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, 43 insertions, 0 deletions

diff --git a/arch/mips/dec/reset.c b/arch/mips/dec/reset.c
new file mode 100644
index 000000000..ee1ad38f4
--- /dev/null
+++ b/arch/mips/dec/reset.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Reset a DECstation machine.
+ *
+ * Copyright (C) 199x  the Anonymous
+ * Copyright (C) 2001, 2002, 2003  Maciej W. Rozycki
+ */
+#include <linux/interrupt.h>
+#include <linux/linkage.h>
+
+#include <asm/addrspace.h>
+
+#include <asm/dec/reset.h>
+
+typedef void __noreturn (* noret_func_t)(void);
+
+static inline void __noreturn back_to_prom(void)
+{
+	noret_func_t func = (void *)CKSEG1ADDR(0x1fc00000);
+
+	func();
+}
+
+void __noreturn dec_machine_restart(char *command)
+{
+	back_to_prom();
+}
+
+void __noreturn dec_machine_halt(void)
+{
+	back_to_prom();
+}
+
+void __noreturn dec_machine_power_off(void)
+{
+    /* DECstations don't have a software power switch */
+	back_to_prom();
+}
+
+irqreturn_t dec_intr_halt(int irq, void *dev_id)
+{
+	dec_machine_halt();
+}