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

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Message-Id: <20250724-pinctrl-gpio-pinfuncs-v3-1-af4db9302de4@linaro.org>
Date: Thu, 24 Jul 2025 11:24:29 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: 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>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.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>
Cc: 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: [PATCH v3 01/15] lib: provide kmemdup_const()

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>
---
 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);
 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