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, 98 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-sun4v.c b/drivers/rtc/rtc-sun4v.c
new file mode 100644
index 000000000..a86e27de8
--- /dev/null
+++ b/drivers/rtc/rtc-sun4v.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+/* rtc-sun4v.c: Hypervisor based RTC for SUN4V systems.
+ *
+ * Author: David S. Miller
+ *
+ * Copyright (C) 2008 David S. Miller <davem@davemloft.net>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+
+#include <asm/hypervisor.h>
+
+static unsigned long hypervisor_get_time(void)
+{
+	unsigned long ret, time;
+	int retries = 10000;
+
+retry:
+	ret = sun4v_tod_get(&time);
+	if (ret == HV_EOK)
+		return time;
+	if (ret == HV_EWOULDBLOCK) {
+		if (--retries > 0) {
+			udelay(100);
+			goto retry;
+		}
+		pr_warn("tod_get() timed out.\n");
+		return 0;
+	}
+	pr_warn("tod_get() not supported.\n");
+	return 0;
+}
+
+static int sun4v_read_time(struct device *dev, struct rtc_time *tm)
+{
+	rtc_time64_to_tm(hypervisor_get_time(), tm);
+	return 0;
+}
+
+static int hypervisor_set_time(unsigned long secs)
+{
+	unsigned long ret;
+	int retries = 10000;
+
+retry:
+	ret = sun4v_tod_set(secs);
+	if (ret == HV_EOK)
+		return 0;
+	if (ret == HV_EWOULDBLOCK) {
+		if (--retries > 0) {
+			udelay(100);
+			goto retry;
+		}
+		pr_warn("tod_set() timed out.\n");
+		return -EAGAIN;
+	}
+	pr_warn("tod_set() not supported.\n");
+	return -EOPNOTSUPP;
+}
+
+static int sun4v_set_time(struct device *dev, struct rtc_time *tm)
+{
+	return hypervisor_set_time(rtc_tm_to_time64(tm));
+}
+
+static const struct rtc_class_ops sun4v_rtc_ops = {
+	.read_time	= sun4v_read_time,
+	.set_time	= sun4v_set_time,
+};
+
+static int __init sun4v_rtc_probe(struct platform_device *pdev)
+{
+	struct rtc_device *rtc;
+
+	rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	rtc->ops = &sun4v_rtc_ops;
+	rtc->range_max = U64_MAX;
+	platform_set_drvdata(pdev, rtc);
+
+	return devm_rtc_register_device(rtc);
+}
+
+static struct platform_driver sun4v_rtc_driver = {
+	.driver		= {
+		.name	= "rtc-sun4v",
+	},
+};
+
+builtin_platform_driver_probe(sun4v_rtc_driver, sun4v_rtc_probe);