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From:   Ignat Korchagin <ignat@cloudflare.com>
Date:   Tue, 28 Nov 2023 11:50:38 +0000
Message-ID: <CALrw=nEe195PSJywrkr5sPh_PnrLXG+ytvryG8CB-LHvmXpJkg@mail.gmail.com>
Subject: Re: [PATCH v2] kernel/Kconfig.kexec: drop select of KEXEC for CRASH_DUMP
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,
        eric_devolder@yahoo.com, agordeev@linux.ibm.com,
        kernel-team <kernel-team@cloudflare.com>
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On Tue, Nov 28, 2023 at 5:45=E2=80=AFAM 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=3Dy
> as long as CONFIG_CRASH_DUMP=3DY which people may not want.
>
> In Ignat's case, he sets CONFIG_CRASH_DUMP=3Dy, CONFIG_KEXEC_FILE=3Dy and
> CONFIG_KEXEC=3Dn because kexec_load interface could have security issue i=
f
> 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@orac=
le.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 i=
nto kernel/Kconfig.kexec")
> Reported-by: Ignat Korchagin <ignat@cloudflare.com>
> Signed-off-by: Baoquan He <bhe@redhat.com>

Tested-by: Ignat Korchagin <ignat@cloudflare.com> # compile-time only
for x86 and arm

> ---
>  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 lo=
ng 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-$(CONFIG_FUNCTION_TRACER) +=3D entry-ftrace.o
>  obj-$(CONFIG_DYNAMIC_FTRACE)   +=3D ftrace.o insn.o patch.o
>  obj-$(CONFIG_FUNCTION_GRAPH_TRACER)    +=3D ftrace.o insn.o patch.o
>  obj-$(CONFIG_JUMP_LABEL)       +=3D jump_label.o insn.o patch.o
> -obj-$(CONFIG_KEXEC)            +=3D machine_kexec.o relocate_kernel.o
> +obj-$(CONFIG_KEXEC_CORE)       +=3D machine_kexec.o relocate_kernel.o
>  # Main staffs in KPROBES are in arch/arm/probes/ .
>  obj-$(CONFIG_KPROBES)          +=3D patch.o insn.o
>  obj-$(CONFIG_OABI_COMPAT)      +=3D 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
> --
> 2.41.0
>