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-snovit...@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
