openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 92 insertions, 0 deletions

diff --git a/arch/mips/dec/wbflush.c b/arch/mips/dec/wbflush.c
new file mode 100644
index 000000000..dad64d178
--- /dev/null
+++ b/arch/mips/dec/wbflush.c
@@ -0,0 +1,92 @@
+/*
+ * Setup the right wbflush routine for the different DECstations.
+ *
+ * Created with information from:
+ *	DECstation 3100 Desktop Workstation Functional Specification
+ *	DECstation 5000/200 KN02 System Module Functional Specification
+ *	mipsel-linux-objdump --disassemble vmunix | grep "wbflush" :-)
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 1998 Harald Koerfgen
+ * Copyright (C) 2002 Maciej W. Rozycki
+ */
+
+#include <linux/export.h>
+#include <linux/init.h>
+
+#include <asm/bootinfo.h>
+#include <asm/wbflush.h>
+#include <asm/barrier.h>
+
+static void wbflush_kn01(void);
+static void wbflush_kn210(void);
+static void wbflush_mips(void);
+
+void (*__wbflush) (void);
+
+void __init wbflush_setup(void)
+{
+	switch (mips_machtype) {
+	case MACH_DS23100:
+	case MACH_DS5000_200:	/* DS5000 3max */
+		__wbflush = wbflush_kn01;
+		break;
+	case MACH_DS5100:	/* DS5100 MIPSMATE */
+		__wbflush = wbflush_kn210;
+		break;
+	case MACH_DS5000_1XX:	/* DS5000/100 3min */
+	case MACH_DS5000_XX:	/* Personal DS5000/2x */
+	case MACH_DS5000_2X0:	/* DS5000/240 3max+ */
+	case MACH_DS5900:	/* DS5900 bigmax */
+	default:
+		__wbflush = wbflush_mips;
+		break;
+	}
+}
+
+/*
+ * For the DS3100 and DS5000/200 the R2020/R3220 writeback buffer functions
+ * as part of Coprocessor 0.
+ */
+static void wbflush_kn01(void)
+{
+    asm(".set\tpush\n\t"
+	".set\tnoreorder\n\t"
+	"1:\tbc0f\t1b\n\t"
+	"nop\n\t"
+	".set\tpop");
+}
+
+/*
+ * For the DS5100 the writeback buffer seems to be a part of Coprocessor 3.
+ * But CP3 has to enabled first.
+ */
+static void wbflush_kn210(void)
+{
+    asm(".set\tpush\n\t"
+	".set\tnoreorder\n\t"
+	"mfc0\t$2,$12\n\t"
+	"lui\t$3,0x8000\n\t"
+	"or\t$3,$2,$3\n\t"
+	"mtc0\t$3,$12\n\t"
+	"nop\n"
+	"1:\tbc3f\t1b\n\t"
+	"nop\n\t"
+	"mtc0\t$2,$12\n\t"
+	"nop\n\t"
+	".set\tpop"
+	: : : "$2", "$3");
+}
+
+/*
+ * I/O ASIC systems use a standard writeback buffer that gets flushed
+ * upon an uncached read.
+ */
+static void wbflush_mips(void)
+{
+	__fast_iob();
+}
+EXPORT_SYMBOL(__wbflush);