diff mbox series

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

Message ID 20231123073652.507034-2-bhe@redhat.com
State New
Headers
Series kernel/Kconfig.kexec: drop select of KEXEC for CRASH_DUMP |

Commit Message

Baoquan He Nov. 23, 2023, 7:36 a.m. UTC 
  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@redhat.com>
---
 arch/arm/include/asm/kexec.h | 4 ----
 kernel/Kconfig.kexec         | 1 -
 2 files changed, 5 deletions(-)

Comments

Ignat Korchagin Nov. 23, 2023, 8:23 a.m. UTC | #1 
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
>
Baoquan He Nov. 23, 2023, 11:07 a.m. UTC | #2 
On 11/23/23 at 08:23am, Ignat Korchagin wrote:
> 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

Oops, I forgot this part. This should fix the link error.

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 mbox series

Patch

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