Re: [PATCH] lockdown: kexec_file: prevent unsigned kernel image when KEXEC_SIG not enabled

[Coiby Xu]

On Mon, Nov 28, 2022 at 12:16:08PM -0500, Mimi Zohar wrote:
> On Tue, 2022-11-22 at 10:36 +0800, Coiby Xu wrote:
> > Hi Mimi,
> >
> > On Mon, Nov 21, 2022 at 01:23:57PM -0500, Mimi Zohar wrote:
> > >Hi Coiby,
> > >
> > >On Mon, 2022-11-21 at 15:29 +0800, Coiby Xu wrote:
> > >> A kernel builder may not enable KEXEC_SIG and some architectures like
> > >> ppc64 simply don't have KEXEC_SIG. In these cases, unless both
> > >> IMA_ARCH_POLICY and secure boot also enabled, lockdown doesn't prevent
> > >> unsigned kernel image from being kexec'ed via the kexec_file_load
> > >> syscall whereas it could prevent one via the kexec_load syscall. Mandate
> > >> signature verification for those cases.
> > >>
> > >> Fixes: 155bdd30af17 ("kexec_file: Restrict at runtime if the kernel is locked down")
> > >> Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
> > >> Cc: Jiri Bohac <jbohac@xxxxxxx>
> > >> Cc: David Howells <dhowells@xxxxxxxxxx>
> > >> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> > >> Cc: linux-integrity@xxxxxxxxxxxxxxx
> > >> Signed-off-by: Coiby Xu <coxu@xxxxxxxxxx>
> > >
> > >Other than correcting the function name to mandate_signature_verificati
> > >on(),
> >
> > Applied to v2, thanks for correcting me! Btw, I realize I overwrote the
> > return code of kexec_image_verify_sig with
> > mandate_signature_verification's. v2 has fixed this issue as well.
> >
> > >
> > >Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> >
> > And thanks for the review!
>
> You're welcome.
>
> Without either IMA_ARCH or KEXEC_SIG enabled, the kexec selftest
> test_kexec_file_load.sh properly failed with "kexec_file_load failed
> [PASS]", but from the informational messages output, it isn't clear why
> it failed.  This should be corrected.

Thanks for the suggestion! I've added some tests in v3 and now the
message is "# kexec_file_load failed (missing IMA sig) [PASS]".

> --
> thanks,
>
> Mimi

--
Best regards,
Coiby