Re: [PATCH 2/2] powerpc/text-patching: Fix possible stringop-overread compilation error

[Xie Yuanbin <xieyuanbin1@huawei.com>]

Hi, Christophe Leroy!

On Mon, 9 Feb 2026 14:41:51 +0100, Christophe Leroy (CS GROUP) wrote:
> On 09/02/2026 14:25, Xie Yuanbin wrote:
>> When CONFIG_PPC64_ELF_ABI_V1=y, it seems that the try of lookupinp
>> the original non-dot symbol is missing.
>>
>> What about this (Only the compilation test is performed):
>> ```c
>> static inline unsigned long __ppc_kallsyms_lookup_name(const char *name)
>> {
>> 	unsigned long addr = kallsyms_lookup_name(name);
>>
>> 	if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2) && addr)
>> 		addr = ppc_function_entry((void *)addr);
>>
>> 	return addr;
>> }
>>
>> #define ppc_kallsyms_lookup_name(x) ({					\
>> 		unsigned long addr = 0;					\
>> 		if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V1))		\
>> 			addr = __ppc_kallsyms_lookup_name("." x);	\
>> 		if (!addr)						\
>> 			addr = __ppc_kallsyms_lookup_name(x);		\
>> 		addr;							\
>> 	})
>> ```
>
> Good point.
>
> To avoid duplicating the string I'd suggest:
>
> static inline unsigned long __ppc_kallsyms_lookup_name(const char *name)
> {
> 	unsigned long addr = kallsyms_lookup_name(name);
>
> 	if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V1) && !addr)
> 		addr = kallsyms_lookup_name(name + 1);
> 	if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2) && addr)
> 		addr = ppc_function_entry((void *)addr);
>
> 	return addr;
> }
>
> #ifdef CONFIG_PPC64_ELF_ABI_V1
> #define ppc_kallsyms_lookup_name(x)	__ppc_kallsyms_lookup_name("." x);
> #else
> #define ppc_kallsyms_lookup_name(x)	__ppc_kallsyms_lookup_name(x)
> #endif

I would like to submit the modification as a new patch, and include you
as Co-developer. Do you agree?

Full of the patch:
```patch
From fbf07e5c1a97da7c8572435537f2b92213ede39d Mon Sep 17 00:00:00 2001
From: Xie Yuanbin <xieyuanbin1@huawei.com>
Date: Thu, 30 Apr 2026 14:15:26 +0800
Subject: [PATCH V2] powerpc/text-patching: simplify the implementation of ppc_kallsyms_lookup_name()

ppc_kallsyms_lookup_name() is called only twice in the kernel code, and
the parameters are all constant strings. strnlen(name, KSYM_NAME_LEN) is
called inside ppc_kallsyms_lookup_name(), when the compiler detects that
KSYM_NAME_LEN is larger then the constant strings,
the following error will be triggered:
```log
  CC      arch/powerpc/kernel/optprobes.o
In file included from ./arch/powerpc/include/asm/kprobes.h:24,
                 from ./include/linux/kprobes.h:31,
                 from arch/powerpc/kernel/optprobes.c:8:
In function ‘ppc_kallsyms_lookup_name’,
    inlined from ‘arch_prepare_optimized_kprobe’ at arch/powerpc/kernel/optprobes.c:209:21:
./arch/powerpc/include/asm/text-patching.h:232:13: error: ‘strnlen’ specified bound 512 exceeds source size 19 [-Werror=stringop-overread]
  232 |         if (strnlen(name, KSYM_NAME_LEN) >= KSYM_NAME_LEN)
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘ppc_kallsyms_lookup_name’,
    inlined from ‘arch_prepare_optimized_kprobe’ at arch/powerpc/kernel/optprobes.c:210:22:
./arch/powerpc/include/asm/text-patching.h:232:13: error: ‘strnlen’ specified bound 512 exceeds source size 13 [-Werror=stringop-overread]
  232 |         if (strnlen(name, KSYM_NAME_LEN) >= KSYM_NAME_LEN)
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
```

The error can be reproduced in the following ways:
Use lastest linux-next source, change ppc_kallsyms_lookup_name() to
__always_inline, use default ppc64_defconfig, set CONFIG_EXPERT=y,
CONFIG_PPC64_BIG_ENDIAN_ELF_ABI_V2=n, CONFIG_CC_OPTIMIZE_FOR_SIZE=y,
and use gcc-14 or a later version for compilation.

Since ppc_kallsyms_lookup_name() is called only twice in the kernel,
and the parameters are all constant strins, simplify the implementation
of ppc_kallsyms_lookup_name() and avoid calling strnlen().

Cc: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: Kees Cook <kees@kernel.org>
Co-developed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
---
v1->v2: https://lore.kernel.org/20260205100517.292858-2-xieyuanbin1@huawei.com
  - Not use strlen()

 arch/powerpc/include/asm/text-patching.h | 42 ++++++++----------------
 1 file changed, 17 insertions(+), 33 deletions(-)

diff --git a/arch/powerpc/include/asm/text-patching.h b/arch/powerpc/include/asm/text-patching.h
index e7f14720f630..2d3f698cb4f1 100644
--- a/arch/powerpc/include/asm/text-patching.h
+++ b/arch/powerpc/include/asm/text-patching.h
@@ -221,39 +221,23 @@ static inline unsigned long ppc_global_function_entry(void *func)
  * - For ABIv1, we lookup the dot variant.
  * - For ABIv2, we return the local entry point.
  */
-static inline unsigned long ppc_kallsyms_lookup_name(const char *name)
-{
-	unsigned long addr;
-#ifdef CONFIG_PPC64_ELF_ABI_V1
-	/* check for dot variant */
-	char dot_name[1 + KSYM_NAME_LEN];
-	bool dot_appended = false;
-
-	if (strnlen(name, KSYM_NAME_LEN) >= KSYM_NAME_LEN)
-		return 0;
-
-	if (name[0] != '.') {
-		dot_name[0] = '.';
-		dot_name[1] = '\0';
-		strlcat(dot_name, name, sizeof(dot_name));
-		dot_appended = true;
-	} else {
-		dot_name[0] = '\0';
-		strlcat(dot_name, name, sizeof(dot_name));
-	}
-	addr = kallsyms_lookup_name(dot_name);
-	if (!addr && dot_appended)
-		/* Let's try the original non-dot symbol lookup	*/
-		addr = kallsyms_lookup_name(name);
-#elif defined(CONFIG_PPC64_ELF_ABI_V2)
-	addr = kallsyms_lookup_name(name);
-	if (addr)
-		addr = ppc_function_entry((void *)addr);
-#else
-	addr = kallsyms_lookup_name(name);
-#endif
-	return addr;
-}
+static inline unsigned long __ppc_kallsyms_lookup_name(const char *name)
+{
+	unsigned long addr = kallsyms_lookup_name(name);
+
+	if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V1) && !addr)
+		addr = kallsyms_lookup_name(name + 1);
+	if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2) && addr)
+		addr = ppc_function_entry((void *)addr);
+
+	return addr;
+}
+
+#ifdef CONFIG_PPC64_ELF_ABI_V1
+#define ppc_kallsyms_lookup_name(x)	__ppc_kallsyms_lookup_name("." x)
+#else
+#define ppc_kallsyms_lookup_name(x)	__ppc_kallsyms_lookup_name(x)
+#endif
 
 /*
  * Some instruction encodings commonly used in dynamic ftracing
-- 
2.53.0
```