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, 31 insertions, 0 deletions

diff --git a/drivers/rtc/nvmem.c b/drivers/rtc/nvmem.c
new file mode 100644
index 000000000..37df7e805
--- /dev/null
+++ b/drivers/rtc/nvmem.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * RTC subsystem, nvmem interface
+ *
+ * Copyright (C) 2017 Alexandre Belloni
+ */
+
+#include <linux/err.h>
+#include <linux/types.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/rtc.h>
+
+int devm_rtc_nvmem_register(struct rtc_device *rtc,
+		       struct nvmem_config *nvmem_config)
+{
+	struct device *dev = rtc->dev.parent;
+	struct nvmem_device *nvmem;
+
+	if (!nvmem_config)
+		return -ENODEV;
+
+	nvmem_config->dev = dev;
+	nvmem_config->owner = rtc->owner;
+	nvmem_config->add_legacy_fixed_of_cells = true;
+	nvmem = devm_nvmem_register(dev, nvmem_config);
+	if (IS_ERR(nvmem))
+		dev_err(dev, "failed to register nvmem device for RTC\n");
+
+	return PTR_ERR_OR_ZERO(nvmem);
+}
+EXPORT_SYMBOL_GPL(devm_rtc_nvmem_register);