arch/s390/mm/maccess.c

   1 /*
   2  * Access kernel memory without faulting -- s390 specific implementation.
   3  *
   4  * Copyright IBM Corp. 2009
   5  *
   6  *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
   7  *
   8  */
   9
  10 #include <linux/uaccess.h>
  11 #include <linux/kernel.h>
  12 #include <linux/types.h>
  13 #include <linux/errno.h>
  14 #include <asm/system.h>
  15
  16 /*
  17  * This function writes to kernel memory bypassing DAT and possible
  18  * write protection. It copies one to four bytes from src to dst
  19  * using the stura instruction.
  20  * Returns the number of bytes copied or -EFAULT.
  21  */
  22 static long probe_kernel_write_odd(void *dst, void *src, size_t size)
  23 {
  24         unsigned long count, aligned;
  25         int offset, mask;
  26         int rc = -EFAULT;
  27
  28         aligned = (unsigned long) dst & ~3UL;
  29         offset = (unsigned long) dst & 3;
  30         count = min_t(unsigned long, 4 - offset, size);
  31         mask = (0xf << (4 - count)) & 0xf;
  32         mask >>= offset;
  33         asm volatile(
  34                 "       bras    1,0f\n"
  35                 "       icm     0,0,0(%3)\n"
  36                 "0:     l       0,0(%1)\n"
  37                 "       lra     %1,0(%1)\n"
  38                 "1:     ex      %2,0(1)\n"
  39                 "2:     stura   0,%1\n"
  40                 "       la      %0,0\n"
  41                 "3:\n"
  42                 EX_TABLE(0b,3b) EX_TABLE(1b,3b) EX_TABLE(2b,3b)
  43                 : "+d" (rc), "+a" (aligned)
  44                 : "a" (mask), "a" (src) : "cc", "memory", "0", "1");
  45         return rc ? rc : count;
  46 }
  47
  48 long probe_kernel_write(void *dst, void *src, size_t size)
  49 {
  50         long copied = 0;
  51
  52         while (size) {
  53                 copied = probe_kernel_write_odd(dst, src, size);
  54                 if (copied < 0)
  55                         break;
  56                 dst += copied;
  57                 src += copied;
  58                 size -= copied;
  59         }
  60         return copied < 0 ? -EFAULT : 0;
  61 }