// SPDX-License-Identifier: GPL-2.0-only
/*
 * Access kernel or user memory without faulting.
 */
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/uaccess.h>

bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
                size_t size)
{
        return true;
}

#ifdef HAVE_GET_KERNEL_NOFAULT

#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label)   \
        while (len >= sizeof(type)) {                                   \
                __get_kernel_nofault(dst, src, type, err_label);                \
                dst += sizeof(type);                                    \
                src += sizeof(type);                                    \
                len -= sizeof(type);                                    \
        }

long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
{
        if (!copy_from_kernel_nofault_allowed(src, size))
                return -ERANGE;

        pagefault_disable();
        copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
        copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
        copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
        copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
        pagefault_enable();
        return 0;
Efault:
        pagefault_enable();
        return -EFAULT;
}
EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);

#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label)     \
        while (len >= sizeof(type)) {                                   \
                __put_kernel_nofault(dst, src, type, err_label);                \
                dst += sizeof(type);                                    \
                src += sizeof(type);                                    \
                len -= sizeof(type);                                    \
        }

long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
        pagefault_disable();
        copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
        copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
        copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
        copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
        pagefault_enable();
        return 0;
Efault:
        pagefault_enable();
        return -EFAULT;
}

long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
{
        const void *src = unsafe_addr;

        if (unlikely(count <= 0))
                return 0;
        if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
                return -ERANGE;

        pagefault_disable();
        do {
                __get_kernel_nofault(dst, src, u8, Efault);
                dst++;
                src++;
        } while (dst[-1] && src - unsafe_addr < count);
        pagefault_enable();

        dst[-1] = '\0';
        return src - unsafe_addr;
Efault:
        pagefault_enable();
        dst[-1] = '\0';
        return -EFAULT;
}
#else /* HAVE_GET_KERNEL_NOFAULT */
/**
 * copy_from_kernel_nofault(): safely attempt to read from kernel-space
 * @dst: pointer to the buffer that shall take the data
 * @src: address to read from
 * @size: size of the data chunk
 *
 * Safely read from kernel address @src to the buffer at @dst.  If a kernel
 * fault happens, handle that and return -EFAULT.  If @src is not a valid kernel
 * address, return -ERANGE.
 *
 * We ensure that the copy_from_user is executed in atomic context so that
 * do_page_fault() doesn't attempt to take mmap_lock.  This makes
 * copy_from_kernel_nofault() suitable for use within regions where the caller
 * already holds mmap_lock, or other locks which nest inside mmap_lock.
 */
long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
{
        long ret;
        mm_segment_t old_fs = get_fs();

        if (!copy_from_kernel_nofault_allowed(src, size))
                return -ERANGE;

        set_fs(KERNEL_DS);
        pagefault_disable();
        ret = __copy_from_user_inatomic(dst, (__force const void __user *)src,
                        size);
        pagefault_enable();
        set_fs(old_fs);

        if (ret)
                return -EFAULT;
        return 0;
}
EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);

/**
 * copy_to_kernel_nofault(): safely attempt to write to a location
 * @dst: address to write to
 * @src: pointer to the data that shall be written
 * @size: size of the data chunk
 *
 * Safely write to address @dst from the buffer at @src.  If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
        long ret;
        mm_segment_t old_fs = get_fs();

        set_fs(KERNEL_DS);
        pagefault_disable();
        ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
        pagefault_enable();
        set_fs(old_fs);

        if (ret)
                return -EFAULT;
        return 0;
}

/**
 * strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe
 *                               address.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @unsafe_addr: Unsafe address.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from unsafe address to kernel buffer.
 *
 * On success, returns the length of the string INCLUDING the trailing NUL.
 *
 * If access fails, returns -EFAULT (some data may have been copied and the
 * trailing NUL added).  If @unsafe_addr is not a valid kernel address, return
 * -ERANGE.
 *
 * If @count is smaller than the length of the string, copies @count-1 bytes,
 * sets the last byte of @dst buffer to NUL and returns @count.
 */
long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
{
        mm_segment_t old_fs = get_fs();
        const void *src = unsafe_addr;
        long ret;

