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, 27 insertions, 0 deletions

diff --git a/fs/proc/version.c b/fs/proc/version.c
new file mode 100644
index 000000000..02e3c3cd4
--- /dev/null
+++ b/fs/proc/version.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/utsname.h>
+#include "internal.h"
+
+static int version_proc_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, linux_proc_banner,
+		utsname()->sysname,
+		utsname()->release,
+		utsname()->version);
+	return 0;
+}
+
+static int __init proc_version_init(void)
+{
+	struct proc_dir_entry *pde;
+
+	pde = proc_create_single("version", 0, NULL, version_proc_show);
+	pde_make_permanent(pde);
+	return 0;
+}
+fs_initcall(proc_version_init);