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

Eric DeVolder
2023-07-07T12:17:07Z

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@oracle.com>
>> ---
>> 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)