[RFC PATCH v1 1/9] uaccess: Split check_zeroed_user() out of usercopy.c

Christophe Leroy (CS GROUP)
2026-04-27T17:17:21Z

Until commit f5a1a536fa14 ("lib: introduce copy_struct_from_user()
helper"), lib/usercopy.c was containing only the out-line version
of user copy fonctions.

That commit added function check_zeroed_user() into the same file.
Move that function into a new file named usercheck.c, so that next
patch can change usercopy.c build to a conditional build.

Signed-off-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
---
lib/Makefile | 1 +
lib/{usercopy.c => usercheck.c} | 22 ------------
lib/usercopy.c | 62 ---------------------------------
3 files changed, 1 insertion(+), 84 deletions(-)
copy lib/{usercopy.c => usercheck.c} (73%)

diff --git a/lib/Makefile b/lib/Makefile
index f33a24bf1c19..7c0334d7675b 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -59,6 +59,7 @@ obj-y += bcd.o sort.o parser.o debug_locks.o random32.o \
percpu-refcount.o rhashtable.o base64.o \
once.o refcount.o rcuref.o usercopy.o errseq.o bucket_locks.o \
generic-radix-tree.o bitmap-str.o
+obj-y += usercheck.o
obj-y += string_helpers.o
obj-y += hexdump.o
obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
diff --git a/lib/usercopy.c b/lib/usercheck.c
similarity index 73%
copy from lib/usercopy.c
copy to lib/usercheck.c
index b00a3a957de6..15b0d9a18435 100644
--- a/lib/usercopy.c
+++ b/lib/usercheck.c
@@ -2,32 +2,10 @@
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/export.h>
-#include <linux/fault-inject-usercopy.h>
-#include <linux/instrumented.h>
#include <linux/kernel.h>
-#include <linux/nospec.h>
-#include <linux/string.h>
#include <linux/uaccess.h>
#include <linux/wordpart.h>

-/* out-of-line parts */
-
-#if !defined(INLINE_COPY_FROM_USER)
-unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
-{
- return _inline_copy_from_user(to, from, n);
-}
-EXPORT_SYMBOL(_copy_from_user);
-#endif
-
-#if !defined(INLINE_COPY_TO_USER)
-unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
-{
- return _inline_copy_to_user(to, from, n);
-}
-EXPORT_SYMBOL(_copy_to_user);
-#endif
-
/**
* check_zeroed_user: check if a userspace buffer only contains zero bytes
* @from: Source address, in userspace.
diff --git a/lib/usercopy.c b/lib/usercopy.c
index b00a3a957de6..7a93f56d81dd 100644
--- a/lib/usercopy.c
+++ b/lib/usercopy.c
@@ -1,14 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
-#include <linux/compiler.h>
-#include <linux/errno.h>
#include <linux/export.h>
-#include <linux/fault-inject-usercopy.h>
-#include <linux/instrumented.h>
-#include <linux/kernel.h>
-#include <linux/nospec.h>
-#include <linux/string.h>
#include <linux/uaccess.h>
-#include <linux/wordpart.h>

/* out-of-line parts */

@@ -27,57 +19,3 @@ unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
}
EXPORT_SYMBOL(_copy_to_user);
#endif
-
-/**
- * check_zeroed_user: check if a userspace buffer only contains zero bytes
- * @from: Source address, in userspace.
- * @size: Size of buffer.
- *
- * This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for
- * userspace addresses (and is more efficient because we don't care where the
- * first non-zero byte is).
- *
- * Returns:
- * * 0: There were non-zero bytes present in the buffer.
- * * 1: The buffer was full of zero bytes.
- * * -EFAULT: access to userspace failed.
- */
-int check_zeroed_user(const void __user *from, size_t size)
-{
- unsigned long val;
- uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
-
- if (unlikely(size == 0))
- return 1;
-
- from -= align;
- size += align;
-
- if (!user_read_access_begin(from, size))
- return -EFAULT;
-
- unsafe_get_user(val, (unsigned long __user *) from, err_fault);
- if (align)
- val &= ~aligned_byte_mask(align);
-
- while (size > sizeof(unsigned long)) {
- if (unlikely(val))
- goto done;
-
- from += sizeof(unsigned long);
- size -= sizeof(unsigned long);
-
- unsafe_get_user(val, (unsigned long __user *) from, err_fault);
- }
-
- if (size < sizeof(unsigned long))
- val &= aligned_byte_mask(size);
-
-done:
- user_read_access_end();
- return (val == 0);
-err_fault:
- user_read_access_end();
- return -EFAULT;
-}
-EXPORT_SYMBOL(check_zeroed_user);
--
2.49.0