[PATCH v6 5/7] ima: kexec: move IMA log copy from kexec load to execute

steven chen
2025-01-24T22:55:58Z

ima_dump_measurement_list() is called during kexec 'load', which may
result in loss of IMA measurements during kexec soft reboot. It needs
to be called during kexec 'execute'.

This patch includes the following changes:
- Implement kimage_file_post_load() function to be invoked after the new
Kernel image has been loaded for kexec.
- Call kimage_file_post_load() from kexec_file_load() syscall only for
kexec soft reboot scenarios and not for KEXEC_FILE_ON_CRASH. It will
map the IMA segment, and register reboot notifier for the function
ima_update_kexec_buffer() which would copy the IMA log at kexec soft
reboot.
- Make kexec_segment_size variable local static to the file, for it to be
accessible both during kexec 'load' and 'execute'.
- Move ima_dump_measurement_list() call from ima_add_kexec_buffer()
to ima_update_kexec_buffer().
- Remove ima_reset_kexec_file() call from ima_add_kexec_buffer(), now
that the buffer is being copied at kexec 'execute', and resetting the
file at kexec 'load' will corrupt the buffer.

Author: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Reviewed-by: Tyler Hicks <code@tyhicks.com>
Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Signed-off-by: steven chen <chenste@linux.microsoft.com>
---
kernel/kexec_file.c | 8 ++++++
security/integrity/ima/ima_kexec.c | 43 +++++++++++++++++++-----------
2 files changed, 36 insertions(+), 15 deletions(-)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 4ff3ba0f3e8e..d05ce3ee2e53 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -186,6 +186,11 @@ kimage_validate_signature(struct kimage *image)
}
#endif

+static void kimage_file_post_load(struct kimage *image)
+{
+ ima_kexec_post_load(image);
+}
+
/*
* In file mode list of segments is prepared by kernel. Copy relevant
* data from user space, do error checking, prepare segment list
@@ -413,6 +418,9 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,

kimage_terminate(image);

+ if (!(flags & KEXEC_FILE_ON_CRASH))
+ kimage_file_post_load(image);
+
ret = machine_kexec_post_load(image);
if (ret)
goto out;
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 854b90d34e2d..d5f004cfeaec 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -19,6 +19,7 @@
#ifdef CONFIG_IMA_KEXEC
static struct seq_file ima_kexec_file;
static void *ima_kexec_buffer;
+static size_t kexec_segment_size;
static bool ima_kexec_update_registered;

static void ima_reset_kexec_file(struct seq_file *sf)
@@ -131,7 +132,6 @@ 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 = 0;
- size_t kexec_segment_size;
int ret;

/*
@@ -156,13 +156,6 @@ void ima_add_kexec_buffer(struct kimage *image)
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;
@@ -180,12 +173,6 @@ void ima_add_kexec_buffer(struct kimage *image)
image->ima_segment_index = image->nr_segments - 1;
image->is_ima_segment_index_set = true;

- /*
- * 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);
}
@@ -196,7 +183,33 @@ void ima_add_kexec_buffer(struct kimage *image)
static int ima_update_kexec_buffer(struct notifier_block *self,
unsigned long action, void *data)
{
- return NOTIFY_OK;
+ void *buf = NULL;
+ size_t buf_size = 0;
+ int ret = NOTIFY_OK;
+
+ if (!kexec_in_progress) {
+ pr_info("No kexec in progress.\n");
+ return ret;
+ }
+
+ if (!ima_kexec_buffer) {
+ pr_err("Kexec buffer not set.\n");
+ return ret;
+ }
+
+ ret = ima_dump_measurement_list(&buf_size, &buf,
+ kexec_segment_size);
+
+ if (ret)
+ pr_err("Dump measurements failed. Error:%d\n", ret);
+
+ if (buf_size != 0)
+ memcpy(ima_kexec_buffer, buf, buf_size);
+
+ kimage_unmap_segment(ima_kexec_buffer);
+ ima_kexec_buffer = NULL;
+
+ return ret;
}

struct notifier_block update_buffer_nb = {
--
2.25.1