        if (unlikely(count <= 0))
                return 0;
        if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
                return -ERANGE;

        set_fs(KERNEL_DS);
        pagefault_disable();

        do {
                ret = __get_user(*dst++, (const char __user __force *)src++);
        } while (dst[-1] && ret == 0 && src - unsafe_addr < count);

        dst[-1] = '\0';
        pagefault_enable();
        set_fs(old_fs);

        return ret ? -EFAULT : src - unsafe_addr;
}
#endif /* HAVE_GET_KERNEL_NOFAULT */

/**
 * copy_from_user_nofault(): safely attempt to read from a user-space location
 * @dst: pointer to the buffer that shall take the data
 * @src: address to read from. This must be a user address.
 * @size: size of the data chunk
 *
 * Safely read from user address @src to the buffer at @dst. If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
{
        long ret = -EFAULT;
        mm_segment_t old_fs = force_uaccess_begin();

        if (access_ok(src, size)) {
                pagefault_disable();
                ret = __copy_from_user_inatomic(dst, src, size);
                pagefault_enable();
        }
        force_uaccess_end(old_fs);

        if (ret)
                return -EFAULT;
        return 0;
}
EXPORT_SYMBOL_GPL(copy_from_user_nofault);

/**
 * copy_to_user_nofault(): safely attempt to write to a user-space location
 * @dst: address to write to
 * @src: pointer to the data that shall be written
 * @size: size of the data chunk
 *
 * Safely write to address @dst from the buffer at @src.  If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_to_user_nofault(void __user *dst, const void *src, size_t size)
{
        long ret = -EFAULT;
        mm_segment_t old_fs = force_uaccess_begin();

        if (access_ok(dst, size)) {
                pagefault_disable();
                ret = __copy_to_user_inatomic(dst, src, size);
                pagefault_enable();
        }
        force_uaccess_end(old_fs);

        if (ret)
                return -EFAULT;
        return 0;
}
EXPORT_SYMBOL_GPL(copy_to_user_nofault);

/**
 * strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user
 *                              address.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @unsafe_addr: Unsafe user address.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from unsafe user address to kernel buffer.
 *
 * On success, returns the length of the string INCLUDING the trailing NUL.
 *
 * If access fails, returns -EFAULT (some data may have been copied
 * and the trailing NUL added).
 *
 * If @count is smaller than the length of the string, copies @count-1 bytes,
 * sets the last byte of @dst buffer to NUL and returns @count.
 */
long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
                              long count)
{
        mm_segment_t old_fs;
        long ret;

        if (unlikely(count <= 0))
                return 0;

        old_fs = force_uaccess_begin();
        pagefault_disable();
        ret = strncpy_from_user(dst, unsafe_addr, count);
        pagefault_enable();
        force_uaccess_end(old_fs);

        if (ret >= count) {
                ret = count;
                dst[ret - 1] = '\0';
        } else if (ret > 0) {
                ret++;
        }

        return ret;
}

/**
 * strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL.
 * @unsafe_addr: The string to measure.
 * @count: Maximum count (including NUL)
 *
 * Get the size of a NUL-terminated string in user space without pagefault.
 *
 * Returns the size of the string INCLUDING the terminating NUL.
 *
 * If the string is too long, returns a number larger than @count. User
 * has to check the return value against "> count".
 * On exception (or invalid count), returns 0.
 *
 * Unlike strnlen_user, this can be used from IRQ handler etc. because
 * it disables pagefaults.
 */
long strnlen_user_nofault(const void __user *unsafe_addr, long count)
{
        mm_segment_t old_fs;
        int ret;

        old_fs = force_uaccess_begin();
        pagefault_disable();
        ret = strnlen_user(unsafe_addr, count);
        pagefault_enable();
        force_uaccess_end(old_fs);

        return ret;
}