[PATCH v2] mm: new primitive kvmemdup()

[Hao Sun]

Similar to kmemdup(), but support large amount of bytes with kvmalloc()
and does *not* guarantee that the result will be physically contiguous.
Use only in cases where kvmalloc() is needed and free it with kvfree().
Also adapt policy_unpack.c in case someone bisect into this.

Suggested-by: Daniel Borkmann <daniel at iogearbox.net>
Signed-off-by: Hao Sun <sunhao.th at gmail.com>
---
This pattern has been used in several places and we're also going to
do this[1], seems reasonable to add this so that bpf and in future
others could make use of it.

v1 -> v2 adapt policy_unpack.c to fix compile error

[1] https://lore.kernel.org/bpf/7d274284-0fcc-061c-582e-3dfb629c6a44@iogearbox.net/T/#t
---
 include/linux/string.h            |  1 +
 mm/util.c                         | 24 +++++++++++++++++++++++-
 security/apparmor/policy_unpack.c | 11 +----------
 3 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index db28802ab0a6..c062c581a98b 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -177,6 +177,7 @@ extern char *kstrdup(const char *s, gfp_t gfp) __malloc;
 extern const char *kstrdup_const(const char *s, gfp_t gfp);
 extern char *kstrndup(const char *s, size_t len, gfp_t gfp);
 extern void *kmemdup(const void *src, size_t len, gfp_t gfp) __realloc_size(2);
+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 char **argv_split(gfp_t gfp, const char *str, int *argcp);
diff --git a/mm/util.c b/mm/util.c
index b56c92fb910f..cec9327b27b4 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -120,7 +120,8 @@ EXPORT_SYMBOL(kstrndup);
  * @len: memory region length
  * @gfp: GFP mask to use
  *
- * Return: newly allocated copy of @src or %NULL in case of error
+ * Return: newly allocated copy of @src or %NULL in case of error,
+ * result is physically contiguous. Use kfree() to free.
  */
 void *kmemdup(const void *src, size_t len, gfp_t gfp)
 {
@@ -133,6 +134,27 @@ void *kmemdup(const void *src, size_t len, gfp_t gfp)
 }
 EXPORT_SYMBOL(kmemdup);
 
+/**
+ * kvmemdup - duplicate region of memory
+ *
+ * @src: memory region to duplicate
+ * @len: memory region length
+ * @gfp: GFP mask to use
+ *
+ * Return: newly allocated copy of @src or %NULL in case of error,
+ * result may be not physically contiguous. Use kvfree() to free.
+ */
+void *kvmemdup(const void *src, size_t len, gfp_t gfp)
+{
+	void *p;
+
+	p = kvmalloc(len, gfp);
+	if (p)
+		memcpy(p, src, len);
+	return p;
+}
+EXPORT_SYMBOL(kvmemdup);
+
 /**
  * kmemdup_nul - Create a NUL-terminated string from unterminated data
  * @s: The data to stringify
diff --git a/security/apparmor/policy_unpack.c b/security/apparmor/policy_unpack.c
index 66915653108c..5e9949832af6 100644
--- a/security/apparmor/policy_unpack.c
+++ b/security/apparmor/policy_unpack.c
@@ -161,15 +161,6 @@ VISIBLE_IF_KUNIT bool aa_inbounds(struct aa_ext *e, size_t size)
 }
 EXPORT_SYMBOL_IF_KUNIT(aa_inbounds);
 
-static void *kvmemdup(const void *src, size_t len)
-{
-	void *p = kvmalloc(len, GFP_KERNEL);
-
-	if (p)
-		memcpy(p, src, len);
-	return p;
-}
-
 /**
  * aa_unpack_u16_chunk - test and do bounds checking for a u16 size based chunk
  * @e: serialized data read head (NOT NULL)
@@ -1027,7 +1018,7 @@ static struct aa_profile *unpack_profile(struct aa_ext *e, char **ns_name)
 
 			data->key = key;
 			data->size = aa_unpack_blob(e, &data->data, NULL);
-			data->data = kvmemdup(data->data, data->size);
+			data->data = kvmemdup(data->data, data->size, GFP_KERNEL);
 			if (data->size && !data->data) {
 				kfree_sensitive(data->key);
 				kfree_sensitive(data);

base-commit: b6bb9676f2165d518b35ba3bea5f1fcfc0d969bf
-- 
2.39.0