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Date:   Thu, 22 Jun 2023 12:51:41 -0500
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Subject: Re: [PATCH v2 12/13] s390/kexec: refactor for kernel/Kconfig.kexec
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To:     Alexander Gordeev <agordeev@linux.ibm.com>
Cc:     Mimi Zohar <zohar@linux.ibm.com>, linux@armlinux.org.uk,
        catalin.marinas@arm.com, will@kernel.org, chenhuacai@kernel.org,
        geert@linux-m68k.org, tsbogend@alpha.franken.de,
        James.Bottomley@hansenpartnership.com, deller@gmx.de,
        ysato@users.sourceforge.jp, dalias@libc.org,
        glaubitz@physik.fu-berlin.de, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-ia64@vger.kernel.org, loongarch@lists.linux.dev,
        linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
        linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-sh@vger.kernel.org, kernel@xen0n.name, mpe@ellerman.id.au,
        npiggin@gmail.com, christophe.leroy@csgroup.eu,
        paul.walmsley@sifive.com, palmer@dabbelt.com,
        aou@eecs.berkeley.edu, hca@linux.ibm.com, gor@linux.ibm.com,
        borntraeger@linux.ibm.com, svens@linux.ibm.com, hpa@zytor.com,
        keescook@chromium.org, paulmck@kernel.org, peterz@infradead.org,
        frederic@kernel.org, akpm@linux-foundation.org, ardb@kernel.org,
        samitolvanen@google.com, juerg.haefliger@canonical.com,
        arnd@arndb.de, rmk+kernel@armlinux.org.uk,
        linus.walleij@linaro.org, sebastian.reichel@collabora.com,
        rppt@kernel.org, kirill.shutemov@linux.intel.com,
        anshuman.khandual@arm.com, ziy@nvidia.com, masahiroy@kernel.org,
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        gregkh@linuxfoundation.org, tsi@tuyoix.net, bhe@redhat.com,
        hbathini@linux.ibm.com, sourabhjain@linux.ibm.com,
        boris.ostrovsky@oracle.com, konrad.wilk@oracle.com
References: <20230619145801.1064716-1-eric.devolder@oracle.com>
 <20230619145801.1064716-13-eric.devolder@oracle.com>
 <ZJKD690QaX1IgiAz@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
 <b89bb8d6-77db-76fe-e360-f6c439b80e73@oracle.com>
 <ZJR1o0lzhIUdpTb+@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <ZJR1o0lzhIUdpTb+@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
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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@linux.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.