Re: [PATCH V2] powerpc/text-patching: simplify the implementation of ppc_kallsyms_lookup_name()

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 06/05/2026 à 04:11, Xie Yuanbin a écrit :
> 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>
> Suggested-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
> Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>

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

> ---
> v1->v2: https://lore.kernel.org/20260205100517.292858-2-xieyuanbin1@huawei.com
>    - Not use strlen()
> 
>   arch/powerpc/include/asm/text-patching.h | 50 ++++++++----------------
>   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