Le 26/06/2025 à 17:31, Sabyrzhan Tasbolatov a écrit :

This patch series unifies the kasan_arch_is_ready() and kasan_enabled()
interfaces by extending the existing kasan_enabled() infrastructure to
work consistently across all KASAN modes (Generic, SW_TAGS, HW_TAGS).

Currently, kasan_enabled() only works for HW_TAGS mode using a static key,
while other modes either return IS_ENABLED(CONFIG_KASAN) (compile-time
constant) or rely on architecture-specific kasan_arch_is_ready()
implementations with custom static keys and global variables.

This leads to:
- Code duplication across architectures
- Inconsistent runtime behavior between KASAN modes
- Architecture-specific readiness tracking

You should also consider refactoring ARCH_DISABLE_KASAN_INLINE, there is 
a high dependency between deferring KASAN readiness and not supporting 
inline KASAN.

After this series:
- All KASAN modes use the same kasan_flag_enabled static key
- Consistent runtime enable/disable behavior across modes
- Simplified architecture code with unified kasan_init_generic() calls
- Elimination of arch specific kasan_arch_is_ready() implementations
- Unified vmalloc integration using kasan_enabled() checks

I dislike that modes which can be enabled from the very begining now 
also depends on the static key being enabled later.

The size is increased for no valid reason:

$ size vmlinux.kasan*
    text	   data	    bss	    dec	    hex	filename
13965336	6716942	 494912	21177190	1432366	vmlinux.kasan0 ==> outline 
KASAN before your patch
13965496	6718422	 494944	21178862	14329ee	vmlinux.kasan1 ==> outline 
KASAN after your patch
13965336	6716942	 494912	21177190	1432366	vmlinux.kasan2 ==> outline 
KASAN after your patch + below change
32517472	6716958	 494912	39729342	25e38be	vmlinux.kasani0 ==> inline 
KASAN before your patch
32518848	6718438	 494944	39732230	25e4406	vmlinux.kasani1 ==> inline 
KASAN after your patch
32517536	6716958	 494912	39729406	25e38fe	vmlinux.kasani2 ==> inline 
KASAN after your patch + below change

Below change (atop you series) only makes use of static key when needed:

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c3e0cc83f120..7a8e5db603cc 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -122,6 +122,7 @@ config PPC
  	# Please keep this list sorted alphabetically.
  	#
  	select ARCH_32BIT_OFF_T if PPC32
+	select ARCH_DEFER_KASAN			if PPC_RADIX_MMU
  	select ARCH_DISABLE_KASAN_INLINE	if PPC_RADIX_MMU
  	select ARCH_DMA_DEFAULT_COHERENT	if !NOT_COHERENT_CACHE
  	select ARCH_ENABLE_MEMORY_HOTPLUG

@@ -219,7 +220,7 @@ config PPC
  	select HAVE_ARCH_JUMP_LABEL
  	select HAVE_ARCH_JUMP_LABEL_RELATIVE
  	select HAVE_ARCH_KASAN			if PPC32 && PAGE_SHIFT <= 14
-	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU
+	select HAVE_ARCH_KASAN_DEFERED		if PPC_RADIX_MMU
  	select HAVE_ARCH_KASAN			if PPC_BOOK3E_64
  	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
  	select HAVE_ARCH_KCSAN

diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
index 2436eb45cfee..fda86e77fe4f 100644
--- a/include/linux/kasan-enabled.h
+++ b/include/linux/kasan-enabled.h

@@ -4,7 +4,7 @@

  #include <linux/static_key.h>

-#ifdef CONFIG_KASAN
+#ifdef CONFIG_KASAN_DEFER

  /*
   * Global runtime flag. Starts ‘false’; switched to ‘true’ by

@@ -17,13 +17,21 @@ static __always_inline bool kasan_enabled(void)
  	return static_branch_likely(&kasan_flag_enabled);
  }

-#else /* !CONFIG_KASAN */
+static inline void kasan_enable(void)
+{
+	static_branch_enable(&kasan_flag_enabled);
+}
+
+#else /* !CONFIG_KASAN_DEFER */

  static __always_inline bool kasan_enabled(void)
  {
-	return false;
+	return IS_ENABLED(CONFIG_KASAN);
  }

+static inline void kasan_enable(void)
+{
+}
  #endif /* CONFIG_KASAN */

  #ifdef CONFIG_KASAN_HW_TAGS

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index f82889a830fa..e0c300f55c07 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan

@@ -13,6 +13,9 @@ config HAVE_ARCH_KASAN_HW_TAGS
  config HAVE_ARCH_KASAN_VMALLOC
  	bool

+config ARCH_DEFER_KASAN
+	bool
+
  config ARCH_DISABLE_KASAN_INLINE
  	bool
  	help

@@ -58,6 +61,9 @@ config CC_HAS_KASAN_MEMINTRINSIC_PREFIX
  	help
  	  The compiler is able to prefix memintrinsics with __asan or __hwasan.

