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, 58 insertions, 0 deletions

diff --git a/drivers/misc/ibmasm/uart.c b/drivers/misc/ibmasm/uart.c
new file mode 100644
index 000000000..a5d4c8e01
--- /dev/null
+++ b/drivers/misc/ibmasm/uart.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * IBM ASM Service Processor Device Driver
+ *
+ * Copyright (C) IBM Corporation, 2004
+ *
+ * Author: Max Asböck <amax@us.ibm.com>
+ */
+
+#include <linux/termios.h>
+#include <linux/tty.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+#include <linux/serial_8250.h>
+#include "ibmasm.h"
+#include "lowlevel.h"
+
+
+void ibmasm_register_uart(struct service_processor *sp)
+{
+	struct uart_8250_port uart;
+	void __iomem *iomem_base;
+
+	iomem_base = sp->base_address + SCOUT_COM_B_BASE;
+
+	/* read the uart scratch register to determine if the UART
+	 * is dedicated to the service processor or if the OS can use it
+	 */
+	if (0 == readl(iomem_base + UART_SCR)) {
+		dev_info(sp->dev, "IBM SP UART not registered, owned by service processor\n");
+		sp->serial_line = -1;
+		return;
+	}
+
+	memset(&uart, 0, sizeof(uart));
+	uart.port.irq		= sp->irq;
+	uart.port.uartclk	= 3686400;
+	uart.port.flags		= UPF_SHARE_IRQ;
+	uart.port.iotype	= UPIO_MEM;
+	uart.port.membase	= iomem_base;
+
+	sp->serial_line = serial8250_register_8250_port(&uart);
+	if (sp->serial_line < 0) {
+		dev_err(sp->dev, "Failed to register serial port\n");
+		return;
+	}
+	enable_uart_interrupts(sp->base_address);
+}
+
+void ibmasm_unregister_uart(struct service_processor *sp)
+{
+	if (sp->serial_line < 0)
+		return;
+
+	disable_uart_interrupts(sp->base_address);
+	serial8250_unregister_port(sp->serial_line);
+}