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

From: Kees Cook <[email-masked]>
Date: Fri, 6 Feb 2026 10:26:47 -0800

On Thu, Feb 05, 2026 at 06:05:17PM +0800, Xie Yuanbin wrote:
> For strnlen(), if the compiler detects that the maxlen argument exceeds
> the valid memory size of the input string object, a compilation error may
> occur.
> 
> For lastest linux-next source, changing ppc_kallsyms_lookup_name() to
> __always_inline, using default ppc64_defconfig, and setting
> CONFIG_EXPERT=y, CONFIG_PPC64_BIG_ENDIAN_ELF_ABI_V2=n,
> CONFIG_CC_OPTIMIZE_FOR_SIZE=y. Then, when using gcc-15 for compilation,
> 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
> ```
> 
> Refer to the implementation of fortify's strnlen(). If the string length
> is a compile-time constant, do not call the strnlen() function.
> 
> Signed-off-by: Xie Yuanbin <[email-masked]>
> ---
>  arch/powerpc/include/asm/text-patching.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/text-patching.h b/arch/powerpc/include/asm/text-patching.h
> index e7f14720f630..ce1b2131980a 100644
> --- a/arch/powerpc/include/asm/text-patching.h
> +++ b/arch/powerpc/include/asm/text-patching.h
> @@ -228,8 +228,13 @@ static inline unsigned long ppc_kallsyms_lookup_name(const char *name)
>  	/* check for dot variant */
>  	char dot_name[1 + KSYM_NAME_LEN];
>  	bool dot_appended = false;
> +	size_t n_len = __compiletime_strlen(name);
> +	const size_t n_size = __member_size(name);
>  
> -	if (strnlen(name, KSYM_NAME_LEN) >= KSYM_NAME_LEN)
> +	if (n_len == SIZE_MAX || KSYM_NAME_LEN < n_size)
> +		n_len = strnlen(name, KSYM_NAME_LEN);
> +	
> +	if (n_len >= KSYM_NAME_LEN)
>  		return 0;

Isn't it possible to do this and not need __compiletime_strlen at all?

	n_len = strnlen(name, min(__member_size(name), KSYM_NAME_LEN));

?

>  	if (name[0] != '.') {
> -- 
> 2.51.0

-- 
Kees Cook