+config KASAN_DIFER
+	def_bool ARCH_DIFER_KASAN
+
  choice
  	prompt "KASAN mode"
  	default KASAN_GENERIC

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 0f3648335a6b..01f56eed9d20 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c

@@ -36,8 +36,10 @@
   * Definition of the unified static key declared in kasan-enabled.h.
   * This provides consistent runtime enable/disable across all KASAN modes.
   */
+#ifdef CONFIG_KASAN_DEFER
  DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
  EXPORT_SYMBOL(kasan_flag_enabled);
+#endif

  struct slab *kasan_addr_to_slab(const void *addr)
  {

diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index a3b112868be7..516b49accc4f 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c

@@ -42,7 +42,7 @@
   */
  void __init kasan_init_generic(void)
  {
-	static_branch_enable(&kasan_flag_enabled);
+	kasan_enable();

  	pr_info("KernelAddressSanitizer initialized (generic)\n");
  }

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 8e819fc4a260..c8289a3feabf 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c

@@ -253,7 +253,7 @@ void __init kasan_init_hw_tags(void)
  	kasan_init_tags();

  	/* KASAN is now initialized, enable it. */
-	static_branch_enable(&kasan_flag_enabled);
+	kasan_enable();

  	pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, 

vmalloc=%s, stacktrace=%s)\n",
  		kasan_mode_info(),

diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
index 525bc91e2fcd..275bcbbf6120 100644
--- a/mm/kasan/sw_tags.c
+++ b/mm/kasan/sw_tags.c

@@ -45,7 +45,7 @@ void __init kasan_init_sw_tags(void)

  	kasan_init_tags();

-	static_branch_enable(&kasan_flag_enabled);
+	kasan_enable();

  	pr_info("KernelAddressSanitizer initialized (sw-tags, stacktrace=%s)\n",
  		str_on_off(kasan_stack_collection_enabled()));

This addresses the bugzilla issue [1] about making
kasan_flag_enabled and kasan_enabled() work for Generic mode,
and extends it to provide true unification across all modes.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=217049

=== Current mainline KUnit status

To see if there is any regression, I've tested first on the following
commit 739a6c93cc75 ("Merge tag 'nfsd-6.16-1' of
git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux").

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 v2:

- 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

=== NB

I haven't tested the kernel boot on the following arch. due to the absence
of qemu-system- support on those arch on my machine, so I defer this to
relevant arch people to test KASAN initialization:
- loongarch
- s390
- um
- xtensa
- powerpc
- riscv

Code changes in v2:
- Replace the order of patches. Move "kasan: replace kasan_arch_is_ready
	with kasan_enabled" at the end to keep the compatibility.
- arch/arm, arch/riscv: add 2 arch. missed in v1
- arch/powerpc: add kasan_init_generic() in other kasan_init() calls:
	arch/powerpc/mm/kasan/init_32.c
	arch/powerpc/mm/kasan/init_book3e_64.c
- arch/um: add the proper header `#include <linux/kasan.h>`. Tested
	via compiling with no errors. In the v1 arch/um changes were acked-by
	Johannes Berg, though I don't include it due to the changed code in v2.
- arch/powerpc: add back `#ifdef CONFIG_KASAN` deleted in v1 and tested
	the compilation.
- arch/loongarch: update git commit message about non-standard flow of
	calling kasan_init_generic()

Sabyrzhan Tasbolatov (11):
   kasan: unify static kasan_flag_enabled across modes
   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: call kasan_init_generic in kasan_init
   kasan/um: call kasan_init_generic in kasan_init
   kasan/x86: call kasan_init_generic in kasan_init
   kasan/s390: call kasan_init_generic in kasan_init
   kasan/powerpc: call kasan_init_generic in kasan_init
   kasan/riscv: call kasan_init_generic in kasan_init
   kasan: replace kasan_arch_is_ready with kasan_enabled

  arch/arm/mm/kasan_init.c               |  2 +-
  arch/arm64/mm/kasan_init.c             |  4 +---
  arch/loongarch/include/asm/kasan.h     |  7 -------
  arch/loongarch/mm/kasan_init.c         |  7 ++-----
  arch/powerpc/include/asm/kasan.h       | 13 -------------
  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/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          | 22 ++++++++++++++++------
  include/linux/kasan.h                  |  6 ++++++
  mm/kasan/common.c                      | 15 +++++++++++----
  mm/kasan/generic.c                     | 17 ++++++++++++++---
  mm/kasan/hw_tags.c                     |  7 -------
  mm/kasan/kasan.h                       |  6 ------
  mm/kasan/shadow.c                      | 15 +++------------
  mm/kasan/sw_tags.c                     |  2 ++
  22 files changed, 66 insertions(+), 84 deletions(-)