[PATCH v2 00/13] refactor Kconfig to consolidate KEXEC and CRASH options

Eric DeVolder
2023-06-19T14:59:28Z

The Kconfig is refactored to consolidate KEXEC and CRASH options from
various arch/<arch>/Kconfig files into new file kernel/Kconfig.kexec.

The Kconfig.kexec is now a submenu titled "Kexec and crash features"
located under "General Setup".

The following options are impacted:

- KEXEC
- KEXEC_FILE
- KEXEC_SIG
- KEXEC_SIG_FORCE
- KEXEC_BZIMAGE_VERIFY_SIG
- KEXEC_JUMP
- CRASH_DUMP

Over time, these options have been copied between Kconfig files and
are very similar to one another, but with slight differences.

The following architectures are impacted by the refactor (because of
use of one or more KEXEC/CRASH options):

- arm
- arm64
- ia64
- loongarch
- m68k
- mips
- parisc
- powerpc
- riscv
- s390
- sh
- x86

More information:

In the patch series "crash: Kernel handling of CPU and memory hot
un/plug"

https://lore.kernel.org/lkml/20230503224145.7405-1-eric.devolder@oracle.com/

the new kernel feature introduces the config option CRASH_HOTPLUG.

In reviewing, Thomas Gleixner requested that the new config option
not be placed in x86 Kconfig. Rather the option needs a generic/common
home. To Thomas' point, the KEXEC and CRASH options have largely been
duplicated in the various arch/<arch>/Kconfig files, with minor
differences. This kind of proliferation is to be avoid/stopped.

https://lore.kernel.org/lkml/875y91yv63.ffs@tglx/

To that end, I have refactored the arch Kconfigs so as to consolidate
the various KEXEC and CRASH options. Generally speaking, this work has
the following themes:

- KEXEC and CRASH options are moved into new file kernel/Kconfig.kexec
- These items from arch/Kconfig:
CRASH_CORE KEXEC_CORE KEXEC_ELF HAVE_IMA_KEXEC
- These items from arch/x86/Kconfig form the common options:
KEXEC KEXEC_FILE KEXEC_SIG KEXEC_SIG_FORCE
KEXEC_BZIMAGE_VERIFY_SIG KEXEC_JUMP CRASH_DUMP
- The crash hotplug series appends CRASH_HOTPLUG to Kconfig.kexec
NOTE: PHYSICAL_START could be argued to be included in this series.
- The Kconfig.kexec is now a submenu titled "Kexec and crash features"
- The Kconfig.kexec is now listed in "General Setup" submenu from
init/Kconfig
- To control the main common options, new options ARCH_SUPPORTS_KEXEC,
ARCH_SUPPORTS_KEXEC_FILE and ARCH_SUPPORTS_CRASH_DUMP are introduced.
NOTE: The existing ARCH_HAS_KEXEC_PURGATORY remains unchanged.
- To account for the slight differences, new options ARCH_SELECTS_KEXEC,
ARCH_SELECTS_KEXEC_FILE and ARCH_SELECTS_CRASH_DUMP are used to
elicit the same side effects as the original arch/<arch>/Kconfig
files for KEXEC and CRASH options.

An example, 'make menuconfig' illustrating the submenu:

> General setup > Kexec and crash features
[*] Enable kexec system call
[*] Enable kexec file based system call
[*] Verify kernel signature during kexec_file_load() syscall
[ ] Require a valid signature in kexec_file_load() syscall
[ ] Enable bzImage signature verification support
[*] kexec jump
[*] kernel crash dumps
[*] Update the crash elfcorehdr on system configuration changes

The three main options are KEXEC, KEXEC_FILE and CRASH_DUMP. In the
process of consolidating these options, I encountered slight differences
in the coding of these options in several of the architectures. As a
result, I settled on the following solution:

- Each of three main options has a 'depends on ARCH_SUPPORTS_ '
statement: ARCH_SUPPORTS_KEXEC, ARCH_SUPPORTS_KEXEC_FILE,
ARCH_SUPPORTS_CRASH_DUMP.

For example, the KEXEC_FILE option has a 'depends on
ARCH_SUPPORTS_KEXEC_FILE' statement.

- The boolean ARCH_SUPPORTS_ in effect allows the arch to
determine when the feature is allowed. Archs which don't have the
feature simply do not provide the corresponding ARCH_SUPPORTS_ .
For each arch, where there previously were KEXEC and/or CRASH
options, these have been replaced with the corresponding boolean
ARCH_SUPPORTS_ , and an appropriate def_bool statement.

For example, if the arch supports KEXEC_FILE, then the
ARCH_SUPPORTS_KEXEC_FILE simply has a 'def_bool y'. This permits the
KEXEC_FILE option to be available.

