Re: [PATCH] ima: require signed IMA policy when UEFI secure boot is enabled

[Coiby Xu]

On Tue, Jul 04, 2023 at 08:57:10AM -0400, Mimi Zohar wrote:
> On Mon, 2023-07-03 at 19:54 +0800, Coiby Xu wrote:
> > With the introduction of the .machine keyring for UEFI-based systems,
> > users are able to add custom CAs keys via MOK. This allow users to sign
> > their own IMA polices. For the sake of security, mandate signed IMA
> > policy when UEFI secure boot is enabled.
> >
> > Suggested-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> > Signed-off-by: Coiby Xu <coxu@xxxxxxxxxx>
> > ---
> >  security/integrity/ima/ima_efi.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/security/integrity/ima/ima_efi.c b/security/integrity/ima/ima_efi.c
> > index 9db66fe310d4..bb2881759505 100644
> > --- a/security/integrity/ima/ima_efi.c
> > +++ b/security/integrity/ima/ima_efi.c
> > @@ -58,6 +58,9 @@ static const char * const sb_arch_rules[] = {
> >  #if !IS_ENABLED(CONFIG_MODULE_SIG)
> >  	"appraise func=MODULE_CHECK appraise_type=imasig",
> >  #endif
> > +#if IS_ENABLED(CONFIG_INTEGRITY_MACHINE_KEYRING) && IS_ENABLED(CONFIG_IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY)
> > +	"appraise func=POLICY_CHECK appraise_type=imasig",
> > +#endif /* CONFIG_INTEGRITY_MACHINE_KEYRING && IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY */
> >  	"measure func=MODULE_CHECK",
> >  	NULL
> >  };
>
> Thanks, Coiby.

You are welcome!

> Using IS_ENABLED() is not wrong, but unnecessary.  IS_BUILTIN()
> suffices.

Thanks for the reminding! When I was going to apply this suggestion, I
noticed ima_efi.c uses IS_ENABLED for all configuration items i.e.
CONFIG_MODULE_SIG and CONFIG_KEXEC_SIG which are all of bool type. Would
you like me to switch all IS_ENABLEs to IS_BUILTIN or still use
IS_ENABLED? While IS_BUILTIN is exclusively for bool type, it's not as
intuitive as IS_ENABLED. So it's not easy for me to make a choice.

> --
> thanks,
>
> Mimi

--
Best regards,
Coiby