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Date:   Tue, 28 Nov 2023 14:33:38 +0100
From:   Alexander Gordeev <agordeev@linux.ibm.com>
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org,
        ignat@cloudflare.com, eric_devolder@yahoo.com
Subject: Re: [PATCH v2] kernel/Kconfig.kexec: drop select of KEXEC for
 CRASH_DUMP
Message-ID: <ZWXsMvkf8vvRUpYR@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
References: <20231128054457.659452-1-bhe@redhat.com>
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On Tue, Nov 28, 2023 at 01:44:57PM +0800, Baoquan He wrote:
> Ignat Korchagin complained that a potential config regression was
> introduced by commit 89cde455915f ("kexec: consolidate kexec and
> crash options into kernel/Kconfig.kexec"). Before the commit,
> CONFIG_CRASH_DUMP has no dependency on CONFIG_KEXEC. After the commit,
> CRASH_DUMP selects KEXEC. That enforces system to have CONFIG_KEXEC=y
> as long as CONFIG_CRASH_DUMP=Y which people may not want.
> 
> In Ignat's case, he sets CONFIG_CRASH_DUMP=y, CONFIG_KEXEC_FILE=y and
> CONFIG_KEXEC=n because kexec_load interface could have security issue if
> kernel/initrd has no chance to be signed and verified.
> 
> CRASH_DUMP has select of KEXEC because Eric, author of above commit,
> met a LKP report of build failure when posting patch of earlier version.
> Please see below link to get detail of the LKP report:
> 
>     https://lore.kernel.org/all/3e8eecd1-a277-2cfb-690e-5de2eb7b988e@oracle.com/T/#u
> 
> In fact, that LKP report is triggered because arm's <asm/kexec.h> is
> wrapped in CONFIG_KEXEC ifdeffery scope. That is wrong. CONFIG_KEXEC
> controls the enabling/disabling of kexec_load interface, but not kexec
> feature. Removing the wrongly added CONFIG_KEXEC ifdeffery scope in
> <asm/kexec.h> of arm allows us to drop the select KEXEC for CRASH_DUMP.
> Meanwhile, change arch/arm/kernel/Makefile to let machine_kexec.o
> relocate_kernel.o depend on KEXEC_CORE.
> 
> Fixes: commit 89cde455915f ("kexec: consolidate kexec and crash options into kernel/Kconfig.kexec")
> Reported-by: Ignat Korchagin <ignat@cloudflare.com>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  arch/arm/include/asm/kexec.h | 4 ----
>  arch/arm/kernel/Makefile     | 2 +-
>  kernel/Kconfig.kexec         | 1 -
>  3 files changed, 1 insertion(+), 6 deletions(-)

On s390:
Tested-by: Alexander Gordeev <agordeev@linux.ibm.com>

Thanks!