If the arch has a 'depends on' statement in its original coding
of the option, then that expression becomes part of the def_bool
expression. For example, arm64 had:

config KEXEC
depends on PM_SLEEP_SMP

and in this solution, this converts to:

config ARCH_SUPPORTS_KEXEC
def_bool PM_SLEEP_SMP

- In order to account for the differences in the config coding for
the three common options, the ARCH_SELECTS_ is used.
This options has a 'depends on ' statement to couple it
to the main option, and from there can insert the differences
from the common option and the arch original coding of that option.

For example, a few archs enable CRYPTO and CRYTPO_SHA256 for
KEXEC_FILE. These require a ARCH_SELECTS_KEXEC_FILE and
'select CRYPTO' and 'select CRYPTO_SHA256' statements.

Illustrating the option relationships:

For KEXEC:
ARCH_SUPPORTS_KEXEC <- KEXEC <- ARCH_SELECTS_KEXEC

KEXEC # in Kconfig.kexec
ARCH_SUPPORTS_KEXEC # in arch/<arch>/Kconfig, as needed
ARCH_SELECTS_KEXEC # in arch/<arch>/Kconfig, as needed

For KEXEC_FILE:
ARCH_SUPPORTS_KEXEC_FILE <- KEXEC_FILE <- ARCH_SELECTS_KEXEC_FILE

KEXEC_FILE # in Kconfig.kexec
ARCH_SUPPORTS_KEXEC_FILE # in arch/<arch>/Kconfig, as needed
ARCH_SELECTS_KEXEC_FILE # in arch/<arch>/Kconfig, as needed

For CRASH:
ARCH_SUPPORTS_CRASH_DUMP <- CRASH_DUMP <- ARCH_SELECTS_CRASH_DUMP

CRASH_DUMP # in Kconfig.kexec
ARCH_SUPPORTS_CRASH_DUMP # in arch/<arch>/Kconfig, as needed
ARCH_SELECTS_CRASH_DUMP # in arch/<arch>/Kconfig, as needed

To summarize, the ARCH_SUPPORTS_ permits the to be
enabled, and the ARCH_SELECTS_ handles side effects (ie.
select statements).

Examples:
A few examples to show the new strategy in action:

===== x86 (minus the help section) =====
Original:
config KEXEC
bool "kexec system call"
select KEXEC_CORE

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

config ARCH_HAS_KEXEC_PURGATORY
def_bool KEXEC_FILE

config KEXEC_SIG
bool "Verify kernel signature during kexec_file_load() syscall"
depends on KEXEC_FILE

config KEXEC_SIG_FORCE
bool "Require a valid signature in kexec_file_load() syscall"
depends on KEXEC_SIG

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

config CRASH_DUMP
bool "kernel crash dumps"
depends on X86_64 || (X86_32 && HIGHMEM)

config KEXEC_JUMP
bool "kexec jump"
depends on KEXEC && HIBERNATION
help

becomes...
New:
config ARCH_SUPPORTS_KEXEC
def_bool y

config ARCH_SUPPORTS_KEXEC_FILE
def_bool X86_64 && CRYPTO && CRYPTO_SHA256

config ARCH_SELECTS_KEXEC_FILE
def_bool y
depends on KEXEC_FILE
select HAVE_IMA_KEXEC if IMA

config ARCH_HAS_KEXEC_PURGATORY
def_bool KEXEC_FILE

config ARCH_SUPPORTS_KEXEC_JUMP
def_bool y

config ARCH_SUPPORTS_CRASH_DUMP
def_bool X86_64 || (X86_32 && HIGHMEM)

===== powerpc (minus the help section) =====
Original:
config KEXEC
bool "kexec system call"
depends on PPC_BOOK3S || PPC_E500 || (44x && !SMP)
select KEXEC_CORE

config KEXEC_FILE
bool "kexec file based system call"
select KEXEC_CORE
select HAVE_IMA_KEXEC if IMA
select KEXEC_ELF
depends on PPC64
depends on CRYPTO=y
depends on CRYPTO_SHA256=y

config ARCH_HAS_KEXEC_PURGATORY
def_bool KEXEC_FILE

config CRASH_DUMP
bool "Build a dump capture kernel"
depends on PPC64 || PPC_BOOK3S_32 || PPC_85xx || (44x && !SMP)
select RELOCATABLE if PPC64 || 44x || PPC_85xx

becomes...
New:
config ARCH_SUPPORTS_KEXEC
def_bool PPC_BOOK3S || PPC_E500 || (44x && !SMP)

config ARCH_SUPPORTS_KEXEC_FILE
def_bool PPC64 && CRYPTO=y && CRYPTO_SHA256=y

config ARCH_HAS_KEXEC_PURGATORY
def_bool KEXEC_FILE

config ARCH_SELECTS_KEXEC_FILE
def_bool y
depends on KEXEC_FILE
select KEXEC_ELF
select HAVE_IMA_KEXEC if IMA

config ARCH_SUPPORTS_CRASH_DUMP
def_bool PPC64 || PPC_BOOK3S_32 || PPC_85xx || (44x && !SMP)

config ARCH_SELECTS_CRASH_DUMP
def_bool y
depends on CRASH_DUMP
select RELOCATABLE if PPC64 || 44x || PPC_85xx

Testing Approach and Results

There are 388 config files in the arch/<arch>/configs directories.
For each of these config files, a .config is generated both before and
after this Kconfig series, and checked for equivalence. This approach
allows for a rather rapid check of all architectures and a wide
variety of configs wrt/ KEXEC and CRASH, and avoids requiring
compiling for all architectures and running kernels and run-time
testing.

