Re: [PATCH v2] kernel/Kconfig.kexec: drop select of KEXEC for CRASH_DUMP

From: Eric DeVolder <eric_devolder@yahoo.com>
To: Baoquan He <bhe@redhat.com>, linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org,
	akpm@linux-foundation.org, ignat@cloudflare.com,
	agordeev@linux.ibm.com
Subject: Re: [PATCH v2] kernel/Kconfig.kexec: drop select of KEXEC for CRASH_DUMP
Date: Tue, 28 Nov 2023 17:35:47 -0600	[thread overview]
Message-ID: <f876d8e6-cb93-4d22-9837-eae2764e7b07@yahoo.com> (raw)
In-Reply-To: <20231128054457.659452-1-bhe@redhat.com>

On 11/27/23 23:44, 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(-)
>
> diff --git a/arch/arm/include/asm/kexec.h b/arch/arm/include/asm/kexec.h
> index e62832dcba76..a8287e7ab9d4 100644
> --- a/arch/arm/include/asm/kexec.h
> +++ b/arch/arm/include/asm/kexec.h
> @@ -2,8 +2,6 @@
>   #ifndef _ARM_KEXEC_H
>   #define _ARM_KEXEC_H
>   
> -#ifdef CONFIG_KEXEC
> -
>   /* Maximum physical address we can use pages from */
>   #define KEXEC_SOURCE_MEMORY_LIMIT (-1UL)
>   /* Maximum address we can reach in physical address mode */
> @@ -82,6 +80,4 @@ static inline struct page *boot_pfn_to_page(unsigned long boot_pfn)
>   
>   #endif /* __ASSEMBLY__ */
>   
> -#endif /* CONFIG_KEXEC */
> -
>   #endif /* _ARM_KEXEC_H */
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index d53f56d6f840..771264d4726a 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -59,7 +59,7 @@ obj-$(CONFIG_FUNCTION_TRACER)	+= entry-ftrace.o
>   obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o insn.o patch.o
>   obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o insn.o patch.o
>   obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o insn.o patch.o
> -obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
> +obj-$(CONFIG_KEXEC_CORE)	+= machine_kexec.o relocate_kernel.o
>   # Main staffs in KPROBES are in arch/arm/probes/ .
>   obj-$(CONFIG_KPROBES)		+= patch.o insn.o
>   obj-$(CONFIG_OABI_COMPAT)	+= sys_oabi-compat.o
> diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec
> index 7aff28ded2f4..1cc3b1c595d7 100644
> --- a/kernel/Kconfig.kexec
> +++ b/kernel/Kconfig.kexec
> @@ -97,7 +97,6 @@ config CRASH_DUMP
>   	depends on ARCH_SUPPORTS_KEXEC
>   	select CRASH_CORE
>   	select KEXEC_CORE
> -	select KEXEC
>   	help
>   	  Generate crash dump after being started by kexec.
>   	  This should be normally only set in special crash dump kernels

I have run this change against the kconfig regression script, and it did 
not find any differences!

Reviewed-by: Eric DeVolder <eric_devolder@yahoo.com>

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec