Re: [PATCH v10 6/8] ima: kexec: move IMA log copy from kexec load to execute

[Mimi Zohar]

On Mon, 2025-03-17 at 18:04 -0700, steven chen wrote:
> ima_dump_measurement_list() is called during kexec 'load', which may
> result in loss of IMA measurements during kexec soft reboot. Due to 
> missed measurements that only occurred after kexec 'load', this function 
> needs to be called during kexec 'execute'.

-> , defer calling ima_dump_measurement_list() to 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 so that it 
>    becomes accessible both during kexec 'load' and 'execute'.
>  - Move ima_dump_measurement_list() call from ima_add_kexec_buffer()
>    to ima_update_kexec_buffer().
>  - Copy the measurement list as much as possible.

Let's summarize the above changes, as below, and then remove the list.

Define and call the new kimage_file_post_load() to call ima_kexec_post_load(),
which registers the reboot notifier (ima_update_kexec_buffer).

Finally, move ima_dump_measurement_list() from ima_add_kexec_buffer()
to ima_update_kexec_buffer() to defer copying the measurement list.

>  - 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' would corrupt the buffer.

Instead of adding and then removing the ima_reset_kexec_file() call from
ima_add_kexec_buffer(), defer adding the test in ima_alloc_kexec_file_buf() to
see if the segment size has changed.  That should be a subsequent patch, after
this one.

ima_reset_kexec_file() is then ever called from only one place.  Combine
ima_reset_kexec_file() with ima_free_kexec_file_buf().

thanks,

Mimi

> 
> Signed-off-by: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Baoquan He <bhe@xxxxxxxxxx> 
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> Cc: Dave Young <dyoung@xxxxxxxxxx>
> Signed-off-by: steven chen <chenste@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> ---
>  kernel/kexec_file.c                | 10 ++++++
>  security/integrity/ima/ima_kexec.c | 51 ++++++++++++++++++------------
>  2 files changed, 40 insertions(+), 21 deletions(-)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 606132253c79..ab449b43aaee 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -201,6 +201,13 @@ kimage_validate_signature(struct kimage *image)
>  }
>  #endif
>  
> +static void kimage_file_post_load(struct kimage *image)
> +{
> +#ifdef CONFIG_IMA_KEXEC
> +	ima_kexec_post_load(image);
> +#endif
> +}
> +
>  /*
>   * In file mode list of segments is prepared by kernel. Copy relevant
>   * data from user space, do error checking, prepare segment list
> @@ -428,6 +435,9 @@ 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 9336c4f60650..c390c745f882 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -19,6 +19,7 @@
>  #ifdef CONFIG_IMA_KEXEC
>  static bool ima_kexec_update_registered;
>  static struct seq_file ima_kexec_file;
> +static size_t kexec_segment_size;
>  static void *ima_kexec_buffer;
>  
>  static void ima_reset_kexec_file(struct seq_file *sf)
> @@ -67,7 +68,7 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
>   *    if the size of the allocated memory is not less than the size of IMA measurement list
>   *        copy the measurement list to the allocated memory.
>   *    else
> - *        return error
> + *        copy the measurement list as much as possible.
>   */
>  static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>  				     unsigned long segment_size)
> @@ -95,9 +96,6 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>  		}
>  	}
>  
> -	if (ret < 0)
> -		goto out;
> -
>  	/*
>  	 * fill in reserved space with some buffer details
>  	 * (eg. version, buffer size, number of measurements)
> @@ -117,7 +115,7 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>  
>  	*buffer_size = ima_kexec_file.count;
>  	*buffer = ima_kexec_file.buf;
> -out:
> +
>  	return ret;
>  }
>  
> @@ -135,9 +133,8 @@ void ima_add_kexec_buffer(struct kimage *image)
>  	unsigned long binary_runtime_size;
>  
>  	/* use more understandable variable names than defined in kbuf */
> +	size_t kexec_buffer_size = 0;
>  	void *kexec_buffer = NULL;
> -	size_t kexec_buffer_size;
> -	size_t kexec_segment_size;
>  	int ret;
>  
>  	/*
> @@ -162,13 +159,6 @@ void ima_add_kexec_buffer(struct kimage *image)
>  		return;
>  	}
>  
> -	ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
> -				  kexec_segment_size);
> -	if (!kexec_buffer) {
> -		pr_err("Not enough memory for the kexec measurement buffer.\n");
> -		return;
> -	}
> -
>  	kbuf.buffer = kexec_buffer;
>  	kbuf.bufsz = kexec_buffer_size;
>  	kbuf.memsz = kexec_segment_size;
> @@ -186,12 +176,6 @@ 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);
>  }
> @@ -202,7 +186,32 @@ 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;
> +	size_t buf_size = 0;
> +	int ret = NOTIFY_OK;
> +	void *buf = NULL;
> +
> +	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;
>  }
>  
>  static struct notifier_block update_buffer_nb = {