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, 136 insertions, 0 deletions

diff --git a/drivers/firmware/google/cbmem.c b/drivers/firmware/google/cbmem.c
new file mode 100644
index 000000000..4d20477ed
--- /dev/null
+++ b/drivers/firmware/google/cbmem.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * cbmem.c
+ *
+ * Driver for exporting cbmem entries in sysfs.
+ *
+ * Copyright 2022 Google LLC
+ */
+
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/kobject.h>
+#include <linux/device-id/coreboot.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+
+#include "coreboot_table.h"
+
+struct cbmem_entry {
+	char *mem_file_buf;
+	u32 size;
+};
+
+static struct cbmem_entry *to_cbmem_entry(struct kobject *kobj)
+{
+	return dev_get_drvdata(kobj_to_dev(kobj));
+}
+
+static ssize_t mem_read(struct file *filp, struct kobject *kobj,
+			const struct bin_attribute *bin_attr, char *buf, loff_t pos,
+			size_t count)
+{
+	struct cbmem_entry *entry = to_cbmem_entry(kobj);
+
+	return memory_read_from_buffer(buf, count, &pos, entry->mem_file_buf,
+				       entry->size);
+}
+
+static ssize_t mem_write(struct file *filp, struct kobject *kobj,
+			 const struct bin_attribute *bin_attr, char *buf, loff_t pos,
+			 size_t count)
+{
+	struct cbmem_entry *entry = to_cbmem_entry(kobj);
+
+	if (pos < 0 || pos >= entry->size)
+		return -EINVAL;
+	if (count > entry->size - pos)
+		count = entry->size - pos;
+
+	memcpy(entry->mem_file_buf + pos, buf, count);
+	return count;
+}
+static const BIN_ATTR_ADMIN_RW(mem, 0);
+
+static ssize_t address_show(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	struct coreboot_device *cbdev = dev_to_coreboot_device(dev);
+
+	return sysfs_emit(buf, "0x%llx\n", cbdev->cbmem_entry.address);
+}
+static DEVICE_ATTR_RO(address);
+
+static ssize_t size_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct coreboot_device *cbdev = dev_to_coreboot_device(dev);
+
+	return sysfs_emit(buf, "0x%x\n", cbdev->cbmem_entry.entry_size);
+}
+static DEVICE_ATTR_RO(size);
+
+static struct attribute *attrs[] = {
+	&dev_attr_address.attr,
+	&dev_attr_size.attr,
+	NULL,
+};
+
+static const struct bin_attribute *const bin_attrs[] = {
+	&bin_attr_mem,
+	NULL,
+};
+
+static const struct attribute_group cbmem_entry_group = {
+	.attrs = attrs,
+	.bin_attrs = bin_attrs,
+};
+
+static const struct attribute_group *dev_groups[] = {
+	&cbmem_entry_group,
+	NULL,
+};
+
+static int cbmem_entry_probe(struct coreboot_device *dev)
+{
+	struct cbmem_entry *entry;
+
+	entry = devm_kzalloc(&dev->dev, sizeof(*entry), GFP_KERNEL);
+	if (!entry)
+		return -ENOMEM;
+
+	dev_set_drvdata(&dev->dev, entry);
+	entry->mem_file_buf = devm_memremap(&dev->dev, dev->cbmem_entry.address,
+					    dev->cbmem_entry.entry_size,
+					    MEMREMAP_WB);
+	if (IS_ERR(entry->mem_file_buf))
+		return PTR_ERR(entry->mem_file_buf);
+
+	entry->size = dev->cbmem_entry.entry_size;
+
+	return 0;
+}
+
+static const struct coreboot_device_id cbmem_ids[] = {
+	{ .tag = LB_TAG_CBMEM_ENTRY },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(coreboot, cbmem_ids);
+
+static struct coreboot_driver cbmem_entry_driver = {
+	.probe = cbmem_entry_probe,
+	.drv = {
+		.name = "cbmem",
+		.dev_groups = dev_groups,
+	},
+	.id_table = cbmem_ids,
+};
+module_coreboot_driver(cbmem_entry_driver);
+
+MODULE_AUTHOR("Jack Rosenthal <jrosenth@chromium.org>");
+MODULE_DESCRIPTION("Driver for exporting CBMEM entries in sysfs");
+MODULE_LICENSE("GPL");