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, 106 insertions, 0 deletions

diff --git a/scripts/livepatch/init.c b/scripts/livepatch/init.c
new file mode 100644
index 000000000..f14d8c8fb
--- /dev/null
+++ b/scripts/livepatch/init.c
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Init code for a livepatch kernel module
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/livepatch.h>
+
+static struct klp_patch *patch;
+
+static int __init livepatch_mod_init(void)
+{
+	struct klp_object_ext *obj_exts;
+	size_t obj_exts_sec_size;
+	struct klp_object *objs;
+	unsigned int nr_objs;
+	int ret;
+
+	obj_exts = klp_find_section_by_name(THIS_MODULE, ".init.klp_objects",
+					    &obj_exts_sec_size);
+	nr_objs = obj_exts_sec_size / sizeof(*obj_exts);
+	if (!nr_objs) {
+		pr_err("nothing to patch!\n");
+		ret = -EINVAL;
+		goto err;
+	}
+
+	patch = kzalloc_obj(*patch);
+	if (!patch) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	objs = kzalloc(sizeof(struct klp_object) * (nr_objs + 1),  GFP_KERNEL);
+	if (!objs) {
+		ret = -ENOMEM;
+		goto err_free_patch;
+	}
+
+	for (int i = 0; i < nr_objs; i++) {
+		struct klp_object_ext *obj_ext = obj_exts + i;
+		struct klp_func_ext *funcs_ext = obj_ext->funcs;
+		unsigned int nr_funcs = obj_ext->nr_funcs;
+		struct klp_func *funcs = objs[i].funcs;
+		struct klp_object *obj = objs + i;
+
+		funcs = kzalloc(sizeof(struct klp_func) * (nr_funcs + 1), GFP_KERNEL);
+		if (!funcs) {
+			ret = -ENOMEM;
+			for (int j = 0; j < i; j++)
+				kfree(objs[i].funcs);
+			goto err_free_objs;
+		}
+
+		for (int j = 0; j < nr_funcs; j++) {
+			funcs[j].old_name   = funcs_ext[j].old_name;
+			funcs[j].new_func   = funcs_ext[j].new_func;
+			funcs[j].old_sympos = funcs_ext[j].sympos;
+		}
+
+		obj->name = obj_ext->name;
+		obj->funcs = funcs;
+
+		memcpy(&obj->callbacks, &obj_ext->callbacks, sizeof(struct klp_callbacks));
+	}
+
+	patch->mod = THIS_MODULE;
+	patch->objs = objs;
+
+	/* TODO patch->states */
+
+#ifdef KLP_NO_REPLACE
+	patch->replace = false;
+#else
+	patch->replace = true;
+#endif
+
+	return klp_enable_patch(patch);
+
+err_free_objs:
+	kfree(objs);
+err_free_patch:
+	kfree(patch);
+err:
+	return ret;
+}
+
+static void __exit livepatch_mod_exit(void)
+{
+	struct klp_object *obj;
+
+	klp_for_each_object_static(patch, obj)
+		kfree(obj->funcs);
+
+	kfree(patch->objs);
+	kfree(patch);
+}
+
+module_init(livepatch_mod_init);
+module_exit(livepatch_mod_exit);
+MODULE_LICENSE("GPL");
+MODULE_INFO(livepatch, "Y");
+MODULE_DESCRIPTION("Livepatch module");