tracing: Silence GCC 9 array bounds warning

commit 0c97bf863efce63d6ab7971dad811601e6171d2f upstream.

Starting with GCC 9, -Warray-bounds detects cases when memset is called
starting on a member of a struct but the size to be cleared ends up
writing over further members.

Such a call happens in the trace code to clear, at once, all members
after and including `seq` on struct trace_iterator:

    In function 'memset',
        inlined from 'ftrace_dump' at kernel/trace/trace.c:8914:3:
    ./include/linux/string.h:344:9: warning: '__builtin_memset' offset
    [8505, 8560] from the object at 'iter' is out of the bounds of
    referenced subobject 'seq' with type 'struct trace_seq' at offset
    4368 [-Warray-bounds]
      344 |  return __builtin_memset(p, c, size);
          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

In order to avoid GCC complaining about it, we compute the address
ourselves by adding the offsetof distance instead of referring
directly to the member.

Since there are two places doing this clear (trace.c and trace_kdb.c),
take the chance to move the workaround into a single place in
the internal header.

Link: http://lkml.kernel.org/r/20190523124535.GA12931@gmail.com
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
[ Removed unnecessary parenthesis around "iter" ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[sw0312.kim: cherry-pick from stable linux-4.4.y commit f7247666a71a for gcc 9 build]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I40614f52191f6ce8ca3c5f8e334867feaf8aac5f

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1a47a64d623f78508cadcc4b3fa9c8147ffd2e23..9514b64a5bdd4eb897d487713635ffe9caa8c17b 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7188,12 +7188,8 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
 
                cnt++;
 
-               /* reset all but tr, trace, and overruns */
-               memset(&iter.seq, 0,
-                      sizeof(struct trace_iterator) -
-                      offsetof(struct trace_iterator, seq));
+               trace_iterator_reset(&iter);
                iter.iter_flags |= TRACE_FILE_LAT_FMT;
-               iter.pos = -1;
 
                if (trace_find_next_entry_inc(&iter) != NULL) {
                        int ret;

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 919d9d07686f5bcaad65699f400748a4b4db8a5e..12a82a7ad5a689f3992d5e71a7542d2c020d194f 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1381,4 +1381,22 @@ static inline void trace_event_enum_update(struct trace_enum_map **map, int len)
 
 extern struct trace_iterator *tracepoint_print_iter;
 
+/*
+ * Reset the state of the trace_iterator so that it can read consumed data.
+ * Normally, the trace_iterator is used for reading the data when it is not
+ * consumed, and must retain state.
+ */
+static __always_inline void trace_iterator_reset(struct trace_iterator *iter)
+{
+       const size_t offset = offsetof(struct trace_iterator, seq);
+
+       /*
+        * Keep gcc from complaining about overwriting more than just one
+        * member in the structure.
+        */
+       memset((char *)iter + offset, 0, sizeof(struct trace_iterator) - offset);
+
+       iter->pos = -1;
+}
+
 #endif /* _LINUX_KERNEL_TRACE_H */

diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
index 57149bce6aad679567a65b95eed2b007e19b4d81..d955526fe73a6b0b29065d628637e0671187c8de 100644 (file)
--- a/kernel/trace/trace_kdb.c
+++ b/kernel/trace/trace_kdb.c
@@ -40,12 +40,8 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
 
        kdb_printf("Dumping ftrace buffer:\n");
 
-       /* reset all but tr, trace, and overruns */
-       memset(&iter.seq, 0,
-                  sizeof(struct trace_iterator) -
-                  offsetof(struct trace_iterator, seq));
+       trace_iterator_reset(&iter);
        iter.iter_flags |= TRACE_FILE_LAT_FMT;
-       iter.pos = -1;
 
        if (cpu_file == RING_BUFFER_ALL_CPUS) {
                for_each_tracing_cpu(cpu) {