[PATCH V3] powerpc/kasan: require memintrinsic prefix support for KASAN

[PATCH V3] powerpc/kasan: require memintrinsic prefix support for KASAN

[Mukesh Kumar Chaurasiya (IBM)]

powerpc unconditionally selects GENERIC_ENTRY. The GENERIC_ENTRY
infrastructure relies on the compiler emitting __asan_mem*() calls at
instrumented mem*() sites rather than plain memset/memcpy/memmove, so
that entry/exit paths calling those functions are not instrumented.

This assumption is encoded in two places:

  mm/kasan/shadow.c:
    #if !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX) &&
        !defined(CONFIG_GENERIC_ENTRY)

  include/linux/fortify-string.h:
    #if !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX) &&
        !defined(CONFIG_GENERIC_ENTRY)

When GENERIC_ENTRY is set, both guards suppress the C wrappers for
memset/memcpy/memmove and the __underlying_mem*() redirections. This
is only safe when the compiler supports the prefixed __asan_mem*()
intrinsics. On older toolchains (e.g. GCC 9) that lack this support,
plain mem*() calls from instrumented code fall through to the raw
assembly implementations in mem_64.S / copy_32.S, completely bypassing
the KASAN shadow check.

Other arches with GENERIC_ENTRY (x86, s390, loongarch, riscv) do not
hit this because their CI toolchains are always new enough to support
the prefix flag.

Background: the !GENERIC_ENTRY guard was introduced by commit 69d4c0d32186
("entry, kasan, x86: Disallow overriding mem*() functions", Peter Zijlstra,
Jan 2023). The root problem is that the KASAN C wrappers override the
linker symbol memset/memcpy/memmove globally, so any call from noinstr or
__no_sanitize_address code (e.g. irqentry_enter/irqentry_exit) would still
reach the KASAN shadow-check wrapper -- at a point where KASAN invariants
may not hold. The compiler prefix approach (Marco Elver, Feb 2023,
commit 51287dcb00cc) solves this by having the compiler emit __asan_memset
at instrumented call sites and bare memset inside __no_sanitize_address
functions, splitting the decision at code-generation time rather than at
link time.

A manual C-level override cannot replicate this split: a single linker
symbol cannot be made to resolve differently depending on the caller.

x86 also placed its raw memset/memcpy/memmove implementations in
.noinstr.text (same commit, 69d4c0d32186), which is the other half of
the fix: noinstr callers hit the raw assembly directly, safely bypassing
KASAN. PowerPC has not done this. Placing mem_64.S / memcpy_64.S /
copy_32.S implementations in .noinstr.text would be the complementary
long-term fix that could re-enable KASAN on older toolchains, but it
requires care around linker stub overflow on large PPC64 kernels (the
same reason powerpc uses NOKPROBE_SYMBOL rather than noinstr for its
interrupt handlers -- see the comment in asm/interrupt.h). That work
is left as a follow-up.

For now, introduce PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX, an arch-local
compiler probe that mirrors the same check as CC_HAS_KASAN_MEMINTRINSIC_PREFIX
in lib/Kconfig.kasan but lives outside the 'if KASAN' block to avoid a
recursive dependency (CC_HAS_KASAN_MEMINTRINSIC_PREFIX depends on KASAN
which depends on HAVE_ARCH_KASAN). Gate the three HAVE_ARCH_KASAN selects
on this new symbol so that KASAN is not offered as a config option on
toolchains that cannot support it correctly with GENERIC_ENTRY.

Since KASAN on powerpc now unconditionally implies
CC_HAS_KASAN_MEMINTRINSIC_PREFIX, the old !CC_HAS_KASAN_MEMINTRINSIC_PREFIX
code paths in asm/kasan.h and asm/string.h are dead. Clean them up:

- asm/kasan.h: remove the dual-entry-point variant of _GLOBAL_KASAN /
  _GLOBAL_TOC_KASAN / EXPORT_SYMBOL_KASAN that emitted both memset and
  __memset as entry points to the same assembly. These aliases were only
  needed so the C KASAN wrappers in shadow.c could call __memset() to
  reach raw memory ops; with the compiler prefix approach those wrappers
  are not used for mem* on powerpc.

- asm/string.h: remove the separate __memset/__memcpy/__memmove symbol
  declarations and the memset/memcpy/memmove macro redirections for
  uninstrumented files that were needed on old toolchains. Simplify the
  CONFIG_KASAN block to just the three #define aliases (still used by
  shadow.c as raw backends to bypass KASAN checking).

- cputable.c, prom_init.c: the memcpy is not required now as the manual
  instrumentation of memcpy is removed. Hence directly use *dest = *src
  for this.

Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Closes: https://lore.kernel.org/all/96dae110-f79b-4e54-8a9b-514369019b5d@linux.ibm.com
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
---
Changelog:
V2 -> V3:
- *dest = *src used instead of memcpy in cputable.c and prom_init.c
V2: https://lore.kernel.org/all/20260911180536.3234640-2-mkchauras@gmail.com

V1 -> V2:
- Comments reworded
- Commit message reworded
V1: https://lore.kernel.org/all/20260908064948.999530-1-mkchauras@gmail.com

 arch/powerpc/Kconfig              | 10 +++++++---
 arch/powerpc/include/asm/kasan.h  | 11 -----------
 arch/powerpc/include/asm/string.h | 21 +--------------------
 arch/powerpc/kernel/cputable.c    | 14 ++------------
 arch/powerpc/kernel/prom_init.c   | 10 ++--------
 5 files changed, 12 insertions(+), 54 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2580e27e4328..b27ed9739eea 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -7,6 +7,10 @@ config CC_HAS_ELFV2
 config CC_HAS_PREFIXED
 	def_bool PPC64 && $(cc-option, -mcpu=power10 -mprefixed)
 
+config PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=kernel-address -mllvm -asan-kernel-mem-intrinsic-prefix=1)) || \
+		 (CC_IS_GCC && $(cc-option,-fsanitize=kernel-address --param asan-kernel-mem-intrinsic-prefix=1))
+
 config CC_HAS_PCREL
 	# Clang has a bug (https://github.com/llvm/llvm-project/issues/62372)
 	# where pcrel code is not generated if -msoft-float, -mno-altivec, or
@@ -220,9 +224,9 @@ config PPC
 	select HAVE_ARCH_HUGE_VMAP		if PPC_RADIX_MMU || PPC_8xx
 	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			if PPC_BOOK3E_64
+	select HAVE_ARCH_KASAN			if PPC32 && PAGE_SHIFT <= 14 && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+	select HAVE_ARCH_KASAN			if PPC_BOOK3E_64 && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
 	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
 	select HAVE_ARCH_KCSAN
 	select HAVE_ARCH_KFENCE			if ARCH_SUPPORTS_DEBUG_PAGEALLOC
diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
index a690e7da53c2..d62756b87ba4 100644
--- a/arch/powerpc/include/asm/kasan.h
+++ b/arch/powerpc/include/asm/kasan.h
@@ -2,20 +2,9 @@
 #ifndef __ASM_KASAN_H
 #define __ASM_KASAN_H
 
