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, 96 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-88pm886.c b/drivers/rtc/rtc-88pm886.c
new file mode 100644
index 000000000..71443ae1b
--- /dev/null
+++ b/drivers/rtc/rtc-88pm886.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/limits.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+#include <linux/mfd/88pm886.h>
+
+/*
+ * Time is calculated as the sum of a 32-bit read-only advancing counter and a
+ * writeable constant offset stored in the chip's spare registers.
+ */
+
+static int pm886_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct regmap *regmap = dev_get_drvdata(dev);
+	u32 time;
+	u32 buf;
+	int ret;
+
+	ret = regmap_bulk_read(regmap, PM886_REG_RTC_SPARE1, &buf, 4);
+	if (ret)
+		return ret;
+	time = buf;
+
+	ret = regmap_bulk_read(regmap, PM886_REG_RTC_CNT1, &buf, 4);
+	if (ret)
+		return ret;
+	time += buf;
+
+	rtc_time64_to_tm(time, tm);
+
+	return 0;
+}
+
+static int pm886_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct regmap *regmap = dev_get_drvdata(dev);
+	u32 buf;
+	int ret;
+
+	ret = regmap_bulk_read(regmap, PM886_REG_RTC_CNT1, &buf, 4);
+	if (ret)
+		return ret;
+
+	buf = rtc_tm_to_time64(tm) - buf;
+
+	return regmap_bulk_write(regmap, PM886_REG_RTC_SPARE1, &buf, 4);
+}
+
+static const struct rtc_class_ops pm886_rtc_ops = {
+	.read_time = pm886_rtc_read_time,
+	.set_time = pm886_rtc_set_time,
+};
+
+static int pm886_rtc_probe(struct platform_device *pdev)
+{
+	struct pm886_chip *chip = dev_get_drvdata(pdev->dev.parent);
+	struct device *dev = &pdev->dev;
+	struct rtc_device *rtc;
+	int ret;
+
+	platform_set_drvdata(pdev, chip->regmap);
+
+	rtc = devm_rtc_allocate_device(dev);
+	if (IS_ERR(rtc))
+		return dev_err_probe(dev, PTR_ERR(rtc),
+				"Failed to allocate RTC device\n");
+
+	rtc->ops = &pm886_rtc_ops;
+	rtc->range_max = U32_MAX;
+
+	ret = devm_rtc_register_device(rtc);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to register RTC device\n");
+
+	return 0;
+}
+
+static const struct platform_device_id pm886_rtc_id_table[] = {
+	{ .name = "88pm886-rtc" },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, pm886_rtc_id_table);
+
+static struct platform_driver pm886_rtc_driver = {
+	.driver = {
+		.name = "88pm886-rtc",
+	},
+	.probe = pm886_rtc_probe,
+	.id_table = pm886_rtc_id_table,
+};
+module_platform_driver(pm886_rtc_driver);
+
+MODULE_DESCRIPTION("Marvell 88PM886 RTC driver");
+MODULE_AUTHOR("Karel Balej <balejk@matfyz.cz>");
+MODULE_LICENSE("GPL");