[PATCH v6 1/7] ima: define and call ima_alloc_kexec_file_buf

steven chen
2025-01-24T22:43:55Z

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'.

This patch includes the following changes:
- Refactor ima_dump_measurement_list() to move the memory allocation
to a separate function ima_alloc_kexec_file_buf() which allocates
buffer of size 'kexec_segment_size' at kexec 'load'.
- Make the local variable ima_kexec_file in ima_dump_measurement_list()
a local static to the file, so that it can be accessed from
ima_alloc_kexec_file_buf(). Compare actual memory required to ensure
there is enough memory for the entire measurement record.
- Copy as many measurement events as possible.
- Make necessary changes to the function ima_add_kexec_buffer() to call
the above two functions.
- Compared the memory size allocated with memory size of the entire
measurement record. If there is not enough memory, it will copy as many
IMA measurement records as possible, and this situation will result
in a failure of remote attestation.

Author: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Signed-off-by: steven chen <chenste@linux.microsoft.com>
---
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_kexec.c | 105 +++++++++++++++++++++--------
security/integrity/ima/ima_queue.c | 4 +-
3 files changed, 80 insertions(+), 30 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 3c323ca213d4..447a6eb07c2d 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -274,6 +274,7 @@ bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
int ima_restore_measurement_entry(struct ima_template_entry *entry);
int ima_restore_measurement_list(loff_t bufsize, void *buf);
int ima_measurements_show(struct seq_file *m, void *v);
+int ima_get_binary_runtime_entry_size(struct ima_template_entry *entry);
unsigned long ima_get_binary_runtime_size(void);
int ima_init_template(void);
void ima_init_template_list(void);
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 52e00332defe..b60a902460e2 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -15,62 +15,99 @@
#include "ima.h"

#ifdef CONFIG_IMA_KEXEC
+static struct seq_file ima_kexec_file;
+
+static void ima_reset_kexec_file(struct seq_file *sf)
+{
+ sf->buf = NULL;
+ sf->size = 0;
+ sf->read_pos = 0;
+ sf->count = 0;
+}
+
+static void ima_free_kexec_file_buf(struct seq_file *sf)
+{
+ vfree(sf->buf);
+ ima_reset_kexec_file(sf);
+}
+
+static int ima_alloc_kexec_file_buf(size_t segment_size)
+{
+ /*
+ * kexec 'load' may be called multiple times.
+ * Free and realloc the buffer only if the segment_size is
+ * changed from the previous kexec 'load' call.
+ */
+ if (ima_kexec_file.buf &&
+ (ima_kexec_file.size == segment_size)) {
+ goto out;
+ }
+
+ 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;
+
+out:
+ 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 ima_queue_entry *qe;
- struct seq_file file;
struct ima_kexec_hdr khdr;
int ret = 0;
+ size_t entry_size = 0;

- /* segment size can't change between kexec load and execute */
- file.buf = vmalloc(segment_size);
- if (!file.buf) {
- ret = -ENOMEM;
- goto out;
+ if (!ima_kexec_file.buf) {
+ pr_err("Kexec file buf not allocated\n");
+ return -EINVAL;
}

- file.file = NULL;
- file.size = segment_size;
- file.read_pos = 0;
- file.count = sizeof(khdr); /* reserved space */
-
memset(&khdr, 0, sizeof(khdr));
khdr.version = 1;
+
+ /* Copy as many IMA measurements list records as possible */
list_for_each_entry_rcu(qe, &ima_measurements, later) {
- if (file.count < file.size) {
+ entry_size += ima_get_binary_runtime_entry_size(qe->entry);
+ if (entry_size <= segment_size) {
khdr.count++;
- ima_measurements_show(&file, qe);
+ ima_measurements_show(&ima_kexec_file, qe);
} else {
ret = -EINVAL;
+ pr_err("IMA log file is too big for Kexec buf\n");
break;
}
}

- if (ret < 0)
- goto out;
-
/*
* fill in reserved space with some buffer details
* (eg. version, buffer size, number of measurements)
*/
- khdr.buffer_size = file.count;
+ khdr.buffer_size = ima_kexec_file.count;
if (ima_canonical_fmt) {
khdr.version = cpu_to_le16(khdr.version);
khdr.count = cpu_to_le64(khdr.count);
khdr.buffer_size = cpu_to_le64(khdr.buffer_size);
}
- memcpy(file.buf, &khdr, sizeof(khdr));
+ memcpy(ima_kexec_file.buf, &khdr, sizeof(khdr));

print_hex_dump_debug("ima dump: ", DUMP_PREFIX_NONE, 16, 1,
- file.buf, file.count < 100 ? file.count : 100,
+ ima_kexec_file.buf, ima_kexec_file.count < 100 ?
+ ima_kexec_file.count : 100,
true);

- *buffer_size = file.count;
- *buffer = file.buf;
-out:
- if (ret == -EINVAL)
- vfree(file.buf);
+ *buffer_size = ima_kexec_file.count;
+ *buffer = ima_kexec_file.buf;
+
return ret;
}

@@ -89,7 +126,7 @@ void ima_add_kexec_buffer(struct kimage *image)

/* use more understandable variable names than defined in kbuf */
void *kexec_buffer = NULL;
- size_t kexec_buffer_size;
+ size_t kexec_buffer_size = 0;
size_t kexec_segment_size;
int ret;

@@ -109,13 +146,19 @@ void ima_add_kexec_buffer(struct kimage *image)
return;
}

- ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
- kexec_segment_size);
- if (!kexec_buffer) {
+ ret = ima_alloc_kexec_file_buf(kexec_segment_size);
+ if (ret < 0) {
pr_err("Not enough memory for the kexec measurement buffer.\n");
return;
}

+ ret = ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
+ kexec_segment_size);
+ if (ret < 0) {
+ pr_err("Failed to dump IMA measurements. Error:%d.\n", ret);
+ return;
+ }
+
kbuf.buffer = kexec_buffer;
kbuf.bufsz = kexec_buffer_size;
kbuf.memsz = kexec_segment_size;
@@ -130,6 +173,12 @@ void ima_add_kexec_buffer(struct kimage *image)
image->ima_buffer_size = kexec_segment_size;
image->ima_buffer = kexec_buffer;

+ /*
+ * kexec owns kexec_buffer after kexec_add_buffer() is called
+ * and it will vfree() that buffer.
+ */
+ ima_reset_kexec_file(&ima_kexec_file);
+
kexec_dprintk("kexec measurement buffer for the loaded kernel at 0x%lx.\n",
kbuf.mem);
}
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 532da87ce519..a3559bae251f 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -71,7 +71,7 @@ static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
* binary_runtime_measurement list entry, which contains a
* couple of variable length fields (e.g template name and data).
*/
-static int get_binary_runtime_size(struct ima_template_entry *entry)
+int ima_get_binary_runtime_entry_size(struct ima_template_entry *entry)
{
int size = 0;

@@ -115,7 +115,7 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
if (binary_runtime_size != ULONG_MAX) {
int size;

- size = get_binary_runtime_size(entry);
+ size = ima_get_binary_runtime_entry_size(entry);
binary_runtime_size = (binary_runtime_size < ULONG_MAX - size) ?
binary_runtime_size + size : ULONG_MAX;
}
--
2.25.1