Re: [PATCH v2 12/13] s390/kexec: refactor for kernel/Kconfig.kexec

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On 6/21/23 00:00, Alexander Gordeev wrote:
On Mon, Jun 19, 2023 at 10:58:00AM -0400, Eric DeVolder wrote:

Hi Eric,

The kexec and crash kernel options are provided in the common
kernel/Kconfig.kexec. Utilize the common options and provide
the ARCH_SUPPORTS_ and ARCH_SELECTS_ entries to recreate the
equivalent set of KEXEC and CRASH options.

NOTE: The original Kconfig has a KEXEC_SIG which depends on
MODULE_SIG_FORMAT. However, attempts to keep the MODULE_SIG_FORMAT
dependency (using the strategy outlined in this series, and other
techniques) results in 'error: recursive dependency detected'
on CRYPTO. This occurs due to any path through KEXEC_SIG
attempting to select CRYPTO is ultimately dependent upon CRYPTO:

      <- KEXEC_FILE
         <- KEXEC_SIG

Therefore, the solution is to drop the MODULE_SIG_FORMAT dependency
for KEXEC_SIG. In practice, however, MODULE_SIG_FORMAT is still
configured-in as the use of KEXEC_SIG is in step with the use of

No, it is actually the other way around.
Could you please provide the correct explanation?

AFAICT the MODULE_SIG_FORMAT dependency was introduced with commit
c8424e776b09 ("MODSIGN: Export module signature definitions") and
in fact was not necessary, since s390 did/does not use mod_check_sig()
anyway. So the SYSTEM_DATA_VERIFICATION could have left intact.

Thomas, would the correct explanation be simply indicating that MODULE_SIG_FORMAT isn't needed as it is not used by s390 (crediting your summary above)?

However, the original SYSTEM_DATA_VERIFICATION seems sane and I do
not understand why other architectures do not have it also? May be
Mimi Zohar (putting on CC) could explain that?

It looks like such dependency actually exists in implicit form
(which you picked from x86):

	In addition to this option, you need to enable signature
	verification for the corresponding kernel image type being
	loaded in order for this to work.

Does it mean that if an architecture did not enable the signature
verification type explicitly the linker could fail - both before
and after you series?

As a quick test I checked x86 and it compiles/links ok if KEXEC_SIG and KEXEC_SIG_FORCE are configured-in, but KEXEC_BZIMAGE_VERIFY_SIG (used for x86 sig verify) is not. The reason being that the kexec_image_verify_sig() function checks if the fops.verify_sig is non-NULL before invoking the verification. If it is NULL, the sig check fails. This would appear to be valid outcome for other archs as well.

At any rate, I think attempting to determine if other archs need SYSTEM_DATA_VERIFICATION is out of the scope of this series; I'm targeting just the refactor to be equivalent to what is what prior.

Thanks for looking at this!


Not ideal, but results in equivalent .config files for s390.

Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
  arch/s390/Kconfig | 65 ++++++++++++++---------------------------------
  1 file changed, 19 insertions(+), 46 deletions(-)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 6dab9c1be508..58dc124433ca 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -243,6 +243,25 @@ config PGTABLE_LEVELS
source "kernel/livepatch/Kconfig" +config ARCH_DEFAULT_KEXEC
+	def_bool y
+	def_bool y
+	def_bool CRYPTO && CRYPTO_SHA256 && CRYPTO_SHA256_S390
+	def_bool KEXEC_FILE
+	def_bool y
+	help
+	  Refer to <file:Documentation/s390/zfcpdump.rst> for more details on this.
+	  This option also enables s390 zfcpdump.
+	  See also <file:Documentation/s390/zfcpdump.rst>
  menu "Processor type and features"
@@ -481,36 +500,6 @@ config SCHED_TOPOLOGY
source "kernel/Kconfig.hz" -config KEXEC
-	def_bool y
-	select KEXEC_CORE
-config KEXEC_FILE
-	bool "kexec file based system call"
-	select KEXEC_CORE
-	depends on CRYPTO
-	depends on CRYPTO_SHA256
-	depends on CRYPTO_SHA256_S390
-	help
-	  Enable the kexec file based system call. In contrast to the normal
-	  kexec system call this system call takes file descriptors for the
-	  kernel and initramfs as arguments.
-	def_bool y
-	depends on KEXEC_FILE
-config KEXEC_SIG
-	bool "Verify kernel signature during kexec_file_load() syscall"
-	help
-	  This option makes kernel signature verification mandatory for
-	  the kexec_file_load() syscall.
-	  In addition to that option, you need to enable signature
-	  verification for the corresponding kernel image type being
-	  loaded in order for this to work.
  config KERNEL_NOBP
  	def_bool n
  	prompt "Enable modified branch prediction for the kernel by default"
@@ -732,22 +721,6 @@ config VFIO_AP
endmenu -menu "Dump support"
-config CRASH_DUMP
-	bool "kernel crash dumps"
-	select KEXEC
-	help
-	  Generate crash dump after being started by kexec.
-	  Crash dump kernels are loaded in the main kernel with kexec-tools
-	  into a specially reserved region and then later executed after
-	  a crash by kdump/kexec.
-	  Refer to <file:Documentation/s390/zfcpdump.rst> for more details on this.
-	  This option also enables s390 zfcpdump.
-	  See also <file:Documentation/s390/zfcpdump.rst>
  config CCW
  	def_bool y

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