[PATCH V4] powerpc/kasan: fix r2 corruption in mem*() on GENERIC_ENTRY with old compilers

["Mukesh Kumar Chaurasiya (IBM)" <mkchauras@gmail.com>]

bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") introduced
a bug that, when CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX is not
set, expand to two consecutive ELFv2 global entry points for the
same function body:

  _GLOBAL_TOC_KASAN(memcpy) expands to:
    _GLOBAL_TOC(memcpy);
    _GLOBAL_TOC(__memcpy)

On powerpc64le this produces:

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

The assembler sets memcpy's st_other field so its local entry offset is
8 bytes past the global entry point.  The linker resolves same-TOC
calls to the local entry, so every same-TOC caller of memcpy() lands
at memcpy+8 — which is the beginning of the __memcpy global-entry TOC
prologue.  That prologue uses r12 as the base to recompute r2, but r12
holds whatever the caller left in it (not the address of memcpy+8).
The result is r2 pointing at garbage on return.  Same-TOC callers do
not reload r2 after the call, so the first TOC-relative access after
returning from memcpy() or memmove() crashes or silently corrupts data.

With GENERIC_ENTRY selected, mm/kasan/shadow.c no longer provides its
own memcpy()/memmove()/memset() wrappers, so on a toolchain without
-mllvm -asan-kernel-mem-intrinsic-prefix=1 (e.g. GCC 9) every
instrumented file resolves mem*() directly to the assembly symbols and
hits this corrupt-r2 path.  This manifests as an early boot hang unique
to powerpc with GCC 9 and CONFIG_KASAN=y.

Fix this by removing the dual-entry macros entirely.  The assembly
files in mem_64.S, memcpy_64.S and copy_32.S now use plain
_GLOBAL()/_GLOBAL_TOC() for memset/memcpy/memmove, emitting a single
correct ELFv2 entry point.  The __mem* aliases required by mm/kasan
(used in mm/kasan/shadow.c and mm/kasan/generic.c as raw backends to
bypass KASAN checking) are provided entirely through the #define
redirections in asm/string.h, which already handles both the
CC_HAS_KASAN_MEMINTRINSIC_PREFIX and non-prefix cases in C.

As a consequence the _GLOBAL_KASAN(), _GLOBAL_TOC_KASAN() and
EXPORT_SYMBOL_KASAN() macros have no remaining users and are removed
from asm/kasan.h.  The has_renamed_memintrinsics() branch in
prom_init_check.sh, which conditionally whitelisted __memcpy/__memset
when CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX was absent, is dead code
after this change and is removed; the whitelist now unconditionally
lists memcpy and memset.

Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
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:
V3 -> V4:
- Kasan only disabled for mem intrinsics function for older compilers
V3: https://lore.kernel.org/all/20260915100938.1337401-1-mkchauras@gmail.com
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/include/asm/kasan.h       | 15 ---------------
 arch/powerpc/include/asm/string.h      | 21 +--------------------
 arch/powerpc/kernel/cputable.c         | 14 +++-----------
 arch/powerpc/kernel/prom_init.c        | 10 ++--------
 arch/powerpc/kernel/prom_init_check.sh | 15 +--------------
 arch/powerpc/lib/copy_32.S             | 10 +++-------
 arch/powerpc/lib/mem_64.S              |  7 ++-----
 arch/powerpc/lib/memcpy_64.S           |  4 +---
 8 files changed, 13 insertions(+), 83 deletions(-)

diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
index a690e7da53c2..599a9e02af02 100644
--- a/arch/powerpc/include/asm/kasan.h
+++ b/arch/powerpc/include/asm/kasan.h
@@ -2,21 +2,6 @@
 #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__
 
 #include <asm/page.h>
diff --git a/arch/powerpc/include/asm/string.h b/arch/powerpc/include/asm/string.h
index 1981bd4036b5..161b949683b3 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 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..4731e27bb7bc 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;
 }
 
@@ -53,11 +48,8 @@ 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));
+	/* Copy everything, then do fixups. */
+	*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);
 
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)
-- 
2.55.0