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, 49 insertions, 0 deletions

diff --git a/arch/m68k/coldfire/cache.c b/arch/m68k/coldfire/cache.c
new file mode 100644
index 000000000..98ee89b87
--- /dev/null
+++ b/arch/m68k/coldfire/cache.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+/***************************************************************************/
+
+/*
+ *	cache.c -- general ColdFire Cache maintenance code
+ *
+ *	Copyright (C) 2010, Greg Ungerer (gerg@snapgear.com)
+ */
+
+/***************************************************************************/
+
+#include <linux/kernel.h>
+#include <asm/coldfire.h>
+#include <asm/mcfsim.h>
+
+/***************************************************************************/
+#ifdef CACHE_PUSH
+/***************************************************************************/
+
+/*
+ *	Use cpushl to push all dirty cache lines back to memory.
+ *	Older versions of GAS don't seem to know how to generate the
+ *	ColdFire cpushl instruction... Oh well, bit stuff it for now.
+ */
+
+void mcf_cache_push(void)
+{
+	__asm__ __volatile__ (
+		"clrl	%%d0\n\t"
+		"1:\n\t"
+		"movel	%%d0,%%a0\n\t"
+		"2:\n\t"
+		".word	0xf468\n\t"
+		"addl	%0,%%a0\n\t"
+		"cmpl	%1,%%a0\n\t"
+		"blt	2b\n\t"
+		"addql	#1,%%d0\n\t"
+		"cmpil	%2,%%d0\n\t"
+		"bne	1b\n\t"
+		: /* No output */
+		: "i" (CACHE_LINE_SIZE),
+		  "i" (DCACHE_SIZE / CACHE_WAYS),
+		  "i" (CACHE_WAYS)
+		: "d0", "a0" );
+}
+
+/***************************************************************************/
+#endif /* CACHE_PUSH */
+/***************************************************************************/