Re: [PATCH v3 01/15] lib: provide kmemdup_const()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Thu, Jul 24, 2025 at 11:24:29AM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> Provide a function similar to strdup_const() but for copying blocks of
> memory that are likely to be placed in .rodata.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

LGTM afaict aside from nit below, so:

Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  include/linux/string.h |  1 +
>  mm/util.c              | 21 +++++++++++++++++++++
>  2 files changed, 22 insertions(+)
>
> diff --git a/include/linux/string.h b/include/linux/string.h
> index fdd3442c6bcbd786e177b6e87358e1065a0ffafc..1a86d61de91204563e4179938c4dfc77108e03aa 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -304,6 +304,7 @@ extern char *kstrndup(const char *s, size_t len, gfp_t gfp);
>  extern void *kmemdup_noprof(const void *src, size_t len, gfp_t gfp) __realloc_size(2);
>  #define kmemdup(...)	alloc_hooks(kmemdup_noprof(__VA_ARGS__))
>
> +extern const void *kmemdup_const(const void *src, size_t len, gfp_t gfp);

Please drop extern, it's unnecessary.

>  extern void *kvmemdup(const void *src, size_t len, gfp_t gfp) __realloc_size(2);
>  extern char *kmemdup_nul(const char *s, size_t len, gfp_t gfp);
>  extern void *kmemdup_array(const void *src, size_t count, size_t element_size, gfp_t gfp)
> diff --git a/mm/util.c b/mm/util.c
> index f814e6a59ab1d354b8cd04ebf3903626f6b23a6c..f4df9194b0c69c27ff06e6ba1d1137c559035470 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -142,6 +142,27 @@ void *kmemdup_noprof(const void *src, size_t len, gfp_t gfp)
>  }
>  EXPORT_SYMBOL(kmemdup_noprof);
>
> +/**
> + * kmemdup_const - conditionally duplicate a region of memory
> + *
> + * @src: memory region to duplicate
> + * @len: memory region length,
> + * @gfp: GFP mask to use
> + *
> + * Return: source address if it is in .rodata or the return value of kmemdup()
> + * to which the function falls back otherwise.
> + *
> + * Note: the returned address must not be passed to kfree(), the caller must
> + * use kfree_const() instead.
> + */
> +const void *kmemdup_const(const void *src, size_t len, gfp_t gfp)
> +{
> +	if (is_kernel_rodata((unsigned long)src))
> +		return src;
> +
> +	return kmemdup(src, len, gfp);
> +}
> +
>  /**
>   * kmemdup_array - duplicate a given array.
>   *
>
> --
> 2.48.1
>