Re: [PATCH v5 12/13] ima: Return error on deleting measurements already copied during kexec

On Fri, 2026-05-29 at 16:59 +0200, Roberto Sassu wrote:
> On Tue, 2026-05-26 at 10:02 -0400, Mimi Zohar wrote:
> > On Wed, 2026-04-29 at 18:03 +0200, Roberto Sassu wrote:
> > > From: Roberto Sassu <[email protected]>
> > > 
> > > Refuse to delete staged or active list measurements, if a kexec racing with
> > > the deletion already copied those measurements in the kexec buffer. In this
> > > way, user space becomes aware that those measurements are going to appear
> > > in the secondary kernel, and thus they don't have to be saved twice.
> > 
> > There are two reboot notifiers: one to prevent additional measurements extending
> > the TPM, while the other copies the measurements for kexec.  This patch prevents
> > deleting the staged measurements after the latter notifier.
> > 
> > Instead of introducing a specific method for detecting whether the measurement
> > list has been copied, rely on one of the two existing reboot notifiers. The
> > simplest method would test "ima_measurements_suspended", which would prevent
> > deleting the staged measurements a bit earlier.
> 
> Testing that the reboot notifier fired (with the
> ima_measurements_suspended variable) is not enough to know whether the
> measurements dump took place or not.
> 
> We need a flag (one is enough) protected by ima_extend_list_mutex, so
> that we know reliably which event occurred first, or the dump or the
> staging/delete (which are also protected by ima_extend_list_mutex).

I'm suggesting not allowing the staged measurements, if there are any, to be
deleted once the reboot notifier has started. They'll be copied at the late
reboot notifier.

Mimi