ima: define and call ima_alloc_kexec_file_buf()

JIRA: https://issues.redhat.com/browse/RHEL-114162

Upstream Status: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit c95e1ac
Author: Steven Chen <chenste@linux.microsoft.com>
Date:   Mon Apr 21 15:25:08 2025 -0700

    ima: define and call ima_alloc_kexec_file_buf()

    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

    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'.

    After moving the vfree() here at this stage in the patch set, the IMA
    measurement list fails to verify when doing two consecutive "kexec -s -l"
    with/without a "kexec -s -u" in between.  Only after "ima: kexec: move
    IMA log copy from kexec load to execute" the IMA measurement list verifies
    properly with the vfree() here.

    Co-developed-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
    Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
    Signed-off-by: Steven Chen <chenste@linux.microsoft.com>
    Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
    Acked-by: Baoquan He <bhe@redhat.com>
    Tested-by: Stefan Berger <stefanb@linux.ibm.com> # ppc64/kvm
    Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Signed-off-by: Baoquan He <bhe@redhat.com>

Author: Baoquan He

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) {