Re: [PATCH 1/3] kernel/Kconfig.kexec: drop select of KEXEC for CRASH_DUMP

Ignat Korchagin
2023-11-23T08:23:51Z

On Thu, Nov 23, 2023 at 7:37 AM Baoquan He <bhe@redhat.com> 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.

Hm... With the patch, when cross compiling for arm and
CONFIG_KEXEC_CORE=y
# CONFIG_KEXEC is not set
CONFIG_CRASH_DUMP=y

I get the following linker error at the end:

CALL scripts/checksyscalls.sh
UPD include/generated/utsversion.h
CC init/version-timestamp.o
LD .tmp_vmlinux.kallsyms1
arm-linux-gnueabi-ld: kernel/kexec_core.o: in function `kimage_free':
kexec_core.c:(.text+0xf5c): undefined reference to `machine_kexec_cleanup'
arm-linux-gnueabi-ld: kernel/kexec_core.o: in function `__crash_kexec':
kexec_core.c:(.text+0x15bc): undefined reference to `machine_crash_shutdown'
arm-linux-gnueabi-ld: kexec_core.c:(.text+0x15c4): undefined reference
to `machine_kexec'
arm-linux-gnueabi-ld: kernel/kexec_core.o: in function `kernel_kexec':
kexec_core.c:(.text+0x1a04): undefined reference to `machine_kexec'
make[2]: *** [scripts/Makefile.vmlinux:37: vmlinux] Error 1
make[1]: *** [/home/ignat/git/linux-upstream/Makefile:1154: vmlinux] Error 2
make: *** [Makefile:234: __sub-make] Error 2

> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
> arch/arm/include/asm/kexec.h | 4 ----
> kernel/Kconfig.kexec | 1 -
> 2 files changed, 5 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/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
> --
> 2.41.0
>