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 protected]>
> ---
> 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
