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, 13 insertions, 0 deletions

diff --git a/rust/syn/README.md b/rust/syn/README.md
new file mode 100644
index 000000000..d3e3981da
--- /dev/null
+++ b/rust/syn/README.md
@@ -0,0 +1,13 @@
+# `syn`
+
+These source files come from the Rust `syn` crate, version 2.0.106
+(released 2025-08-16), hosted in the <https://github.com/dtolnay/syn>
+repository, licensed under "Apache-2.0 OR MIT" and only modified to add
+the SPDX license identifiers and to remove the `unicode-ident`
+dependency.
+
+For copyright details, please see:
+
+    https://github.com/dtolnay/syn/blob/2.0.106/README.md#license
+    https://github.com/dtolnay/syn/blob/2.0.106/LICENSE-APACHE
+    https://github.com/dtolnay/syn/blob/2.0.106/LICENSE-MIT