[PATCH v3 00/12] kasan: unify kasan_arch_is_ready() and remove arch-specific implementations

[Sabyrzhan Tasbolatov <snovitoll@gmail.com>]

This patch series addresses the fragmentation in KASAN initialization
across architectures by introducing a unified approach that eliminates
duplicate static keys and arch-specific kasan_arch_is_ready()
implementations.

The core issue is that different architectures have inconsistent approaches
to KASAN readiness tracking:
- PowerPC, LoongArch, and um arch, each implement own kasan_arch_is_ready()
- Only HW_TAGS mode had a unified static key (kasan_flag_enabled)
- Generic and SW_TAGS modes relied on arch-specific solutions
  or always-on behavior

This series implements two-level approach:
1. kasan_enabled() - compile-time check for KASAN configuration
2. kasan_shadow_initialized() - runtime check for shadow memory readiness

Key improvements:
- Unified static key infrastructure across all KASAN modes
- Runtime overhead only for architectures that actually need it
- Compile-time optimization for arch. with early KASAN initialization
- Complete elimination of arch-specific kasan_arch_is_ready()
- Consistent interface and reduced code duplication

Previous v2 thread: https://lore.kernel.org/all/20250626153147.145312-1-snovitoll@gmail.com/

Changes in v3 (sorry for the 3-week gap):

0. Included in TO, CC only KASAN devs and people who commented in v2.

1. Addressed Andrey Konovalov's feedback:
   - Kept separate kasan_enabled() and kasan_shadow_initialized() functions
   - Added proper __wrapper functions with clean separation

2. Addressed Christophe Leroy's performance comments:
   - CONFIG_ARCH_DEFER_KASAN is only selected by architectures that need it
   - No static key overhead for architectures that can enable KASAN early
   - PowerPC 32-bit and book3e get compile-time optimization

3. Addressed Heiko Carstens and Alexander Gordeev s390 comments:
   - s390 doesn't select ARCH_DEFER_KASAN (no unnecessary static key overhead)
   - kasan_enable() is a no-op for architectures with early KASAN setup

4. Improved wrapper architecture:
   - All existing wrapper functions in include/linux/kasan.h now check both
     kasan_enabled() && kasan_shadow_initialized()
   - Internal implementation functions focus purely on core functionality
   - Shadow readiness logic is centralized in headers per Andrey's guidance

Architecture-specific changes:
- PowerPC radix MMU: selects ARCH_DEFER_KASAN for runtime control
- LoongArch: selects ARCH_DEFER_KASAN, removes custom kasan_early_stage
- um: selects ARCH_DEFER_KASAN, removes kasan_um_is_ready
- Other architectures: get compile-time optimization, no runtime overhead

The series maintains full backward compatibility while providing optimal
performance for each architecture's needs.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049

=== Current mainline KUnit status

To see if there is any regression, I've tested via compiling a kernel
with CONFIG_KASAN_KUNIT_TEST and running QEMU VM. There are failing tests
in SW_TAGS and GENERIC modes in arm64:

arm64 CONFIG_KASAN_HW_TAGS:
	# kasan: pass:62 fail:0 skip:13 total:75
	# Totals: pass:62 fail:0 skip:13 total:75
	ok 1 kasan

arm64 CONFIG_KASAN_SW_TAGS=y:
	# kasan: pass:65 fail:1 skip:9 total:75
	# Totals: pass:65 fail:1 skip:9 total:75
	not ok 1 kasan
	# kasan_strings: EXPECTATION FAILED at mm/kasan/kasan_test_c.c:1598
	KASAN failure expected in "strscpy(ptr, src + KASAN_GRANULE_SIZE, KASAN_GRANULE_SIZE)", but none occurred

arm64 CONFIG_KASAN_GENERIC=y, CONFIG_KASAN_OUTLINE=y:
	# kasan: pass:61 fail:1 skip:13 total:75
	# Totals: pass:61 fail:1 skip:13 total:75
	not ok 1 kasan
	# same failure as above

x86_64 CONFIG_KASAN_GENERIC=y:
	# kasan: pass:58 fail:0 skip:17 total:75
	# Totals: pass:58 fail:0 skip:17 total:75
	ok 1 kasan

