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, 28 insertions, 0 deletions

diff --git a/rust/helpers/xarray.c b/rust/helpers/xarray.c
new file mode 100644
index 000000000..08979b304
--- /dev/null
+++ b/rust/helpers/xarray.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/xarray.h>
+
+__rust_helper int rust_helper_xa_err(void *entry)
+{
+	return xa_err(entry);
+}
+
+__rust_helper void rust_helper_xa_init_flags(struct xarray *xa, gfp_t flags)
+{
+	return xa_init_flags(xa, flags);
+}
+
+__rust_helper int rust_helper_xa_trylock(struct xarray *xa)
+{
+	return xa_trylock(xa);
+}
+
+__rust_helper void rust_helper_xa_lock(struct xarray *xa)
+{
+	return xa_lock(xa);
+}
+
+__rust_helper void rust_helper_xa_unlock(struct xarray *xa)
+{
+	return xa_unlock(xa);
+}