As such, I developed the following script to compare the before and
after of 'make olddefconfig'. The new symbols introduced by this
series are filtered out, but otherwise the config files are PASS
only if they were equivalent, and FAIL otherwise.

The script performs the test by doing the following:

# Obtain the "golden" .config output for given config file
# Reset test sandbox
git checkout master
git branch -D test_Kconfig
git checkout -B test_Kconfig master
make distclean
# Write out updated config
cp -f <config file> .config
make ARCH=<arch> olddefconfig
# Track each item in .config, LHSB is "golden"
scoreboard .config

# Obtain the "changed" .config output for given config file
# Reset test sandbox
make distclean
# Apply this Kconfig series
git am <this Kconfig series>
# Write out updated config
cp -f <config file> .config
make ARCH=<arch> olddefconfig
# Track each item in .config, RHSB is "changed"
scoreboard .config

# Determine test result
# Filter-out new symbols introduced by this series
# Filter-out symbol=n which not in either scoreboard
# Compare LHSB "golden" and RHSB "changed" scoreboards and issue PASS/FAIL

The script was instrumental during the refactoring of Kconfig as it
continually revealed problems. The end result being that the solution
presented in this series passes all configs as checked by the script.

Regards,
eric

---
v2: 19jun2023
- The ARCH_HAS_ and ARCH_SUPPORTS_ combination was found to be
too similar. Renamed these two new options as such:
ARCH_HAS_ ---> ARCH_SUPPORTS_
ARCH_SUPPORTS_ ---> ARCH_SELECTS_
Per Kees Cook, Michael Ellerman
NOTE: ARCH_HAS_KEXEC_PURGATORY was left as-is, as that is what
it is prior to this series.
Updated this cover letter to reflect the same.
- Some minor cleaning up of the help sections, per Zhen Lei and
Alexander Gordeev.
- Removed the MODULE_SIG_FORMAT dependency from KEXEC_SIG in
kernel/Kconfig.kexec. Only s390 had it prior to this series.
See also commit message in
"s390/kexec: refactor for kernel/Kconfig.kexec"
- Added to Kconfig.kexec the KEXEC_IMAGE_VERIFY_SIG from arm64,
per Zhen Lei.
- Fixed the powerpc ARCH_SUPPORTS_KEXEC_FILE conversion, per
Michael Ellerman.

v1: 12jun2023
https://lore.kernel.org/lkml/20230612172805.681179-1-eric.devolder@oracle.com/
- Initial
- Based on 6.4.0-rc6

---

Eric DeVolder (13):
kexec: consolidate kexec and crash options into kernel/Kconfig.kexec
x86/kexec: refactor for kernel/Kconfig.kexec
arm/kexec: refactor for kernel/Kconfig.kexec
ia64/kexec: refactor for kernel/Kconfig.kexec
arm64/kexec: refactor for kernel/Kconfig.kexec
loongarch/kexec: refactor for kernel/Kconfig.kexec
m68k/kexec: refactor for kernel/Kconfig.kexec
mips/kexec: refactor for kernel/Kconfig.kexec
parisc/kexec: refactor for kernel/Kconfig.kexec
powerpc/kexec: refactor for kernel/Kconfig.kexec
riscv/kexec: refactor for kernel/Kconfig.kexec
s390/kexec: refactor for kernel/Kconfig.kexec
sh/kexec: refactor for kernel/Kconfig.kexec

arch/Kconfig | 13 -----
arch/arm/Kconfig | 29 ++---------
arch/arm64/Kconfig | 62 +++++------------------
arch/ia64/Kconfig | 28 ++---------
arch/loongarch/Kconfig | 26 +++-------
arch/m68k/Kconfig | 19 +------
arch/mips/Kconfig | 32 ++----------
arch/parisc/Kconfig | 34 +++++--------
arch/powerpc/Kconfig | 55 +++++++--------------
arch/riscv/Kconfig | 48 ++++++------------
arch/s390/Kconfig | 65 +++++++-----------------
arch/sh/Kconfig | 46 +++--------------
arch/x86/Kconfig | 89 +++++----------------------------
init/Kconfig | 2 +
kernel/Kconfig.kexec | 110 +++++++++++++++++++++++++++++++++++++++++
15 files changed, 229 insertions(+), 429 deletions(-)
create mode 100644 kernel/Kconfig.kexec

--
2.31.1