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[S390] maccess: arch specific probe_kernel_write() implementation

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Add an s390 specific probe_kernel_write() function which allows to
write to the kernel text segment even if write protection is enabled.
This is implemented using the lra (load real address) and stura (store
using real address) instructions.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Heiko Carstens 2009-06-12 10:26:42 +02:00 committed by Martin Schwidefsky
parent d93f82b6e0
commit 88df125fd6
2 changed files with 62 additions and 1 deletions
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2
arch/s390/mm/Makefile
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@ -2,7 +2,7 @@
# Makefile for the linux s390-specific parts of the memory manager.
#
obj-y := init.o fault.o extmem.o mmap.o vmem.o pgtable.o
obj-y := init.o fault.o extmem.o mmap.o vmem.o pgtable.o maccess.o
obj-$(CONFIG_CMM) += cmm.o
obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
obj-$(CONFIG_PAGE_STATES) += page-states.o

61
arch/s390/mm/maccess.c Normal file
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@ -0,0 +1,61 @@
/*
* 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;
}