linux-hardening - Re: [PATCH v3 01/15] lib: provide kmemdup

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Message-ID: <e1253b8a-4940-417f-b530-09e57c6a8932@lucifer.local>
Date: Thu, 24 Jul 2025 12:09:37 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Linus Walleij <linus.walleij@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Alexey Klimov <alexey.klimov@...aro.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Sean Wang <sean.wang@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
        Paul Cercueil <paul@...pouillou.net>, Kees Cook <kees@...nel.org>,
        Andy Shevchenko <andy@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Dong Aisheng <aisheng.dong@....com>,
        Fabio Estevam <festevam@...il.com>, Shawn Guo <shawnguo@...nel.org>,
        Jacky Bai <ping.bai@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP S32 Linux Team <s32@....com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Tony Lindgren <tony@...mide.com>,
        Haojian Zhuang <haojian.zhuang@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-mm@...ck.org,
        imx@...ts.linux.dev, linux-omap@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 01/15] lib: provide kmemdup_const()

On Thu, Jul 24, 2025 at 11:24:29AM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.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@...aro.org>

LGTM afaict aside from nit below, so:

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