From 88df125fd6127e409793fd84a574566651450320 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Fri, 12 Jun 2009 10:26:42 +0200
Subject: [PATCH] [S390] maccess: arch specific probe_kernel_write()
 implementation

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>
---
 arch/s390/mm/Makefile  |  2 +-
 arch/s390/mm/maccess.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 arch/s390/mm/maccess.c

diff --git a/arch/s390/mm/Makefile b/arch/s390/mm/Makefile
index 2a745813454..db05661ac89 100644
--- a/arch/s390/mm/Makefile
+++ b/arch/s390/mm/Makefile
@@ -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
diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
new file mode 100644
index 00000000000..81756271dc4
--- /dev/null
+++ b/arch/s390/mm/maccess.c
@@ -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;
+}
-- 
2.11.4.GIT