-#if defined(CONFIG_KASAN) && !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX)
-#define _GLOBAL_KASAN(fn)			\
-	_GLOBAL(fn);				\
-	_GLOBAL(__##fn)
-#define _GLOBAL_TOC_KASAN(fn)			\
-	_GLOBAL_TOC(fn);			\
-	_GLOBAL_TOC(__##fn)
-#define EXPORT_SYMBOL_KASAN(fn)			\
-	EXPORT_SYMBOL(__##fn)
-#else /* CONFIG_KASAN && !CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
 #define _GLOBAL_KASAN(fn)	_GLOBAL(fn)
 #define _GLOBAL_TOC_KASAN(fn)	_GLOBAL_TOC(fn)
 #define EXPORT_SYMBOL_KASAN(fn)
-#endif /* CONFIG_KASAN && !CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
 
 #ifndef __ASSEMBLER__
 
diff --git a/arch/powerpc/include/asm/string.h b/arch/powerpc/include/asm/string.h
index 1981bd4036b5..72b5c93a2b84 100644
--- a/arch/powerpc/include/asm/string.h
+++ b/arch/powerpc/include/asm/string.h
@@ -29,29 +29,10 @@ extern void * memchr(const void *,int,__kernel_size_t);
 void memcpy_flushcache(void *dest, const void *src, size_t size);
 
 #ifdef CONFIG_KASAN
-/* __mem variants are used by KASAN to implement instrumented meminstrinsics. */
-#ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+/* Used by mm/kasan/shadow.c as raw backends to bypass KASAN checking. */
 #define __memset memset
 #define __memcpy memcpy
 #define __memmove memmove
-#else /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
-void *__memset(void *s, int c, __kernel_size_t count);
-void *__memcpy(void *to, const void *from, __kernel_size_t n);
-void *__memmove(void *to, const void *from, __kernel_size_t n);
-#ifndef __SANITIZE_ADDRESS__
-/*
- * For files that are not instrumented (e.g. mm/slub.c) we
- * should use not instrumented version of mem* functions.
- */
-#define memcpy(dst, src, len) __memcpy(dst, src, len)
-#define memmove(dst, src, len) __memmove(dst, src, len)
-#define memset(s, c, n) __memset(s, c, n)
-
-#ifndef __NO_FORTIFY
-#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
-#endif
-#endif /* !__SANITIZE_ADDRESS__ */
-#endif /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
 #endif /* CONFIG_KASAN */
 
 #ifdef CONFIG_PPC64
diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index 6f6801da9dc1..6356b5c6be7b 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -35,12 +35,7 @@ void __init set_cur_cpu_spec(struct cpu_spec *s)
 	struct cpu_spec *t = &the_cpu_spec;
 
 	t = PTRRELOC(t);
-	/*
-	 * use memcpy() instead of *t = *s so that GCC replaces it
-	 * by __memcpy() when KASAN is active
-	 */
-	memcpy(t, s, sizeof(*t));
-
+	*t = *s;
 	*PTRRELOC(&cur_cpu_spec) = &the_cpu_spec;
 }
 
@@ -52,12 +47,7 @@ static struct cpu_spec * __init setup_cpu_spec(unsigned long offset,
 
 	t = PTRRELOC(t);
 	old = *t;
-
-	/*
-	 * Copy everything, then do fixups. Use memcpy() instead of *t = *s
-	 * so that GCC replaces it by __memcpy() when KASAN is active
-	 */
-	memcpy(t, s, sizeof(*t));
+	*t = *s;
 
 	/*
 	 * If we are overriding a previous value derived from the real
diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index eb9f556b0937..e8e071024da5 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -1362,14 +1362,8 @@ static void __init prom_check_platform_support(void)
 	int prop_len = prom_getproplen(prom.chosen,
 				       "ibm,arch-vec-5-platform-support");
 
-	/*
-	 * First copy the architecture vec template
-	 *
-	 * use memcpy() instead of *vec = *vec_template so that GCC replaces it
-	 * by __memcpy() when KASAN is active
-	 */
-	memcpy(&ibm_architecture_vec, &ibm_architecture_vec_template,
-	       sizeof(ibm_architecture_vec));
+	/* First copy the architecture vec template */
+	ibm_architecture_vec = ibm_architecture_vec_template;
 
 	prom_strscpy_pad(ibm_architecture_vec.vec7.os_id, linux_banner, 256);
 
-- 
2.55.0

Re: [PATCH V3] powerpc/kasan: require memintrinsic prefix support for KASAN

[Christophe Leroy (CS GROUP)]