=== Testing with patches

Testing in v3:

- Compiled every affected arch with no errors:

$ make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \
	OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \
	HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld \
	ARCH=$ARCH

$ clang --version
ClangBuiltLinux clang version 19.1.4
Target: x86_64-unknown-linux-gnu
Thread model: posix

- make ARCH=um produces the warning during compiling:
	MODPOST Module.symvers
	WARNING: modpost: vmlinux: section mismatch in reference: \
		kasan_init+0x43 (section: .ltext) -> \
		kasan_init_generic (section: .init.text)

AFAIU, it's due to the code in arch/um/kernel/mem.c, where kasan_init()
is placed in own section ".kasan_init", which calls kasan_init_generic()
which is marked with "__init".

- Booting via qemu-system- and running KUnit tests:

* arm64  (GENERIC, HW_TAGS, SW_TAGS): no regression, same above results.
* x86_64 (GENERIC): no regression, no errors

Sabyrzhan Tasbolatov (12):
  lib/kasan: introduce CONFIG_ARCH_DEFER_KASAN option
  kasan: unify static kasan_flag_enabled across modes
  kasan/powerpc: select ARCH_DEFER_KASAN and call kasan_init_generic
  kasan/arm64: call kasan_init_generic in kasan_init
  kasan/arm: call kasan_init_generic in kasan_init
  kasan/xtensa: call kasan_init_generic in kasan_init
  kasan/loongarch: select ARCH_DEFER_KASAN and call kasan_init_generic
  kasan/um: select ARCH_DEFER_KASAN and call kasan_init_generic
  kasan/x86: call kasan_init_generic in kasan_init
  kasan/s390: call kasan_init_generic in kasan_init
  kasan/riscv: call kasan_init_generic in kasan_init
  kasan: add shadow checks to wrappers and rename kasan_arch_is_ready

 arch/arm/mm/kasan_init.c               |  2 +-
 arch/arm64/mm/kasan_init.c             |  4 +--
 arch/loongarch/Kconfig                 |  1 +
 arch/loongarch/include/asm/kasan.h     |  7 -----
 arch/loongarch/mm/kasan_init.c         |  7 ++---
 arch/powerpc/Kconfig                   |  1 +
 arch/powerpc/include/asm/kasan.h       | 12 --------
 arch/powerpc/mm/kasan/init_32.c        |  2 +-
 arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
 arch/powerpc/mm/kasan/init_book3s_64.c |  6 +---
 arch/riscv/mm/kasan_init.c             |  1 +
 arch/s390/kernel/early.c               |  3 +-
 arch/um/Kconfig                        |  1 +
 arch/um/include/asm/kasan.h            |  5 ---
 arch/um/kernel/mem.c                   |  4 +--
 arch/x86/mm/kasan_init_64.c            |  2 +-
 arch/xtensa/mm/kasan_init.c            |  2 +-
 include/linux/kasan-enabled.h          | 34 ++++++++++++++++-----
 include/linux/kasan.h                  | 42 ++++++++++++++++++++------
 lib/Kconfig.kasan                      |  8 +++++
 mm/kasan/common.c                      | 18 +++++++----
 mm/kasan/generic.c                     | 23 ++++++++------
 mm/kasan/hw_tags.c                     |  9 +-----
 mm/kasan/kasan.h                       | 36 ++++++++++++++++------
 mm/kasan/shadow.c                      | 32 +++++---------------
 mm/kasan/sw_tags.c                     |  2 ++
 26 files changed, 146 insertions(+), 120 deletions(-)

-- 
2.34.1