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

[Mimi Zohar]

On Fri, 2024-01-05 at 11:50 -0800, Tushar Sugandhi wrote:
> 
> On 12/20/23 12:44, Mimi Zohar wrote:
> > 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 at 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.
> > 
> 
> Sure, I can move the suspend/resume code from Patch 2/7 of this series
> to this patch (5/7).
> 
> Earlier I introduced the suspend/resume functionality in patch 2 because
> it was used in the functions in that patch.
> 
> But shifting it hear will make the patches cleaner.

Just a reminder this isn't the only issued mentioned in 2/7.  Please refer to it
for the other comments (e.g. make not including/verifying the IMA segment hash a
separate patch).

Before reposting, please remember to test after applying each patch in the patch
set to ensure that the measurement list is properly carried across kexec.
-- 
thanks,

Mimi