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, 32 insertions, 0 deletions

diff --git a/arch/mips/generic/vmlinux.its.S b/arch/mips/generic/vmlinux.its.S
new file mode 100644
index 000000000..3e2546765
--- /dev/null
+++ b/arch/mips/generic/vmlinux.its.S
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/dts-v1/;
+
+/ {
+	description = KERNEL_NAME;
+	#address-cells = <ADDR_CELLS>;
+
+	images {
+		kernel {
+			description = KERNEL_NAME;
+			data = /incbin/(VMLINUX_BINARY);
+			type = "kernel";
+			arch = "mips";
+			os = "linux";
+			compression = VMLINUX_COMPRESSION;
+			load = /bits/ ADDR_BITS <VMLINUX_LOAD_ADDRESS>;
+			entry = /bits/ ADDR_BITS <VMLINUX_ENTRY_ADDRESS>;
+			hash {
+				algo = "sha1";
+			};
+		};
+	};
+
+	configurations {
+		default = "conf-default";
+
+		conf-default {
+			description = "Generic Linux kernel";
+			kernel = "kernel";
+		};
+	};
+};