Re: [PATCH v5 5/8] ima: kexec: move IMA log copy from kexec load to execute

[Stefan Berger <stefanb@linux.ibm.com>]

On 2/14/24 10:38, Tushar Sugandhi wrote:
> 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:
>   - 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.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> ---
>   kernel/kexec_file.c                |  3 ++
>   security/integrity/ima/ima_kexec.c | 45 +++++++++++++++++++-----------
>   2 files changed, 32 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index fe59cb7c179d..2d5df320c34f 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -410,6 +410,9 @@ 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 1d4d6c122d82..98fc9b9782a2 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)
> @@ -129,7 +130,6 @@ 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;
> -	size_t kexec_segment_size;
>   	int ret;
>   
>   	/*
> @@ -154,14 +154,6 @@ 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("%s: Failed to dump IMA measurements. Error:%d.\n",
> -		       __func__, ret);
> -		return;
> -	}
> -
>   	kbuf.buffer = kexec_buffer;
>   	kbuf.bufsz = kexec_buffer_size;
>   	kbuf.memsz = kexec_segment_size;
> @@ -179,12 +171,6 @@ 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);
>   }
> @@ -195,7 +181,34 @@ 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;
> +	int ret = NOTIFY_OK;
> +
> +	if (!kexec_in_progress) {
> +		pr_info("%s: No kexec in progress.\n", __func__);
> +		return ret;
> +	}
> +
> +	if (!ima_kexec_buffer) {
> +		pr_err("%s: Kexec buffer not set.\n", __func__);
> +		return ret;
> +	}
> +
> +	ret = ima_dump_measurement_list(&buf_size, &buf,
> +					kexec_segment_size);
> +
> +	if (!buf) {

Use 'if (ret)' ? You're setting *buffer = NULL in case of error but ret 
should be used to test for failure.

> +		pr_err("%s: Dump measurements failed. Error:%d\n",
> +		       __func__, ret);
> +		goto out;
> +	}
> +	memcpy(ima_kexec_buffer, buf, buf_size);
> +out:
> +	kimage_unmap_segment(ima_kexec_buffer);
> +	ima_kexec_buffer = NULL;
> +
> +	return ret;
>   }
>   
>   struct notifier_block update_buffer_nb = {