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, 58 insertions, 0 deletions

diff --git a/drivers/nvmem/layouts/fixed-layout.c b/drivers/nvmem/layouts/fixed-layout.c
new file mode 100644
index 000000000..635d448b3
--- /dev/null
+++ b/drivers/nvmem/layouts/fixed-layout.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2026 Bootlin
+ *
+ * Authors: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
+ */
+
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
+
+#include "../internals.h"
+
+static int fixed_layout_add_cells(struct nvmem_layout *layout)
+{
+	struct device_node *np;
+	int ret;
+
+	np = of_nvmem_layout_get_container(layout->nvmem);
+	if (!np)
+		return -ENOENT;
+
+	ret = nvmem_add_cells_from_dt(layout->nvmem, np);
+	of_node_put(np);
+
+	return ret;
+}
+
+static int fixed_layout_probe(struct nvmem_layout *layout)
+{
+	layout->add_cells = fixed_layout_add_cells;
+
+	return nvmem_layout_register(layout);
+}
+
+static void fixed_layout_remove(struct nvmem_layout *layout)
+{
+	nvmem_layout_unregister(layout);
+}
+
+static const struct of_device_id fixed_layout_of_match_table[] = {
+	{ .compatible = "fixed-layout", },
+	{},
+};
+
+static struct nvmem_layout_driver fixed_layout_layout = {
+	.driver = {
+		.name = "fixed-layout",
+		.of_match_table = fixed_layout_of_match_table,
+	},
+	.probe = fixed_layout_probe,
+	.remove = fixed_layout_remove,
+};
+module_nvmem_layout_driver(fixed_layout_layout);
+
+MODULE_AUTHOR("Mathieu Dubois-Briand");
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(of, fixed_layout_of_match_table);
+MODULE_DESCRIPTION("NVMEM fixed-layout driver");