1*88df125fSHeiko Carstens /* 2*88df125fSHeiko Carstens * Access kernel memory without faulting -- s390 specific implementation. 3*88df125fSHeiko Carstens * 4*88df125fSHeiko Carstens * Copyright IBM Corp. 2009 5*88df125fSHeiko Carstens * 6*88df125fSHeiko Carstens * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>, 7*88df125fSHeiko Carstens * 8*88df125fSHeiko Carstens */ 9*88df125fSHeiko Carstens 10*88df125fSHeiko Carstens #include <linux/uaccess.h> 11*88df125fSHeiko Carstens #include <linux/kernel.h> 12*88df125fSHeiko Carstens #include <linux/types.h> 13*88df125fSHeiko Carstens #include <linux/errno.h> 14*88df125fSHeiko Carstens #include <asm/system.h> 15*88df125fSHeiko Carstens 16*88df125fSHeiko Carstens /* 17*88df125fSHeiko Carstens * This function writes to kernel memory bypassing DAT and possible 18*88df125fSHeiko Carstens * write protection. It copies one to four bytes from src to dst 19*88df125fSHeiko Carstens * using the stura instruction. 20*88df125fSHeiko Carstens * Returns the number of bytes copied or -EFAULT. 21*88df125fSHeiko Carstens */ 22*88df125fSHeiko Carstens static long probe_kernel_write_odd(void *dst, void *src, size_t size) 23*88df125fSHeiko Carstens { 24*88df125fSHeiko Carstens unsigned long count, aligned; 25*88df125fSHeiko Carstens int offset, mask; 26*88df125fSHeiko Carstens int rc = -EFAULT; 27*88df125fSHeiko Carstens 28*88df125fSHeiko Carstens aligned = (unsigned long) dst & ~3UL; 29*88df125fSHeiko Carstens offset = (unsigned long) dst & 3; 30*88df125fSHeiko Carstens count = min_t(unsigned long, 4 - offset, size); 31*88df125fSHeiko Carstens mask = (0xf << (4 - count)) & 0xf; 32*88df125fSHeiko Carstens mask >>= offset; 33*88df125fSHeiko Carstens asm volatile( 34*88df125fSHeiko Carstens " bras 1,0f\n" 35*88df125fSHeiko Carstens " icm 0,0,0(%3)\n" 36*88df125fSHeiko Carstens "0: l 0,0(%1)\n" 37*88df125fSHeiko Carstens " lra %1,0(%1)\n" 38*88df125fSHeiko Carstens "1: ex %2,0(1)\n" 39*88df125fSHeiko Carstens "2: stura 0,%1\n" 40*88df125fSHeiko Carstens " la %0,0\n" 41*88df125fSHeiko Carstens "3:\n" 42*88df125fSHeiko Carstens EX_TABLE(0b,3b) EX_TABLE(1b,3b) EX_TABLE(2b,3b) 43*88df125fSHeiko Carstens : "+d" (rc), "+a" (aligned) 44*88df125fSHeiko Carstens : "a" (mask), "a" (src) : "cc", "memory", "0", "1"); 45*88df125fSHeiko Carstens return rc ? rc : count; 46*88df125fSHeiko Carstens } 47*88df125fSHeiko Carstens 48*88df125fSHeiko Carstens long probe_kernel_write(void *dst, void *src, size_t size) 49*88df125fSHeiko Carstens { 50*88df125fSHeiko Carstens long copied = 0; 51*88df125fSHeiko Carstens 52*88df125fSHeiko Carstens while (size) { 53*88df125fSHeiko Carstens copied = probe_kernel_write_odd(dst, src, size); 54*88df125fSHeiko Carstens if (copied < 0) 55*88df125fSHeiko Carstens break; 56*88df125fSHeiko Carstens dst += copied; 57*88df125fSHeiko Carstens src += copied; 58*88df125fSHeiko Carstens size -= copied; 59*88df125fSHeiko Carstens } 60*88df125fSHeiko Carstens return copied < 0 ? -EFAULT : 0; 61*88df125fSHeiko Carstens } 62