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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ca1ee656d6d852952670b0e63fd19f7499c679a6..5880c993002b32d822c1fddeb85ffb65301515ea 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8627,12 +8627,8 @@ 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 d80cee49e0eb4e39afb0127a4541411334e0d285..8ddf36e5eb42300f0df81bdb34a4bd3f56171c58 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1964,4 +1964,22 @@ static inline void tracer_hardirqs_off(unsigned long a0, unsigned long a1) { }
 
 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 810d78a8d14c76b02efa3dff91b63e52e4c66feb..2905a3dd94c1dba28ebad4282952815f3a38c805 100644 (file)
--- a/kernel/trace/trace_kdb.c
+++ b/kernel/trace/trace_kdb.c
@@ -41,12 +41,8 @@ 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) {