perf machine: Fix segfault for kernel.kptr_restrict=2

Michael reported the segfault when kernel.kptr_restrict=2 is set.

  $ perf record ls
  ...
  perf: Segmentation fault
  Obtained 16 stack frames.
  ./perf(dump_stack+0x2d) [0x5068df]
  ./perf(sighandler_dump_stack+0x2d) [0x5069bf]
  ./perf() [0x43e47b]
  /lib64/libc.so.6(+0x3594f) [0x7f762004794f]
  /lib64/libc.so.6(strlen+0x26) [0x7f762009ef86]
  /lib64/libc.so.6(__strdup+0xd) [0x7f762009ecbd]
  ./perf(maps__set_kallsyms_ref_reloc_sym+0x4d) [0x51590f]
  ./perf(machine__create_kernel_maps+0x136) [0x50a7de]
  ./perf(perf_session__create_kernel_maps+0x2c) [0x510a81]
  ./perf(perf_session__new+0x13d) [0x510e23]
  ./perf() [0x43fd61]
  ./perf(cmd_record+0x704) [0x441823]
  ./perf() [0x4bc1a0]
  ./perf() [0x4bc40d]
  ./perf() [0x4bc55f]
  ./perf(main+0x2d5) [0x4bc939]
  Segmentation fault (core dumped)

The reason is that with kernel.kptr_restrict=2, we don't get
the symbol from machine__get_running_kernel_start, which we
want to use in maps__set_kallsyms_ref_reloc_sym and we crash.

Check the symbol name value before calling
maps__set_kallsyms_ref_reloc_sym() and succeed without ref_reloc_sym
being set. It's safe because we check its existence before we use it.

Reported-by: Michael Petlan <mpetlan@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20170626095153.553-1-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index d7f31cb0a4cbeb41e6c02d58323a8848ff82cfc4..5de2b86b9880c88a7570674688cfaba50744b5ed 100644 (file)
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1209,10 +1209,12 @@ int machine__create_kernel_maps(struct machine *machine)
         */
        map_groups__fixup_end(&machine->kmaps);
 
-       if (machine__get_running_kernel_start(machine, &name, &addr)) {
-       } else if (maps__set_kallsyms_ref_reloc_sym(machine->vmlinux_maps, name, addr)) {
-               machine__destroy_kernel_maps(machine);
-               return -1;
+       if (!machine__get_running_kernel_start(machine, &name, &addr)) {
+               if (name &&
+                   maps__set_kallsyms_ref_reloc_sym(machine->vmlinux_maps, name, addr)) {
+                       machine__destroy_kernel_maps(machine);
+                       return -1;
+               }
        }
 
        return 0;