linux_kernel/arch/x86/lib/usercopy.c

/*
 * User address space access functions.
 *
 *  For licencing details see kernel-base/COPYING
 */

#include <linux/highmem.h>
#include <linux/export.h>

#include <asm/word-at-a-time.h>
#include <linux/sched.h>

/*
 * We rely on the nested NMI work to allow atomic faults from the NMI path; the
 * nested NMI paths are careful to preserve CR2.
 */
unsigned long
copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
{
	unsigned long ret;

	if (__range_not_ok(from, n, TASK_SIZE))
		return n;

	/*
	 * Even though this function is typically called from NMI/IRQ context
	 * disable pagefaults so that its behaviour is consistent even when
	 * called form other contexts.
	 */
	pagefault_disable();
	ret = __copy_from_user_inatomic(to, from, n);
	pagefault_enable();

	return ret;
}
EXPORT_SYMBOL_GPL(copy_from_user_nmi);

/**
 * copy_to_user: - Copy a block of data into user space.
 * @to:   Destination address, in user space.
 * @from: Source address, in kernel space.
 * @n:    Number of bytes to copy.
 *
 * Context: User context only. This function may sleep if pagefaults are
 *          enabled.
 *
 * Copy data from kernel space to user space.
 *
 * Returns number of bytes that could not be copied.
 * On success, this will be zero.
 */
unsigned long _copy_to_user(void __user *to, const void *from, unsigned n)
{
	if (access_ok(VERIFY_WRITE, to, n))
		n = __copy_to_user(to, from, n);
	return n;
}
EXPORT_SYMBOL(_copy_to_user);

/**
 * copy_from_user: - Copy a block of data from user space.
 * @to:   Destination address, in kernel space.
 * @from: Source address, in user space.
 * @n:    Number of bytes to copy.
 *
 * Context: User context only. This function may sleep if pagefaults are
 *          enabled.
 *
 * Copy data from user space to kernel space.
 *
 * Returns number of bytes that could not be copied.
 * On success, this will be zero.
 *
 * If some data could not be copied, this function will pad the copied
 * data to the requested size using zero bytes.
 */
unsigned long _copy_from_user(void *to, const void __user *from, unsigned n)
{
	if (access_ok(VERIFY_READ, from, n))
		n = __copy_from_user(to, from, n);
	else
		memset(to, 0, n);
	return n;
}
EXPORT_SYMBOL(_copy_from_user);