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

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 <[email protected]>
>> ---
>>    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)