Re: [PATCH] x86/kexec: Add a sanity check on previous kernel's ima kexec buffer

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

[Cc: Roberto Sassu, linux-integrity]

On Tue, 2025-12-02 at 08:16 +0100, Ard Biesheuvel wrote:
> On Mon, 1 Dec 2025 at 22:43, Mimi Zohar <zohar@linux.ibm.com> wrote:
> > 
> > On Mon, 2025-12-01 at 15:03 +0530, Harshit Mogalapalli wrote:
> > > Hi all,
> > > 
> > > On 13/11/25 01:00, Harshit Mogalapalli wrote:
> > > > When the second-stage kernel is booted via kexec with a limiting command
> > > > line such as "mem=<size>", the physical range that contains the carried
> > > > over IMA measurement list may fall outside the truncated RAM leading to
> > > > a kernel panic.
> > > > 
> > > >      BUG: unable to handle page fault for address: ffff97793ff47000
> > > >      RIP: ima_restore_measurement_list+0xdc/0x45a
> > > >      #PF: error_code(0x0000) – not-present page
> > > > 
> > > > Other architectures already validate the range with page_is_ram(), as
> > > > done in commit: cbf9c4b9617b ("of: check previous kernel's
> > > > ima-kexec-buffer against memory bounds") do a similar check on x86.
> > 
> > It should be obvious that without carrying the measurement list across kexec,
> > that attestation will fail.  Please mention it here in the patch description.
> > 
> 
> Couldn't we just use memremap() and be done with it? That will use the
> direct map if the memory is mapped, or vmap() it otherwise.

No, the IMA measurement list is not a continuous buffer, but a linked list of
records with varying types of fields and field sizes.  The call to
ima_dump_measurement_list() marshals the measurement list into a buffer, while
ima_restore_measurement_list() unmarshals it.

-- 
thanks,

Mimi