Accessing Userspace Memory (Slideshow)¶

Address Spaces ¶

User Address Space

MMU programmed (configured) per-process
Context switch includes re-programming MMU
⟶ Memory access violations

Kernel Address Space

Kernel can see all memory
Userspace addresses?

Copying To and From Userspace ¶

#include <linux/uaccess.h>

unsigned long copy_to_user(void __user * to,
                           const void * from,
                           unsigned long n);
unsigned long copy_from_user(void * to,
                             const void __user * from,
                             unsigned long n);

Returns number of bytes not transferred ⟶ 0 is ok
Usually used directly in ioctl() implementation
- ⟶ return -EFAULT when soemthing has not been transferred
- ⟶ Calling process segfaults

Documentation ¶