[PATCH 02/10] ima: implement function to populate buffer at kexec execute

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

There is no existing IMA functionality to just populate the buffer at
kexec execute with IMA measurements.

Implement a function to iterate over ima_measurements and populate the
ima_kexec_file buffer.  After the loop, populate ima_khdr with buffer
details (version, buffer size, number of measurements).  Copy the ima_khdr
data into ima_kexec_file.buf and update buffer_size and buffer.

The patch assumes that the ima_kexec_file.size is sufficient to hold all
the measurements.  It returns an error and does not handle scenarios where
additional space might be needed.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
---
 security/integrity/ima/ima_kexec.c | 52 ++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 48a683874044..858b67689701 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -62,6 +62,58 @@ static int ima_allocate_buf_at_kexec_load(void)
 	return 0;
 }
 
+static int ima_populate_buf_at_kexec_execute(unsigned long *buffer_size, void **buffer)
+{
+	struct ima_queue_entry *qe;
+	int ret = 0;
+
+	/*
+	 * Ensure the kexec buffer is large enough to hold ima_khdr
+	 */
+	if (ima_kexec_file.size < sizeof(ima_khdr)) {
+		pr_err("%s: Kexec buffer size too low to hold ima_khdr\n",
+			__func__);
+		ima_clear_kexec_file();
+		return -ENOMEM;
+	}
+
+	list_for_each_entry_rcu(qe, &ima_measurements, later) {
+		if (ima_kexec_file.count < ima_kexec_file.size) {
+			ima_khdr.count++;
+			ima_measurements_show(&ima_kexec_file, qe);
+		} else {
+			ret = -ENOMEM;
+			pr_err("%s: Kexec ima_measurements buffer too small\n",
+				__func__);
+			break;
+		}
+	}
+	if (ret < 0)
+		goto out;
+
+	/*
+	 * fill in reserved space with some buffer details
+	 * (eg. version, buffer size, number of measurements)
+	 */
+	ima_khdr.buffer_size = ima_kexec_file.count;
+	if (ima_canonical_fmt) {
+		ima_khdr.version = cpu_to_le16(ima_khdr.version);
+		ima_khdr.count = cpu_to_le64(ima_khdr.count);
+		ima_khdr.buffer_size = cpu_to_le64(ima_khdr.buffer_size);
+	}
+
+	memcpy(ima_kexec_file.buf, &ima_khdr, sizeof(ima_khdr));
+	*buffer_size = ima_kexec_file.count;
+	*buffer = ima_kexec_file.buf;
+
+out:
+	if (ret < 0)
+		ima_clear_kexec_file();
+
+	return ret;
+}
+
+
 static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
 				     unsigned long segment_size)
 {
-- 
2.25.1