linux-kernel - Re: [PATCH v2 12/13] s390/kexec: refactor for kernel/Kconfig.kexec

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Date:   Thu, 22 Jun 2023 18:24:03 +0200
From:   Alexander Gordeev <agordeev@...ux.ibm.com>
To:     Eric DeVolder <eric.devolder@...cle.com>
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Subject: Re: [PATCH v2 12/13] s390/kexec: refactor for kernel/Kconfig.kexec

On Wed, Jun 21, 2023 at 12:10:49PM -0500, Eric DeVolder wrote:
Hi Eric,
...
> > > NOTE: The original Kconfig has a KEXEC_SIG which depends on
> > > MODULE_SIG_FORMAT. However, attempts to keep the MODULE_SIG_FORMAT
> > > dependency (using the strategy outlined in this series, and other
> > > techniques) results in 'error: recursive dependency detected'
> > > on CRYPTO. This occurs due to any path through KEXEC_SIG
> > > attempting to select CRYPTO is ultimately dependent upon CRYPTO:
> > > 
> > >   CRYPTO
> > >    <- ARCH_SUPPORTS_KEXEC_FILE
> > >       <- KEXEC_FILE
> > >          <- KEXEC_SIG
> > > 
> > > Therefore, the solution is to drop the MODULE_SIG_FORMAT dependency
> > > for KEXEC_SIG. In practice, however, MODULE_SIG_FORMAT is still
> > > configured-in as the use of KEXEC_SIG is in step with the use of
> > > SYSTEM_DATA_VERIFICATION, which does select MODULE_SIG_FORMAT.
> > 
> > No, it is actually the other way around.
> > Could you please provide the correct explanation?
> > 
> > AFAICT the MODULE_SIG_FORMAT dependency was introduced with commit
> > c8424e776b09 ("MODSIGN: Export module signature definitions") and
> > in fact was not necessary, since s390 did/does not use mod_check_sig()
> > anyway. So the SYSTEM_DATA_VERIFICATION could have left intact.
> 
> Thomas, would the correct explanation be simply indicating that
> MODULE_SIG_FORMAT isn't needed as it is not used by s390 (crediting your
> summary above)?

I guess, you asked me? Anyway, I will try to answer as if I were Thomas :)

MODULE_SIG_FORMAT is needed to select SYSTEM_DATA_VERIFICATION.
But SYSTEM_DATA_VERIFICATION is also selected by FS_VERITY*, so
dropping MODULE_SIG_FORMAT does not hurt.

Thanks!