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, 30 insertions, 0 deletions

diff --git a/tools/perf/util/rwsem.h b/tools/perf/util/rwsem.h
new file mode 100644
index 000000000..b102d8143
--- /dev/null
+++ b/tools/perf/util/rwsem.h
@@ -0,0 +1,30 @@
+#ifndef _PERF_RWSEM_H
+#define _PERF_RWSEM_H
+
+#include <pthread.h>
+#include "mutex.h"
+
+/*
+ * Mutexes have additional error checking. Enable to use a mutex rather than a
+ * rwlock for debugging.
+ */
+#define RWS_ERRORCHECK 0
+
+struct LOCKABLE rw_semaphore {
+#if RWS_ERRORCHECK
+	struct mutex mtx;
+#else
+	pthread_rwlock_t lock;
+#endif
+};
+
+int init_rwsem(struct rw_semaphore *sem);
+int exit_rwsem(struct rw_semaphore *sem);
+
+int down_read(struct rw_semaphore *sem) SHARED_LOCK_FUNCTION(sem);
+int up_read(struct rw_semaphore *sem) UNLOCK_FUNCTION(sem);
+
+int down_write(struct rw_semaphore *sem) EXCLUSIVE_LOCK_FUNCTION(sem);
+int up_write(struct rw_semaphore *sem) UNLOCK_FUNCTION(sem);
+
+#endif /* _PERF_RWSEM_H */