Broadcasting the Linux kernel, one source file at a time!

mm/maccess.c

mm/maccess.c (62 lines, 1671 bytes)
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/*
 * Access kernel memory without faulting.
 */
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/uaccess.h>

/**
 * probe_kernel_read(): safely attempt to read from a location
 * @dst: pointer to the buffer that shall take the data
 * @src: address to read from
 * @size: size of the data chunk
 *
 * Safely read from address @src to the buffer at @dst.  If a kernel fault
 * happens, handle that and return -EFAULT.
 */

long __weak probe_kernel_read(void *dst, const void *src, size_t size)
    __attribute__((alias("__probe_kernel_read")));

long __probe_kernel_read(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_from_user_inatomic(dst,
          (__force const void __user *)src, size);
  pagefault_enable();
  set_fs(old_fs);

  return ret ? -EFAULT : 0;
}
EXPORT_SYMBOL_GPL(probe_kernel_read);

/**
 * probe_kernel_write(): 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 __weak probe_kernel_write(void *dst, const void *src, size_t size)
    __attribute__((alias("__probe_kernel_write")));

long __probe_kernel_write(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);

  return ret ? -EFAULT : 0;
}
EXPORT_SYMBOL_GPL(probe_kernel_write);