Le 15/09/2026 à 12:09, Mukesh Kumar Chaurasiya (IBM) a écrit :
> powerpc unconditionally selects GENERIC_ENTRY. The GENERIC_ENTRY
> infrastructure relies on the compiler emitting __asan_mem*() calls at
> instrumented mem*() sites rather than plain memset/memcpy/memmove, so
> that entry/exit paths calling those functions are not instrumented.
> 
> This assumption is encoded in two places:
> 
>    mm/kasan/shadow.c:
>      #if !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX) &&
>          !defined(CONFIG_GENERIC_ENTRY)
> 
>    include/linux/fortify-string.h:
>      #if !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX) &&
>          !defined(CONFIG_GENERIC_ENTRY)
> 
> When GENERIC_ENTRY is set, both guards suppress the C wrappers for
> memset/memcpy/memmove and the __underlying_mem*() redirections. This
> is only safe when the compiler supports the prefixed __asan_mem*()
> intrinsics. On older toolchains (e.g. GCC 9) that lack this support,
> plain mem*() calls from instrumented code fall through to the raw
> assembly implementations in mem_64.S / copy_32.S, completely bypassing
> the KASAN shadow check.
> 
> Other arches with GENERIC_ENTRY (x86, s390, loongarch, riscv) do not
> hit this because their CI toolchains are always new enough to support
> the prefix flag.
> 
> Background: the !GENERIC_ENTRY guard was introduced by commit 69d4c0d32186
> ("entry, kasan, x86: Disallow overriding mem*() functions", Peter Zijlstra,
> Jan 2023). The root problem is that the KASAN C wrappers override the
> linker symbol memset/memcpy/memmove globally, so any call from noinstr or
> __no_sanitize_address code (e.g. irqentry_enter/irqentry_exit) would still
> reach the KASAN shadow-check wrapper -- at a point where KASAN invariants
> may not hold. The compiler prefix approach (Marco Elver, Feb 2023,
> commit 51287dcb00cc) solves this by having the compiler emit __asan_memset
> at instrumented call sites and bare memset inside __no_sanitize_address
> functions, splitting the decision at code-generation time rather than at
> link time.
> 
> A manual C-level override cannot replicate this split: a single linker
> symbol cannot be made to resolve differently depending on the caller.
> 
> x86 also placed its raw memset/memcpy/memmove implementations in
> .noinstr.text (same commit, 69d4c0d32186), which is the other half of
> the fix: noinstr callers hit the raw assembly directly, safely bypassing
> KASAN. PowerPC has not done this. Placing mem_64.S / memcpy_64.S /
> copy_32.S implementations in .noinstr.text would be the complementary
> long-term fix that could re-enable KASAN on older toolchains, but it
> requires care around linker stub overflow on large PPC64 kernels (the
> same reason powerpc uses NOKPROBE_SYMBOL rather than noinstr for its
> interrupt handlers -- see the comment in asm/interrupt.h). That work
> is left as a follow-up.
> 
> For now, introduce PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX, an arch-local
> compiler probe that mirrors the same check as CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> in lib/Kconfig.kasan but lives outside the 'if KASAN' block to avoid a
> recursive dependency (CC_HAS_KASAN_MEMINTRINSIC_PREFIX depends on KASAN
> which depends on HAVE_ARCH_KASAN). Gate the three HAVE_ARCH_KASAN selects
> on this new symbol so that KASAN is not offered as a config option on
> toolchains that cannot support it correctly with GENERIC_ENTRY.
> 
> Since KASAN on powerpc now unconditionally implies
> CC_HAS_KASAN_MEMINTRINSIC_PREFIX, the old !CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> code paths in asm/kasan.h and asm/string.h are dead. Clean them up:
> 
> - asm/kasan.h: remove the dual-entry-point variant of _GLOBAL_KASAN /
>    _GLOBAL_TOC_KASAN / EXPORT_SYMBOL_KASAN that emitted both memset and
>    __memset as entry points to the same assembly. These aliases were only
>    needed so the C KASAN wrappers in shadow.c could call __memset() to
>    reach raw memory ops; with the compiler prefix approach those wrappers
>    are not used for mem* on powerpc.
> 
> - asm/string.h: remove the separate __memset/__memcpy/__memmove symbol
>    declarations and the memset/memcpy/memmove macro redirections for
>    uninstrumented files that were needed on old toolchains. Simplify the
>    CONFIG_KASAN block to just the three #define aliases (still used by
>    shadow.c as raw backends to bypass KASAN checking).
> 
> - cputable.c, prom_init.c: the memcpy is not required now as the manual
>    instrumentation of memcpy is removed. Hence directly use *dest = *src
>    for this.
> 
> Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
> Closes: https://lore.kernel.org/all/96dae110-f79b-4e54-8a9b-514369019b5d@linux.ibm.com
> Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>

Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>

> ---
> Changelog:
> V2 -> V3:
> - *dest = *src used instead of memcpy in cputable.c and prom_init.c

We could have left the memcpy() there but I'm fine either way. What was 
important was to remove the comment as it was valid only for the 
non-CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX case.

If for some reason you have to send a new version, it would be good to 
mention it is a revert of commit adcf59187e27 ("powerpc: don't use 
direct assignation during early boot.") as it is not necessary anymore 
with CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX

Christophe

> V2: https://lore.kernel.org/all/20260911180536.3234640-2-mkchauras@gmail.com
> 
> V1 -> V2:
> - Comments reworded
> - Commit message reworded
> V1: https://lore.kernel.org/all/20260908064948.999530-1-mkchauras@gmail.com
> 
>   arch/powerpc/Kconfig              | 10 +++++++---
>   arch/powerpc/include/asm/kasan.h  | 11 -----------
>   arch/powerpc/include/asm/string.h | 21 +--------------------
>   arch/powerpc/kernel/cputable.c    | 14 ++------------
>   arch/powerpc/kernel/prom_init.c   | 10 ++--------
>   5 files changed, 12 insertions(+), 54 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 2580e27e4328..b27ed9739eea 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -7,6 +7,10 @@ config CC_HAS_ELFV2
>   config CC_HAS_PREFIXED
>   	def_bool PPC64 && $(cc-option, -mcpu=power10 -mprefixed)
>   
> +config PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> +	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=kernel-address -mllvm -asan-kernel-mem-intrinsic-prefix=1)) || \
> +		 (CC_IS_GCC && $(cc-option,-fsanitize=kernel-address --param asan-kernel-mem-intrinsic-prefix=1))
> +
>   config CC_HAS_PCREL
>   	# Clang has a bug (https://github.com/llvm/llvm-project/issues/62372)
>   	# where pcrel code is not generated if -msoft-float, -mno-altivec, or
> @@ -220,9 +224,9 @@ config PPC
>   	select HAVE_ARCH_HUGE_VMAP		if PPC_RADIX_MMU || PPC_8xx
>   	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			if PPC_BOOK3E_64
> +	select HAVE_ARCH_KASAN			if PPC32 && PAGE_SHIFT <= 14 && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> +	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> +	select HAVE_ARCH_KASAN			if PPC_BOOK3E_64 && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
>   	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
>   	select HAVE_ARCH_KCSAN
>   	select HAVE_ARCH_KFENCE			if ARCH_SUPPORTS_DEBUG_PAGEALLOC
> diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
> index a690e7da53c2..d62756b87ba4 100644
> --- a/arch/powerpc/include/asm/kasan.h
> +++ b/arch/powerpc/include/asm/kasan.h
> @@ -2,20 +2,9 @@
>   #ifndef __ASM_KASAN_H
>   #define __ASM_KASAN_H
>   
> -#if defined(CONFIG_KASAN) && !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX)
> -#define _GLOBAL_KASAN(fn)			\
> -	_GLOBAL(fn);				\
> -	_GLOBAL(__##fn)
> -#define _GLOBAL_TOC_KASAN(fn)			\
> -	_GLOBAL_TOC(fn);			\
> -	_GLOBAL_TOC(__##fn)
> -#define EXPORT_SYMBOL_KASAN(fn)			\
> -	EXPORT_SYMBOL(__##fn)
> -#else /* CONFIG_KASAN && !CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
>   #define _GLOBAL_KASAN(fn)	_GLOBAL(fn)
>   #define _GLOBAL_TOC_KASAN(fn)	_GLOBAL_TOC(fn)
>   #define EXPORT_SYMBOL_KASAN(fn)
> -#endif /* CONFIG_KASAN && !CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
>   
>   #ifndef __ASSEMBLER__
>   
> diff --git a/arch/powerpc/include/asm/string.h b/arch/powerpc/include/asm/string.h
> index 1981bd4036b5..72b5c93a2b84 100644
> --- a/arch/powerpc/include/asm/string.h
> +++ b/arch/powerpc/include/asm/string.h
> @@ -29,29 +29,10 @@ extern void * memchr(const void *,int,__kernel_size_t);
>   void memcpy_flushcache(void *dest, const void *src, size_t size);
>   
>   #ifdef CONFIG_KASAN
> -/* __mem variants are used by KASAN to implement instrumented meminstrinsics. */
> -#ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> +/* Used by mm/kasan/shadow.c as raw backends to bypass KASAN checking. */
>   #define __memset memset
>   #define __memcpy memcpy
>   #define __memmove memmove
> -#else /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
> -void *__memset(void *s, int c, __kernel_size_t count);
> -void *__memcpy(void *to, const void *from, __kernel_size_t n);
> -void *__memmove(void *to, const void *from, __kernel_size_t n);
> -#ifndef __SANITIZE_ADDRESS__
> -/*
> - * For files that are not instrumented (e.g. mm/slub.c) we
> - * should use not instrumented version of mem* functions.
> - */
> -#define memcpy(dst, src, len) __memcpy(dst, src, len)
> -#define memmove(dst, src, len) __memmove(dst, src, len)
> -#define memset(s, c, n) __memset(s, c, n)
> -
> -#ifndef __NO_FORTIFY
> -#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
> -#endif
> -#endif /* !__SANITIZE_ADDRESS__ */
> -#endif /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
>   #endif /* CONFIG_KASAN */
>   
>   #ifdef CONFIG_PPC64
> diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
> index 6f6801da9dc1..6356b5c6be7b 100644
> --- a/arch/powerpc/kernel/cputable.c
> +++ b/arch/powerpc/kernel/cputable.c
> @@ -35,12 +35,7 @@ void __init set_cur_cpu_spec(struct cpu_spec *s)
>   	struct cpu_spec *t = &the_cpu_spec;
>   
>   	t = PTRRELOC(t);
> -	/*
> -	 * use memcpy() instead of *t = *s so that GCC replaces it
> -	 * by __memcpy() when KASAN is active
> -	 */
> -	memcpy(t, s, sizeof(*t));
> -
> +	*t = *s;
>   	*PTRRELOC(&cur_cpu_spec) = &the_cpu_spec;
>   }
>   
> @@ -52,12 +47,7 @@ static struct cpu_spec * __init setup_cpu_spec(unsigned long offset,
>   
>   	t = PTRRELOC(t);
>   	old = *t;
> -
> -	/*
> -	 * Copy everything, then do fixups. Use memcpy() instead of *t = *s
> -	 * so that GCC replaces it by __memcpy() when KASAN is active
> -	 */
> -	memcpy(t, s, sizeof(*t));
> +	*t = *s;
>   
>   	/*
>   	 * If we are overriding a previous value derived from the real
> diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
> index eb9f556b0937..e8e071024da5 100644
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -1362,14 +1362,8 @@ static void __init prom_check_platform_support(void)
>   	int prop_len = prom_getproplen(prom.chosen,
>   				       "ibm,arch-vec-5-platform-support");
>   
> -	/*
> -	 * First copy the architecture vec template
> -	 *
> -	 * use memcpy() instead of *vec = *vec_template so that GCC replaces it
> -	 * by __memcpy() when KASAN is active
> -	 */
> -	memcpy(&ibm_architecture_vec, &ibm_architecture_vec_template,
> -	       sizeof(ibm_architecture_vec));
> +	/* First copy the architecture vec template */
> +	ibm_architecture_vec = ibm_architecture_vec_template;
>   
>   	prom_strscpy_pad(ibm_architecture_vec.vec7.os_id, linux_banner, 256);
>   

