Re: [PATCH v13 5/9] ima: kexec: define functions to copy IMA log at soft boot

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

On 4/21/25 6:25 PM, steven chen wrote:
> From: Steven Chen <chenste@linux.microsoft.com>
> 
> The IMA log is currently copied to the new kernel during kexec 'load'
> using ima_dump_measurement_list(). However, the log copied at kexec
> 'load' may result in loss of IMA measurements that only occurred after
> kexec "load'. Setup the needed infrastructure to move the IMA log copy
> from kexec 'load' to 'execute'.
> 
> Define a new IMA hook ima_update_kexec_buffer() as a stub function.
> It will be used to call ima_dump_measurement_list() during kexec 'execute'.
> 
> Implement ima_kexec_post_load() function to be invoked after the new
> Kernel image has been loaded for kexec. ima_kexec_post_load() maps the
> IMA buffer to a segment in the newly loaded Kernel.  It also registers
> the reboot notifier_block to trigger ima_update_kexec_buffer() at
> kexec 'execute'.
> 
> Set the priority of register_reboot_notifier to INT_MIN to ensure that the
> IMA log copy operation will happen at the end of the operation chain, so
> that all the IMA measurement records extended into the TPM are copied
> 
> Co-developed-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Dave Young <dyoung@redhat.com>
> Signed-off-by: Steven Chen <chenste@linux.microsoft.com>
> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
> Acked-by: Baoquan He <bhe@redhat.com>

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>

> ---
>   include/linux/ima.h                |  3 ++
>   security/integrity/ima/ima_kexec.c | 47 ++++++++++++++++++++++++++++++
>   2 files changed, 50 insertions(+)
> 
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 0bae61a15b60..8e29cb4e6a01 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -32,6 +32,9 @@ static inline void ima_appraise_parse_cmdline(void) {}
>   
>   #ifdef CONFIG_IMA_KEXEC
>   extern void ima_add_kexec_buffer(struct kimage *image);
> +extern void ima_kexec_post_load(struct kimage *image);
> +#else
> +static inline void ima_kexec_post_load(struct kimage *image) {}
>   #endif
>   
>   #else
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index 7e0a19c3483f..e79f6caf895b 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -12,10 +12,14 @@
>   #include <linux/kexec.h>
>   #include <linux/of.h>
>   #include <linux/ima.h>
> +#include <linux/reboot.h>
> +#include <asm/page.h>
>   #include "ima.h"
>   
>   #ifdef CONFIG_IMA_KEXEC
> +static bool ima_kexec_update_registered;
>   static struct seq_file ima_kexec_file;
> +static void *ima_kexec_buffer;
>   
>   static void ima_free_kexec_file_buf(struct seq_file *sf)
>   {
> @@ -162,6 +166,49 @@ void ima_add_kexec_buffer(struct kimage *image)
>   	kexec_dprintk("kexec measurement buffer for the loaded kernel at 0x%lx.\n",
>   		      kbuf.mem);
>   }
> +
> +/*
> + * Called during kexec execute so that IMA can update the measurement list.
> + */
> +static int ima_update_kexec_buffer(struct notifier_block *self,
> +				   unsigned long action, void *data)
> +{
> +	return NOTIFY_OK;
> +}
> +
> +static struct notifier_block update_buffer_nb = {
> +	.notifier_call = ima_update_kexec_buffer,
> +	.priority = INT_MIN
> +};
> +
> +/*
> + * Create a mapping for the source pages that contain the IMA buffer
> + * so we can update it later.
> + */
> +void ima_kexec_post_load(struct kimage *image)
> +{
> +	if (ima_kexec_buffer) {
> +		kimage_unmap_segment(ima_kexec_buffer);
> +		ima_kexec_buffer = NULL;
> +	}
> +
> +	if (!image->ima_buffer_addr)
> +		return;
> +
> +	ima_kexec_buffer = kimage_map_segment(image,
> +					      image->ima_buffer_addr,
> +					      image->ima_buffer_size);
> +	if (!ima_kexec_buffer) {
> +		pr_err("Could not map measurements buffer.\n");
> +		return;
> +	}
> +
> +	if (!ima_kexec_update_registered) {
> +		register_reboot_notifier(&update_buffer_nb);
> +		ima_kexec_update_registered = true;
> +	}
> +}
> +
>   #endif /* IMA_KEXEC */
>   
>   /*