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, 111 insertions, 0 deletions

diff --git a/block/partitions/of.c b/block/partitions/of.c
new file mode 100644
index 000000000..53664ea06
--- /dev/null
+++ b/block/partitions/of.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/blkdev.h>
+#include <linux/major.h>
+#include <linux/of.h>
+#include <linux/string.h>
+#include "check.h"
+
+static int validate_of_partition(struct device_node *np, int slot)
+{
+	u64 offset, size;
+	int len;
+
+	const __be32 *reg = of_get_property(np, "reg", &len);
+	int a_cells = of_n_addr_cells(np);
+	int s_cells = of_n_size_cells(np);
+
+	/* Make sure reg len match the expected addr and size cells */
+	if (len / sizeof(*reg) != a_cells + s_cells)
+		return -EINVAL;
+
+	/* Validate offset conversion from bytes to sectors */
+	offset = of_read_number(reg, a_cells);
+	if (offset % SECTOR_SIZE)
+		return -EINVAL;
+
+	/* Validate size conversion from bytes to sectors */
+	size = of_read_number(reg + a_cells, s_cells);
+	if (!size || size % SECTOR_SIZE)
+		return -EINVAL;
+
+	return 0;
+}
+
+static void add_of_partition(struct parsed_partitions *state, int slot,
+			     struct device_node *np)
+{
+	struct partition_meta_info *info;
+	const char *partname;
+	int len;
+
+	const __be32 *reg = of_get_property(np, "reg", &len);
+	int a_cells = of_n_addr_cells(np);
+	int s_cells = of_n_size_cells(np);
+
+	/* Convert bytes to sector size */
+	u64 offset = of_read_number(reg, a_cells) / SECTOR_SIZE;
+	u64 size = of_read_number(reg + a_cells, s_cells) / SECTOR_SIZE;
+
+	put_partition(state, slot, offset, size);
+
+	if (of_property_read_bool(np, "read-only"))
+		state->parts[slot].flags |= ADDPART_FLAG_READONLY;
+
+	/*
+	 * Follow MTD label logic, search for label property,
+	 * fallback to node name if not found.
+	 */
+	info = &state->parts[slot].info;
+	partname = of_get_property(np, "label", &len);
+	if (!partname)
+		partname = of_get_property(np, "name", &len);
+	strscpy(info->volname, partname, sizeof(info->volname));
+
+	seq_buf_printf(&state->pp_buf, "(%s)", info->volname);
+}
+
+int of_partition(struct parsed_partitions *state)
+{
+	struct device *ddev = disk_to_dev(state->disk);
+	struct device_node *np;
+	int slot;
+
+	struct device_node *partitions_np = of_node_get(ddev->of_node);
+
+	if (!partitions_np ||
+	    !of_device_is_compatible(partitions_np, "fixed-partitions")) {
+		of_node_put(partitions_np);
+		return 0;
+	}
+
+	slot = 1;
+	/* Validate parition offset and size */
+	for_each_child_of_node(partitions_np, np) {
+		if (validate_of_partition(np, slot)) {
+			of_node_put(np);
+			of_node_put(partitions_np);
+
+			return -1;
+		}
+
+		slot++;
+	}
+
+	slot = 1;
+	for_each_child_of_node(partitions_np, np) {
+		if (slot >= state->limit) {
+			of_node_put(np);
+			break;
+		}
+
+		add_of_partition(state, slot, np);
+
+		slot++;
+	}
+
+	seq_buf_puts(&state->pp_buf, "\n");
+
+	of_node_put(partitions_np);
+	return 1;
+}