linux-kernel - [PATCH 1/3] kernel/Kconfig.kexec: drop select of KEXEC for CRASH

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Message-ID: <20231123073652.507034-2-bhe@redhat.com>
Date:   Thu, 23 Nov 2023 15:36:50 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-s390@...r.kernel.org, akpm@...ux-foundation.org,
        ignat@...udflare.com, eric_devolder@...oo.com,
        Baoquan He <bhe@...hat.com>
Subject: [PATCH 1/3] kernel/Kconfig.kexec: drop select of KEXEC for CRASH_DUMP

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.

Signed-off-by: Baoquan He <bhe@...hat.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