Re: [PATCH v3 5/7] ima: suspend measurements during buffer copy at kexec execute

[Mimi Zohar <zohar@linux.ibm.com>]

On Fri, 2023-12-15 at 17:07 -0800, Tushar Sugandhi wrote:
> If the new measurements are added to the IMA log while it is being 
> being copied to the kexec buffer during kexec 'execute', it can miss
> copying those new measurements to the kexec buffer, and the buffer can go
> out of sync with TPM PCRs.  This could result in breaking the integrity
> of the measurements after the kexec soft reboot to the new Kernel.
> 
> Add a check in the ima_add_template_entry() function not to measure
> events and return from the function early when 'suspend_ima_measurements'
> flag is set.
> 
> This ensures the consistency of the IMA measurement list while copying 
> them to the kexec buffer.  When the 'suspend_ima_measurements' flag is
> set, any new measurements will be ignored until the flag is unset.  This
> allows the buffer to be safely copied without worrying about concurrent
> modifications to the measurement list.  This is crucial for maintaining
> the integrity of the measurements during a kexec soft reboot.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> ---
>  security/integrity/ima/ima_queue.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> index cb9abc02a304..5946a26a2849 100644
> --- a/security/integrity/ima/ima_queue.c
> +++ b/security/integrity/ima/ima_queue.c
> @@ -195,6 +195,19 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
>  		}
>  	}
>  
> +	/*
> +	 * suspend_ima_measurements will be set if the system is
> +	 * undergoing kexec soft boot to a new kernel.
> +	 * suspending measurements in this short window ensures the
> +	 * consistency of the IMA measurement list during copying
> +	 * of the kexec buffer.
> +	 */
> +	if (atomic_read(&suspend_ima_measurements)) {
> +		audit_cause = "measurements_suspended";
> +		audit_info = 0;
> +		goto out;
> +	}
> +
>  	result = ima_add_digest_entry(entry,
>  				      !IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE));
>  	if (result < 0) {

I assume you meant to include the suspend/resume code in "ima: kexec:
move ima log copy from kexec load to execute"  in this patch.

-- 
thanks,

Mimi