Re: [PATCH v5 02/13] x86/kexec: refactor for kernel/Kconfig.kexec

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On 7/7/23 00:58, Christophe Leroy wrote:


Le 07/07/2023 à 00:20, Eric DeVolder a écrit :
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.


Why do you need to duplicate the ARCH_SELECTS_ entries in each
architecture ?

Why not define them in arch/Kconfig then select if from each architecture ?

For instance here for x86 for ARCH_SELECTS_KEXEC_FILE all you'll have to
do is:
	select ARCH_SELECTS_KEXEC_FILE if KEXEC_FILE
	select HAVE_IMA_KEXEC if IMA && KEXEC_FILE


Christophe

Hi Christophe, thanks for looking at this!
The ARCH_SELECTS_ is where the "customization" is performed for that option. The customization is putting in place the differences that the arch had from the common option.

For example, with ARCH_SELECTS_KEXEC_FILE, here are all the uses:

x86:
    select HAVE_IMA_KEXEC if IMA

arm64:
    select HAVE_IMA_KEXEC if IMA

powerpc:
    select KEXEC_ELF
    select HAVE_IMA_KEXEC if IMA

riscv:
    select HAVE_IMA_KEXEC if IMA
    select KEXEC_ELF

And there are archs (parisc, riscv, s390) that support KEXEC_FILE that do not need ARCH_SELECTS_KEXEC_FILE.

So there isn't a clear path for optimizing the IMA statement, in this example, that I'm aware of.

But perhaps I don't quite understand the technique you are suggesting, either...

eric





Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
---
   arch/x86/Kconfig | 92 ++++++++++--------------------------------------
   1 file changed, 19 insertions(+), 73 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7422db409770..9767a343f7c2 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2040,88 +2040,34 @@ config EFI_RUNTIME_MAP
source "kernel/Kconfig.hz" -config KEXEC
-	bool "kexec system call"
-	select KEXEC_CORE
-	help
-	  kexec is a system call that implements the ability to shutdown your
-	  current kernel, and to start another kernel.  It is like a reboot
-	  but it is independent of the system firmware.   And like a reboot
-	  you can start any kernel with it, not just Linux.
-
-	  The name comes from the similarity to the exec system call.
-
-	  It is an ongoing process to be certain the hardware in a machine
-	  is properly shutdown, so do not be surprised if this code does not
-	  initially work for you.  As of this writing the exact hardware
-	  interface is strongly in flux, so no good recommendation can be
-	  made.
-
-config KEXEC_FILE
-	bool "kexec file based system call"
-	select KEXEC_CORE
-	select HAVE_IMA_KEXEC if IMA
-	depends on X86_64
-	depends on CRYPTO=y
-	depends on CRYPTO_SHA256=y
-	help
-	  This is new version of kexec system call. This system call is
-	  file based and takes file descriptors as system call argument
-	  for kernel and initramfs as opposed to list of segments as
-	  accepted by previous system call.
+config ARCH_SUPPORTS_KEXEC
+	def_bool y
-config ARCH_HAS_KEXEC_PURGATORY
-	def_bool KEXEC_FILE
+config ARCH_SUPPORTS_KEXEC_FILE
+	def_bool X86_64 && CRYPTO && CRYPTO_SHA256
-config KEXEC_SIG
-	bool "Verify kernel signature during kexec_file_load() syscall"
+config ARCH_SELECTS_KEXEC_FILE
+	def_bool y
   	depends on KEXEC_FILE
-	help
+	select HAVE_IMA_KEXEC if IMA
- This option makes the kexec_file_load() syscall check for a valid
-	  signature of the kernel image.  The image can still be loaded without
-	  a valid signature unless you also enable KEXEC_SIG_FORCE, though if
-	  there's a signature that we can check, then it must be valid.
+config ARCH_HAS_KEXEC_PURGATORY
+	def_bool KEXEC_FILE
- 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.
+config ARCH_SUPPORTS_KEXEC_SIG
+	def_bool y
-config KEXEC_SIG_FORCE
-	bool "Require a valid signature in kexec_file_load() syscall"
-	depends on KEXEC_SIG
-	help
-	  This option makes kernel signature verification mandatory for
-	  the kexec_file_load() syscall.
+config ARCH_SUPPORTS_KEXEC_SIG_FORCE
+	def_bool y
-config KEXEC_BZIMAGE_VERIFY_SIG
-	bool "Enable bzImage signature verification support"
-	depends on KEXEC_SIG
-	depends on SIGNED_PE_FILE_VERIFICATION
-	select SYSTEM_TRUSTED_KEYRING
-	help
-	  Enable bzImage signature verification support.
+config ARCH_SUPPORTS_KEXEC_BZIMAGE_VERIFY_SIG
+	def_bool y
-config CRASH_DUMP
-	bool "kernel crash dumps"
-	depends on X86_64 || (X86_32 && HIGHMEM)
-	help
-	  Generate crash dump after being started by kexec.
-	  This should be normally only set in special crash dump kernels
-	  which are loaded in the main kernel with kexec-tools into
-	  a specially reserved region and then later executed after
-	  a crash by kdump/kexec. The crash dump kernel must be compiled
-	  to a memory address not used by the main kernel or BIOS using
-	  PHYSICAL_START, or it must be built as a relocatable image
-	  (CONFIG_RELOCATABLE=y).
-	  For more details see Documentation/admin-guide/kdump/kdump.rst
+config ARCH_SUPPORTS_KEXEC_JUMP
+	def_bool y
-config KEXEC_JUMP
-	bool "kexec jump"
-	depends on KEXEC && HIBERNATION
-	help
-	  Jump between original kernel and kexeced kernel and invoke
-	  code in physical address mode via KEXEC
+config ARCH_SUPPORTS_CRASH_DUMP
+	def_bool X86_64 || (X86_32 && HIGHMEM)
config PHYSICAL_START
   	hex "Physical address where the kernel is loaded" if (EXPERT || CRASH_DUMP)



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