Re: [PATCH V3] powerpc/kasan: require memintrinsic prefix support for KASAN

[Mukesh Kumar Chaurasiya]

On Wed, Sep 16, 2026 at 01:09:41PM +0200, Christophe Leroy (CS GROUP) wrote:
> 
> 
> Le 15/09/2026 à 12:09, Mukesh Kumar Chaurasiya (IBM) a écrit :
> > powerpc unconditionally selects GENERIC_ENTRY. The GENERIC_ENTRY
> > infrastructure relies on the compiler emitting __asan_mem*() calls at
> > instrumented mem*() sites rather than plain memset/memcpy/memmove, so
> > that entry/exit paths calling those functions are not instrumented.
> > 
> > This assumption is encoded in two places:
> > 
> >    mm/kasan/shadow.c:
> >      #if !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX) &&
> >          !defined(CONFIG_GENERIC_ENTRY)
> > 
> >    include/linux/fortify-string.h:
> >      #if !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX) &&
> >          !defined(CONFIG_GENERIC_ENTRY)
> > 
> > When GENERIC_ENTRY is set, both guards suppress the C wrappers for
> > memset/memcpy/memmove and the __underlying_mem*() redirections. This
> > is only safe when the compiler supports the prefixed __asan_mem*()
> > intrinsics. On older toolchains (e.g. GCC 9) that lack this support,
> > plain mem*() calls from instrumented code fall through to the raw
> > assembly implementations in mem_64.S / copy_32.S, completely bypassing
> > the KASAN shadow check.
> > 
> > Other arches with GENERIC_ENTRY (x86, s390, loongarch, riscv) do not
> > hit this because their CI toolchains are always new enough to support
> > the prefix flag.
> > 
> > Background: the !GENERIC_ENTRY guard was introduced by commit 69d4c0d32186
> > ("entry, kasan, x86: Disallow overriding mem*() functions", Peter Zijlstra,
> > Jan 2023). The root problem is that the KASAN C wrappers override the
> > linker symbol memset/memcpy/memmove globally, so any call from noinstr or
> > __no_sanitize_address code (e.g. irqentry_enter/irqentry_exit) would still
> > reach the KASAN shadow-check wrapper -- at a point where KASAN invariants
> > may not hold. The compiler prefix approach (Marco Elver, Feb 2023,
> > commit 51287dcb00cc) solves this by having the compiler emit __asan_memset
> > at instrumented call sites and bare memset inside __no_sanitize_address
> > functions, splitting the decision at code-generation time rather than at
> > link time.
> > 
> > A manual C-level override cannot replicate this split: a single linker
> > symbol cannot be made to resolve differently depending on the caller.
> > 
> > x86 also placed its raw memset/memcpy/memmove implementations in
> > .noinstr.text (same commit, 69d4c0d32186), which is the other half of
> > the fix: noinstr callers hit the raw assembly directly, safely bypassing
> > KASAN. PowerPC has not done this. Placing mem_64.S / memcpy_64.S /
> > copy_32.S implementations in .noinstr.text would be the complementary
> > long-term fix that could re-enable KASAN on older toolchains, but it
> > requires care around linker stub overflow on large PPC64 kernels (the
> > same reason powerpc uses NOKPROBE_SYMBOL rather than noinstr for its
> > interrupt handlers -- see the comment in asm/interrupt.h). That work
> > is left as a follow-up.
> > 
> > For now, introduce PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX, an arch-local
> > compiler probe that mirrors the same check as CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> > in lib/Kconfig.kasan but lives outside the 'if KASAN' block to avoid a
> > recursive dependency (CC_HAS_KASAN_MEMINTRINSIC_PREFIX depends on KASAN
> > which depends on HAVE_ARCH_KASAN). Gate the three HAVE_ARCH_KASAN selects
> > on this new symbol so that KASAN is not offered as a config option on
> > toolchains that cannot support it correctly with GENERIC_ENTRY.
> > 
> > Since KASAN on powerpc now unconditionally implies
> > CC_HAS_KASAN_MEMINTRINSIC_PREFIX, the old !CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> > code paths in asm/kasan.h and asm/string.h are dead. Clean them up:
> > 
> > - asm/kasan.h: remove the dual-entry-point variant of _GLOBAL_KASAN /
> >    _GLOBAL_TOC_KASAN / EXPORT_SYMBOL_KASAN that emitted both memset and
> >    __memset as entry points to the same assembly. These aliases were only
> >    needed so the C KASAN wrappers in shadow.c could call __memset() to
> >    reach raw memory ops; with the compiler prefix approach those wrappers
> >    are not used for mem* on powerpc.
> > 
> > - asm/string.h: remove the separate __memset/__memcpy/__memmove symbol
> >    declarations and the memset/memcpy/memmove macro redirections for
> >    uninstrumented files that were needed on old toolchains. Simplify the
> >    CONFIG_KASAN block to just the three #define aliases (still used by
> >    shadow.c as raw backends to bypass KASAN checking).
> > 
> > - cputable.c, prom_init.c: the memcpy is not required now as the manual
> >    instrumentation of memcpy is removed. Hence directly use *dest = *src
> >    for this.
> > 
> > Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
> > Closes: https://lore.kernel.org/all/96dae110-f79b-4e54-8a9b-514369019b5d@linux.ibm.com
> > Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
> > Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
> 
> Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
> 
> > ---
> > Changelog:
> > V2 -> V3:
> > - *dest = *src used instead of memcpy in cputable.c and prom_init.c
> 
> We could have left the memcpy() there but I'm fine either way. What was
> important was to remove the comment as it was valid only for the
> non-CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX case.
>
I thought this would make the code look simpler.
> If for some reason you have to send a new version, it would be good to
> mention it is a revert of commit adcf59187e27 ("powerpc: don't use direct
> assignation during early boot.") as it is not necessary anymore with
> CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> 
I can send out a new version, it's just a commit message change.
> Christophe
> 
Thanks for all the effort in review and explanation.

