't change between kexec load and execute */
+	ima_kexec_file.buf = vmalloc(kexec_segment_size);
+	if (!ima_kexec_file.buf) {
+		pr_err("%s: No memory for ima kexec measurement buffer\n",
+			__func__);
+		return -ENOMEM;
+	}
+
+	ima_kexec_file.size = kexec_segment_size;
+	ima_kexec_file.read_pos = 0;
+	ima_kexec_file.count = sizeof(ima_khdr);	/* reserved space */
+
+	memset(&ima_khdr, 0, sizeof(ima_khdr));
+	ima_khdr.version = 1;
+
+	return 0;
+}
+
 static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
 				     unsigned long segment_size)
 {
-- 
2.25.1