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, 62 insertions, 0 deletions

diff --git a/rust/helpers/task.c b/rust/helpers/task.c
new file mode 100644
index 000000000..c0e1a06ed
--- /dev/null
+++ b/rust/helpers/task.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+#include <linux/sched/task.h>
+
+__rust_helper void rust_helper_might_resched(void)
+{
+	might_resched();
+}
+
+__rust_helper struct task_struct *rust_helper_get_current(void)
+{
+	return current;
+}
+
+__rust_helper void rust_helper_get_task_struct(struct task_struct *t)
+{
+	get_task_struct(t);
+}
+
+__rust_helper void rust_helper_put_task_struct(struct task_struct *t)
+{
+	put_task_struct(t);
+}
+
+__rust_helper kuid_t rust_helper_task_uid(struct task_struct *task)
+{
+	return task_uid(task);
+}
+
+__rust_helper kuid_t rust_helper_task_euid(struct task_struct *task)
+{
+	return task_euid(task);
+}
+
+#ifndef CONFIG_USER_NS
+__rust_helper uid_t rust_helper_from_kuid(struct user_namespace *to, kuid_t uid)
+{
+	return from_kuid(to, uid);
+}
+#endif /* CONFIG_USER_NS */
+
+__rust_helper bool rust_helper_uid_eq(kuid_t left, kuid_t right)
+{
+	return uid_eq(left, right);
+}
+
+__rust_helper kuid_t rust_helper_current_euid(void)
+{
+	return current_euid();
+}
+
+__rust_helper struct user_namespace *rust_helper_current_user_ns(void)
+{
+	return current_user_ns();
+}
+
+__rust_helper pid_t rust_helper_task_tgid_nr_ns(struct task_struct *tsk,
+						struct pid_namespace *ns)
+{
+	return task_tgid_nr_ns(tsk, ns);
+}