Regards,
Mukesh

> > V2: https://lore.kernel.org/all/20260911180536.3234640-2-mkchauras@gmail.com
> > 
> > V1 -> V2:
> > - Comments reworded
> > - Commit message reworded
> > V1: https://lore.kernel.org/all/20260908064948.999530-1-mkchauras@gmail.com
> > 
> >   arch/powerpc/Kconfig              | 10 +++++++---
> >   arch/powerpc/include/asm/kasan.h  | 11 -----------
> >   arch/powerpc/include/asm/string.h | 21 +--------------------
> >   arch/powerpc/kernel/cputable.c    | 14 ++------------
> >   arch/powerpc/kernel/prom_init.c   | 10 ++--------
> >   5 files changed, 12 insertions(+), 54 deletions(-)
> > 
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 2580e27e4328..b27ed9739eea 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -7,6 +7,10 @@ config CC_HAS_ELFV2
> >   config CC_HAS_PREFIXED
> >   	def_bool PPC64 && $(cc-option, -mcpu=power10 -mprefixed)
> > +config PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> > +	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=kernel-address -mllvm -asan-kernel-mem-intrinsic-prefix=1)) || \
> > +		 (CC_IS_GCC && $(cc-option,-fsanitize=kernel-address --param asan-kernel-mem-intrinsic-prefix=1))
> > +
> >   config CC_HAS_PCREL
> >   	# Clang has a bug (https://github.com/llvm/llvm-project/issues/62372)
> >   	# where pcrel code is not generated if -msoft-float, -mno-altivec, or
> > @@ -220,9 +224,9 @@ config PPC
> >   	select HAVE_ARCH_HUGE_VMAP		if PPC_RADIX_MMU || PPC_8xx
> >   	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			if PPC_BOOK3E_64
> > +	select HAVE_ARCH_KASAN			if PPC32 && PAGE_SHIFT <= 14 && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> > +	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> > +	select HAVE_ARCH_KASAN			if PPC_BOOK3E_64 && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> >   	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
> >   	select HAVE_ARCH_KCSAN
> >   	select HAVE_ARCH_KFENCE			if ARCH_SUPPORTS_DEBUG_PAGEALLOC
> > diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
> > index a690e7da53c2..d62756b87ba4 100644
> > --- a/arch/powerpc/include/asm/kasan.h
> > +++ b/arch/powerpc/include/asm/kasan.h
> > @@ -2,20 +2,9 @@
> >   #ifndef __ASM_KASAN_H
> >   #define __ASM_KASAN_H
> > -#if defined(CONFIG_KASAN) && !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX)
> > -#define _GLOBAL_KASAN(fn)			\
> > -	_GLOBAL(fn);				\
> > -	_GLOBAL(__##fn)
> > -#define _GLOBAL_TOC_KASAN(fn)			\
> > -	_GLOBAL_TOC(fn);			\
> > -	_GLOBAL_TOC(__##fn)
> > -#define EXPORT_SYMBOL_KASAN(fn)			\
> > -	EXPORT_SYMBOL(__##fn)
> > -#else /* CONFIG_KASAN && !CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
> >   #define _GLOBAL_KASAN(fn)	_GLOBAL(fn)
> >   #define _GLOBAL_TOC_KASAN(fn)	_GLOBAL_TOC(fn)
> >   #define EXPORT_SYMBOL_KASAN(fn)
> > -#endif /* CONFIG_KASAN && !CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
> >   #ifndef __ASSEMBLER__
> > diff --git a/arch/powerpc/include/asm/string.h b/arch/powerpc/include/asm/string.h
> > index 1981bd4036b5..72b5c93a2b84 100644
> > --- a/arch/powerpc/include/asm/string.h
> > +++ b/arch/powerpc/include/asm/string.h
> > @@ -29,29 +29,10 @@ extern void * memchr(const void *,int,__kernel_size_t);
> >   void memcpy_flushcache(void *dest, const void *src, size_t size);
> >   #ifdef CONFIG_KASAN
> > -/* __mem variants are used by KASAN to implement instrumented meminstrinsics. */
> > -#ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> > +/* Used by mm/kasan/shadow.c as raw backends to bypass KASAN checking. */
> >   #define __memset memset
> >   #define __memcpy memcpy
> >   #define __memmove memmove
> > -#else /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
> > -void *__memset(void *s, int c, __kernel_size_t count);
> > -void *__memcpy(void *to, const void *from, __kernel_size_t n);
> > -void *__memmove(void *to, const void *from, __kernel_size_t n);
> > -#ifndef __SANITIZE_ADDRESS__
> > -/*
> > - * For files that are not instrumented (e.g. mm/slub.c) we
> > - * should use not instrumented version of mem* functions.
> > - */
> > -#define memcpy(dst, src, len) __memcpy(dst, src, len)
> > -#define memmove(dst, src, len) __memmove(dst, src, len)
> > -#define memset(s, c, n) __memset(s, c, n)
> > -
> > -#ifndef __NO_FORTIFY
> > -#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
> > -#endif
> > -#endif /* !__SANITIZE_ADDRESS__ */
> > -#endif /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
> >   #endif /* CONFIG_KASAN */
> >   #ifdef CONFIG_PPC64
> > diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
> > index 6f6801da9dc1..6356b5c6be7b 100644
> > --- a/arch/powerpc/kernel/cputable.c
> > +++ b/arch/powerpc/kernel/cputable.c
> > @@ -35,12 +35,7 @@ void __init set_cur_cpu_spec(struct cpu_spec *s)
> >   	struct cpu_spec *t = &the_cpu_spec;
> >   	t = PTRRELOC(t);
> > -	/*
> > -	 * use memcpy() instead of *t = *s so that GCC replaces it
> > -	 * by __memcpy() when KASAN is active
> > -	 */
> > -	memcpy(t, s, sizeof(*t));
> > -
> > +	*t = *s;
> >   	*PTRRELOC(&cur_cpu_spec) = &the_cpu_spec;
> >   }
> > @@ -52,12 +47,7 @@ static struct cpu_spec * __init setup_cpu_spec(unsigned long offset,
> >   	t = PTRRELOC(t);
> >   	old = *t;
> > -
> > -	/*
> > -	 * Copy everything, then do fixups. Use memcpy() instead of *t = *s
> > -	 * so that GCC replaces it by __memcpy() when KASAN is active
> > -	 */
> > -	memcpy(t, s, sizeof(*t));
> > +	*t = *s;
> >   	/*
> >   	 * If we are overriding a previous value derived from the real
> > diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
> > index eb9f556b0937..e8e071024da5 100644
> > --- a/arch/powerpc/kernel/prom_init.c
> > +++ b/arch/powerpc/kernel/prom_init.c
> > @@ -1362,14 +1362,8 @@ static void __init prom_check_platform_support(void)
> >   	int prop_len = prom_getproplen(prom.chosen,
> >   				       "ibm,arch-vec-5-platform-support");
> > -	/*
> > -	 * First copy the architecture vec template
> > -	 *
> > -	 * use memcpy() instead of *vec = *vec_template so that GCC replaces it
> > -	 * by __memcpy() when KASAN is active
> > -	 */
> > -	memcpy(&ibm_architecture_vec, &ibm_architecture_vec_template,
> > -	       sizeof(ibm_architecture_vec));
> > +	/* First copy the architecture vec template */
> > +	ibm_architecture_vec = ibm_architecture_vec_template;
> >   	prom_strscpy_pad(ibm_architecture_vec.vec7.os_id, linux_banner, 256);
> 

