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

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Date:   Thu, 22 Jun 2023 12:51:41 -0500
From:   Eric DeVolder <eric.devolder@...cle.com>
To:     Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>, linux@...linux.org.uk,
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Subject: Re: [PATCH v2 12/13] s390/kexec: refactor for kernel/Kconfig.kexec



On 6/22/23 11:24, Alexander Gordeev wrote:
> 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!

For the commit message for this s390/Kconfig change, are you ok
with the following?
eric

=====
The kexec and crash kernel options are provided in the common
kernel/Kconfig.kexec. Utilize the common options and provide
the ARCH_SUPPORTS_ and ARCH_SELECTS_ entries to recreate the
equivalent set of KEXEC and CRASH options.

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.

Per Alexander Gordeev <agordeev@...ux.ibm.com>: "the MODULE_SIG_FORMAT
dependency was introduced with c8424e776b09 ("MODSIGN: Export module
signature definitions") and in fact was not necessary, since s390
did/does not use mod_check_sig() anyway. 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."

Therefore, the solution is to drop the MODULE_SIG_FORMAT dependency
from KEXEC_SIG.