Commit 50bbae7d authored by Miguel Ojeda's avatar Miguel Ojeda Committed by Greg Kroah-Hartman

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.comSigned-off-by: default avatarMiguel Ojeda <miguel.ojeda.sandonis@gmail.com>
[ Removed unnecessary parenthesis around "iter" ]
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a5758c53
......@@ -8249,12 +8249,8 @@ 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;
......
......@@ -1871,4 +1871,22 @@ static inline int tracing_alloc_snapshot_instance(struct trace_array *tr)
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 */
......@@ -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) {
......
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