Re: [PATCH V3] powerpc/kasan: require memintrinsic prefix support for KASAN

[Andrey Ryabinin]

"Mukesh Kumar Chaurasiya (IBM)" <mkchauras@gmail.com> writes:

Hi,
I fed this patch to an AI for review, and the review results are included below.
Please take a look. From my side, I agree with all of the points
raised by AI in the
review, and I think they all need to be addressed. There is also a diff with
the suggested changes at the very end of this mail.


> powerpc unconditionally selects GENERIC_ENTRY. The GENERIC_ENTRY
> infrastructure relies on the compiler emitting __asan_mem*() calls at
> instrumented mem*() sites rather than plain memset/memcpy/memmove, so
> that entry/exit paths calling those functions are not instrumented.
>
> [ ... ]
>
> When GENERIC_ENTRY is set, both guards suppress the C wrappers for
> memset/memcpy/memmove and the __underlying_mem*() redirections. This
> is only safe when the compiler supports the prefixed __asan_mem*()
> intrinsics. On older toolchains (e.g. GCC 9) that lack this support,
> plain mem*() calls from instrumented code fall through to the raw
> assembly implementations in mem_64.S / copy_32.S, completely bypassing
> the KASAN shadow check.
>
> Other arches with GENERIC_ENTRY (x86, s390, loongarch, riscv) do not
> hit this because their CI toolchains are always new enough to support
> the prefix flag.
>
> [ ... ]
>
> Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
> Closes: https://lore.kernel.org/all/96dae110-f79b-4e54-8a9b-514369019b5d@linux.ibm.com
> Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>

The thread in the Closes: link is about an early boot hang, but the
commit message only describes mem*() calls bypassing the shadow check.
Bypassed checks would lose coverage, not hang the machine.  Is the
mechanism of the hang understood?

Looking at the state before this commit, the !CC_HAS_KASAN_MEMINTRINSIC_PREFIX
macros that bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") added to
asm/kasan.h emit two ELFv2 global entry points back to back:

  #define _GLOBAL_TOC_KASAN(fn)
          _GLOBAL_TOC(fn);
          _GLOBAL_TOC(__##fn)

With the _GLOBAL_TOC() definition from asm/ppc_asm.h that expands, for
memcpy_64.S, to:

  memcpy:
  0:      addis r2,r12,(.TOC.-0b)@ha
          addi  r2,r2,(.TOC.-0b)@l
          .localentry memcpy,.-memcpy       <- local entry is memcpy+8
  __memcpy:
  0:      addis r2,r12,(.TOC.-0b)@ha        <- this is memcpy+8
          addi  r2,r2,(.TOC.-0b)@l
          .localentry __memcpy,.-__memcpy

Assembling exactly that for powerpc64le gives memcpy st_other 0x60
(local entry offset 8), and memcpy+8 is the __memcpy TOC prologue.

Every same-TOC caller of memcpy() or memmove() is resolved by the
linker to the local entry, so it lands on that second prologue with r12
holding whatever the caller left there, and returns with r2 pointing
at garbage.  Same-TOC callers do not reload r2 after the call.  With
GENERIC_ENTRY, mm/kasan/shadow.c no longer provides memcpy(), so on a
toolchain without the prefix parameter every instrumented file calls
the memcpy symbol directly and hits this.  That matches an early hang
that only shows up with GCC 9.

This commit makes the hang go away because the dual-entry macro is
deleted, but the commit message attributes the fix to something else.
Could the message describe the r2 corruption, and since this repairs a
regression from the GENERIC_ENTRY conversion, should it carry:

  Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")

On the claim that other GENERIC_ENTRY architectures "do not hit this
because their CI toolchains are always new enough": x86, s390, riscv
and loongarch with GCC 8 to 12 build exactly the same configuration,
CONFIG_KASAN=y without CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX, and
run with mem*() unchecked.  scripts/Makefile.kasan documents that as
the intended behaviour:

  # Instrument memcpy/memset/memmove calls by using instrumented __asan_mem*()
  # instead. With compilers that don't support this option, compiler-inserted
  # memintrinsics won't be checked by KASAN on GENERIC_ENTRY architectures.

and mm/kasan/kasan_test_c.c skips the affected tests with "Test
requires checked mem*()".  So the situation the message describes is
the accepted upstream state for old toolchains, not something specific
to powerpc.

> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 2580e27e4328..b27ed9739eea 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -7,6 +7,10 @@ config CC_HAS_ELFV2
>  config CC_HAS_PREFIXED
>  	def_bool PPC64 && $(cc-option, -mcpu=power10 -mprefixed)
>
> +config PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> +	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=kernel-address -mllvm -asan-kernel-mem-intrinsic-prefix=1)) || \
> +		 (CC_IS_GCC && $(cc-option,-fsanitize=kernel-address --param asan-kernel-mem-intrinsic-prefix=1))
> +
>  config CC_HAS_PCREL
>  	# Clang has a bug (https://github.com/llvm/llvm-project/issues/62372)
>  	# where pcrel code is not generated if -msoft-float, -mno-altivec, or

[ ... ]

> @@ -220,9 +224,9 @@ config PPC
>  	select HAVE_ARCH_HUGE_VMAP		if PPC_RADIX_MMU || PPC_8xx
>  	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			if PPC_BOOK3E_64
> +	select HAVE_ARCH_KASAN			if PPC32 && PAGE_SHIFT <= 14 && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> +	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> +	select HAVE_ARCH_KASAN			if PPC_BOOK3E_64 && PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
>  	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
>  	select HAVE_ARCH_KCSAN
>  	select HAVE_ARCH_KFENCE			if ARCH_SUPPORTS_DEBUG_PAGEALLOC

This drops KASAN from powerpc entirely for GCC 8 through 12, which are
inside the supported range in Documentation/process/changes.rst (GNU C
8.1 minimum).  An existing .config with CONFIG_KASAN=y silently loses
it on olddefconfig once HAVE_ARCH_KASAN is no longer selected.

Given that the actual breakage is the broken memcpy/memmove entry
points, is it necessary to go this far?  Keeping one _GLOBAL_TOC()
prologue for __memcpy and making memcpy a plain alias of it (a second
label plus a matching .localentry, or a global entry that branches to
__memcpy) would restore the pre-GENERIC_ENTRY behaviour, with mem*()
unchecked on old compilers exactly like the other GENERIC_ENTRY
architectures.  That also keeps a Fixes-tagged backport candidate from
removing a feature on stable kernels.


> diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
> index a690e7da53c2..d62756b87ba4 100644
> --- a/arch/powerpc/include/asm/kasan.h
> +++ b/arch/powerpc/include/asm/kasan.h
> @@ -2,20 +2,9 @@
>  #ifndef __ASM_KASAN_H
>  #define __ASM_KASAN_H
>
> -#if defined(CONFIG_KASAN) && !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX)
> -#define _GLOBAL_KASAN(fn)			\
> -	_GLOBAL(fn);				\
> -	_GLOBAL(__##fn)
> -#define _GLOBAL_TOC_KASAN(fn)			\
> -	_GLOBAL_TOC(fn);			\
> -	_GLOBAL_TOC(__##fn)
> -#define EXPORT_SYMBOL_KASAN(fn)			\
> -	EXPORT_SYMBOL(__##fn)
> -#else /* CONFIG_KASAN && !CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
>  #define _GLOBAL_KASAN(fn)	_GLOBAL(fn)
>  #define _GLOBAL_TOC_KASAN(fn)	_GLOBAL_TOC(fn)
>  #define EXPORT_SYMBOL_KASAN(fn)
> -#endif /* CONFIG_KASAN && !CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
>
>  #ifndef __ASSEMBLER__
>

this isn't a bug, but after this change _GLOBAL_KASAN(), _GLOBAL_TOC_KASAN()
and EXPORT_SYMBOL_KASAN() are unconditional identity macros with a single
empty one.  Should the five users in mem_64.S, memcpy_64.S and copy_32.S
switch to _GLOBAL()/_GLOBAL_TOC() and the macros go away?

Related leftover: arch/powerpc/kernel/prom_init_check.sh still has

  has_renamed_memintrinsics()
  {
          grep -q "^CONFIG_KASAN=y$" "${KCONFIG_CONFIG}" && \
                  ! grep -q
"^CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX=y" "${KCONFIG_CONFIG}"
  }

  if has_renamed_memintrinsics
  then
          MEM_FUNCS="__memcpy __memset"

which can no longer be true on powerpc after this commit.  Should that
branch be removed in the same cleanup?

> diff --git a/arch/powerpc/include/asm/string.h b/arch/powerpc/include/asm/string.h
> index 1981bd4036b5..72b5c93a2b84 100644
> --- a/arch/powerpc/include/asm/string.h
> +++ b/arch/powerpc/include/asm/string.h
> @@ -29,29 +29,10 @@ extern void * memchr(const void *,int,__kernel_size_t);
>  void memcpy_flushcache(void *dest, const void *src, size_t size);
>
>  #ifdef CONFIG_KASAN
> -/* __mem variants are used by KASAN to implement instrumented meminstrinsics. */
> -#ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> +/* Used by mm/kasan/shadow.c as raw backends to bypass KASAN checking. */
>  #define __memset memset

this isn't a bug, but the new comment names only mm/kasan/shadow.c.
The same __memset()/__memcpy() names are used by mm/kasan/generic.c as
well (DEFINE_ASAN_SET_SHADOW() and release_alloc_meta()), so would
"used by mm/kasan as raw backends" be more accurate?


---
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index b27ed9739eea..2580e27e4328 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -7,10 +7,6 @@ config CC_HAS_ELFV2
 config CC_HAS_PREFIXED
 	def_bool PPC64 && $(cc-option, -mcpu=power10 -mprefixed)

-config PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
-	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=kernel-address
-mllvm -asan-kernel-mem-intrinsic-prefix=1)) || \
-		 (CC_IS_GCC && $(cc-option,-fsanitize=kernel-address --param
asan-kernel-mem-intrinsic-prefix=1))
-
 config CC_HAS_PCREL
 	# Clang has a bug (https://github.com/llvm/llvm-project/issues/62372)
 	# where pcrel code is not generated if -msoft-float, -mno-altivec, or
@@ -224,9 +220,9 @@ config PPC
 	select HAVE_ARCH_HUGE_VMAP		if PPC_RADIX_MMU || PPC_8xx
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
-	select HAVE_ARCH_KASAN			if PPC32 && PAGE_SHIFT <= 14 &&
PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
-	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU &&
PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
-	select HAVE_ARCH_KASAN			if PPC_BOOK3E_64 &&
PPC_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+	select HAVE_ARCH_KASAN			if PPC32 && PAGE_SHIFT <= 14
+	select HAVE_ARCH_KASAN			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
 	select HAVE_ARCH_KFENCE			if ARCH_SUPPORTS_DEBUG_PAGEALLOC
diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
index d62756b87ba4..599a9e02af02 100644
--- a/arch/powerpc/include/asm/kasan.h
+++ b/arch/powerpc/include/asm/kasan.h
@@ -2,10 +2,6 @@
 #ifndef __ASM_KASAN_H
 #define __ASM_KASAN_H

