/*
* Access kernel memory without faulting -- s390 specific implementation.
*
* Copyright IBM Corp. 2009
*
* Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
*
*/
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <asm/system.h>
/*
* This function writes to kernel memory bypassing DAT and possible
* write protection. It copies one to four bytes from src to dst
* using the stura instruction.
* Returns the number of bytes copied or -EFAULT.
*/
static long probe_kernel_write_odd(void *dst, void *src, size_t size)
{
unsigned long count, aligned;
int offset, mask;
int rc = -EFAULT;
aligned = (unsigned long) dst & ~3UL;
offset = (unsigned long) dst & 3;
count = min_t(unsigned long, 4 - offset, size);
mask = (0xf << (4 - count)) & 0xf;
mask >>= offset;
asm volatile(
" bras 1,0f\n"
" icm 0,0,0(%3)\n"
"0: l 0,0(%1)\n"
" lra %1,0(%1)\n"
"1: ex %2,0(1)\n"
"2: stura 0,%1\n"
" la %0,0\n"
"3:\n"
EX_TABLE(0b,3b) EX_TABLE(1b,3b) EX_TABLE(2b,3b)
: "+d" (rc), "+a" (aligned)
: "a" (mask), "a" (src) : "cc", "memory", "0", "1");
return rc ? rc : count;
}
long probe_kernel_write(void *dst, void *src, size_t size)
{
long copied = 0;
while (size) {
copied = probe_kernel_write_odd(dst, src, size);
if (copied < 0)
break;
dst += copied;
src += copied;
size -= copied;
}
return copied < 0 ? -EFAULT : 0;
}
