[PATCH v11 2/9] ima: define and call ima_alloc_kexec_file_buf()

[steven chen <chenste@linux.microsoft.com>]

In the current implementation, the ima_dump_measurement_list() API is 
called during the kexec "load" phase, where a buffer is allocated and 
the measurement records are copied. Due to this, new events added after
kexec load but before kexec execute are not carried over to the new kernel
during kexec operation

To allow the buffer allocation and population to be separated into distinct
steps, make the function local seq_file "ima_kexec_file" to a file variable.

Carrying the IMA measurement list across kexec requires allocating a
buffer and copying the measurement records.  Separate allocating the
buffer and copying the measurement records into separate functions in
order to allocate the buffer at kexec 'load' and copy the measurements
at kexec 'execute'.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Signed-off-by: steven chen <chenste@linux.microsoft.com>
---
 security/integrity/ima/ima_kexec.c | 46 +++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 650beb74346c..b12ac3619b8f 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -15,26 +15,46 @@
 #include "ima.h"
 
 #ifdef CONFIG_IMA_KEXEC
+static struct seq_file ima_kexec_file;
+
+static void ima_free_kexec_file_buf(struct seq_file *sf)
+{
+	vfree(sf->buf);
+	sf->buf = NULL;
+	sf->size = 0;
+	sf->read_pos = 0;
+	sf->count = 0;
+}
+
+static int ima_alloc_kexec_file_buf(size_t segment_size)
+{
+	ima_free_kexec_file_buf(&ima_kexec_file);
+
+	/* segment size can't change between kexec load and execute */
+	ima_kexec_file.buf = vmalloc(segment_size);
+	if (!ima_kexec_file.buf)
+		return -ENOMEM;
+
+	ima_kexec_file.size = segment_size;
+	ima_kexec_file.read_pos = 0;
+	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved space */
+
+	return 0;
+}
+
 static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
 				     unsigned long segment_size)
 {
-	struct seq_file ima_kexec_file;
 	struct ima_queue_entry *qe;
 	struct ima_kexec_hdr khdr;
 	int ret = 0;
 
 	/* segment size can't change between kexec load and execute */
-	ima_kexec_file.buf = vmalloc(segment_size);
 	if (!ima_kexec_file.buf) {
-		ret = -ENOMEM;
-		goto out;
+		pr_err("Kexec file buf not allocated\n");
+		return -EINVAL;
 	}
 
-	ima_kexec_file.file = NULL;
-	ima_kexec_file.size = segment_size;
-	ima_kexec_file.read_pos = 0;
-	ima_kexec_file.count = sizeof(khdr);	/* reserved space */
-
 	memset(&khdr, 0, sizeof(khdr));
 	khdr.version = 1;
 	/* This is an append-only list, no need to hold the RCU read lock */
@@ -71,8 +91,6 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
 	*buffer_size = ima_kexec_file.count;
 	*buffer = ima_kexec_file.buf;
 out:
-	if (ret == -EINVAL)
-		vfree(ima_kexec_file.buf);
 	return ret;
 }
 
@@ -111,6 +129,12 @@ void ima_add_kexec_buffer(struct kimage *image)
 		return;
 	}
 
+	ret = ima_alloc_kexec_file_buf(kexec_segment_size);
+	if (ret < 0) {
+		pr_err("Not enough memory for the kexec measurement buffer.\n");
+		return;
+	}
+
 	ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
 				  kexec_segment_size);
 	if (!kexec_buffer) {
-- 
2.25.1