-#define _GLOBAL_KASAN(fn)	_GLOBAL(fn)
-#define _GLOBAL_TOC_KASAN(fn)	_GLOBAL_TOC(fn)
-#define EXPORT_SYMBOL_KASAN(fn)
-
 #ifndef __ASSEMBLER__

 #include <asm/page.h>
diff --git a/arch/powerpc/kernel/prom_init_check.sh
b/arch/powerpc/kernel/prom_init_check.sh
index 3090b97258ae..3155cc722e48 100644
--- a/arch/powerpc/kernel/prom_init_check.sh
+++ b/arch/powerpc/kernel/prom_init_check.sh
@@ -13,21 +13,8 @@
 # If you really need to reference something from prom_init.o add
 # it to the list below:

-has_renamed_memintrinsics()
-{
-	grep -q "^CONFIG_KASAN=y$" "${KCONFIG_CONFIG}" && \
-		! grep -q "^CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX=y" "${KCONFIG_CONFIG}"
-}
-
-if has_renamed_memintrinsics
-then
-	MEM_FUNCS="__memcpy __memset"
-else
-	MEM_FUNCS="memcpy memset"
-fi
-
 WHITELIST="add_reloc_offset __bss_start __bss_stop copy_and_flush
-_end enter_prom $MEM_FUNCS reloc_offset __secondary_hold
+_end enter_prom memcpy memset reloc_offset __secondary_hold
 __secondary_hold_acknowledge __secondary_hold_spinloop __start
 logo_linux_clut224 btext_prepare_BAT
 reloc_got2 kernstart_addr memstart_addr linux_banner _stext
diff --git a/arch/powerpc/lib/copy_32.S b/arch/powerpc/lib/copy_32.S
index 933b685e7ab6..97eb9ca0cc23 100644
--- a/arch/powerpc/lib/copy_32.S
+++ b/arch/powerpc/lib/copy_32.S
@@ -10,7 +10,6 @@
 #include <asm/errno.h>
 #include <asm/ppc_asm.h>
 #include <asm/code-patching-asm.h>
-#include <asm/kasan.h>

 #define COPY_16_BYTES		\
 	lwz	r7,4(r4);	\
@@ -87,7 +86,7 @@ EXPORT_SYMBOL(memset16)
  * We therefore skip the optimised bloc that uses dcbz. This jump is
  * replaced by a nop once cache is active. This is done in machine_init()
  */
-_GLOBAL_KASAN(memset)
+_GLOBAL(memset)
 	cmplwi	0,r5,4
 	blt	7f

@@ -147,7 +146,6 @@ _GLOBAL_KASAN(memset)
 	bdnz	9b
 	blr
 EXPORT_SYMBOL(memset)
-EXPORT_SYMBOL_KASAN(memset)

 /*
  * This version uses dcbz on the complete cache lines in the
@@ -160,12 +158,12 @@ EXPORT_SYMBOL_KASAN(memset)
  * We therefore jump to generic_memcpy which doesn't use dcbz. This jump is
  * replaced by a nop once cache is active. This is done in machine_init()
  */
-_GLOBAL_KASAN(memmove)
+_GLOBAL(memmove)
 	cmplw	0,r3,r4
 	bgt	backwards_memcpy
 	/* fall through */

-_GLOBAL_KASAN(memcpy)
+_GLOBAL(memcpy)
 1:	b	generic_memcpy
 	patch_site	1b, patch__memcpy_nocache

@@ -241,8 +239,6 @@ _GLOBAL_KASAN(memcpy)
 65:	blr
 EXPORT_SYMBOL(memcpy)
 EXPORT_SYMBOL(memmove)
-EXPORT_SYMBOL_KASAN(memcpy)
-EXPORT_SYMBOL_KASAN(memmove)

 generic_memcpy:
 	srwi.	r7,r5,3
diff --git a/arch/powerpc/lib/mem_64.S b/arch/powerpc/lib/mem_64.S
index 6fd06cd20faa..40eaedd31486 100644
--- a/arch/powerpc/lib/mem_64.S
+++ b/arch/powerpc/lib/mem_64.S
@@ -8,7 +8,6 @@
 #include <asm/processor.h>
 #include <asm/errno.h>
 #include <asm/ppc_asm.h>
-#include <asm/kasan.h>

 #ifndef CONFIG_KASAN
 _GLOBAL(__memset16)
@@ -29,7 +28,7 @@ EXPORT_SYMBOL(__memset32)
 EXPORT_SYMBOL(__memset64)
 #endif

-_GLOBAL_KASAN(memset)
+_GLOBAL(memset)
 	neg	r0,r3
 	rlwimi	r4,r4,8,16,23
 	andi.	r0,r0,7			/* # bytes to be 8-byte aligned */
@@ -95,9 +94,8 @@ _GLOBAL_KASAN(memset)
 	stb	r4,0(r6)
 	blr
 EXPORT_SYMBOL(memset)
-EXPORT_SYMBOL_KASAN(memset)

-_GLOBAL_TOC_KASAN(memmove)
+_GLOBAL_TOC(memmove)
 	cmplw	0,r3,r4
 	bgt	backwards_memcpy
 	b	memcpy
@@ -139,4 +137,3 @@ _GLOBAL(backwards_memcpy)
 	mtctr	r7
 	b	1b
 EXPORT_SYMBOL(memmove)
-EXPORT_SYMBOL_KASAN(memmove)
diff --git a/arch/powerpc/lib/memcpy_64.S b/arch/powerpc/lib/memcpy_64.S
index b5a67e20143f..0cedd455231a 100644
--- a/arch/powerpc/lib/memcpy_64.S
+++ b/arch/powerpc/lib/memcpy_64.S
@@ -7,7 +7,6 @@
 #include <asm/ppc_asm.h>
 #include <asm/asm-compat.h>
 #include <asm/feature-fixups.h>
-#include <asm/kasan.h>

 #ifndef SELFTEST_CASE
 /* For big-endian, 0 == most CPUs, 1 == POWER6, 2 == Cell */
@@ -15,7 +14,7 @@
 #endif

 	.align	7
-_GLOBAL_TOC_KASAN(memcpy)
+_GLOBAL_TOC(memcpy)
 BEGIN_FTR_SECTION
 #ifdef __LITTLE_ENDIAN__
 	cmpdi	cr7,r5,0
@@ -227,4 +226,3 @@ END_FTR_SECTION_IFCLR(CPU_FTR_UNALIGNED_LD_STD)
 	blr
 #endif
 EXPORT_SYMBOL(memcpy)
-EXPORT_SYMBOL_KASAN(memcpy)