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Date:   Tue, 21 Nov 2023 09:50:05 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Ignat Korchagin <ignat@cloudflare.com>, eric_devolder@yahoo.com
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Subject: Re: Potential config regression after 89cde455 ("kexec: consolidate
 kexec and crash options into kernel/Kconfig.kexec")
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References: <CALrw=nHpRQQaQTP_jZfREgrQEMpS8jBF8JQCv4ygqXycE-StaA@mail.gmail.com>
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Eric DeVolder's Oracle mail address is not available anymore, add his
current mail address he told me. 

On 11/20/23 at 10:52pm, Ignat Korchagin wrote:
> Good day!
> 
> We have recently started to evaluate Linux 6.6 and noticed that we
> cannot disable CONFIG_KEXEC anymore, but keep CONFIG_CRASH_DUMP
> enabled. It seems to be related to commit 89cde455 ("kexec:
> consolidate kexec and crash options into kernel/Kconfig.kexec"), where
> a CONFIG_KEXEC dependency was added to CONFIG_CRASH_DUMP.
> 
> In our current kernel (Linux 6.1) we only enable CONFIG_KEXEC_FILE
> with enforced signature check to support the kernel crash dumping
> functionality and would like to keep CONFIG_KEXEC disabled for
> security reasons [1].
> 
> I was reading the long commit message, but the reason for adding
> CONFIG_KEXEC as a dependency for CONFIG_CRASH_DUMP evaded me. And I
> believe from the implementation perspective CONFIG_KEXEC_FILE should
> suffice here (as we successfully used it for crashdumps on Linux 6.1).
> 
> Is there a reason for adding this dependency or is it just an
> oversight? Would some solution of requiring either CONFIG_KEXEC or
> CONFIG_KEXEC_FILE work here?

I searched the patch history, found Eric didn't add the dependency on
CONFIG_KEXEC at the beginning. Later a linux-next building failure with
randconfig was reported, in there CONFIG_CRASH_DUMP enabled, while
CONFIG_KEXEC is disabled. Finally Eric added the KEXEC dependency for
CRASH_DUMP. Please see below link for more details:

https://lore.kernel.org/all/3e8eecd1-a277-2cfb-690e-5de2eb7b988e@oracle.com/T/#u

And besides, the newly added CONFIG_CRASH_HOTPLUG also needs
CONFIG_KEXEC if the elfcorehdr is allowed to be manipulated when
cpu/memory hotplug hapened.

Thanks
Baoquan