stackleak: Register the 'stackleak_cleanup' pass before the '*free_cfg' pass

Currently the 'stackleak_cleanup' pass deleting a CALL insn is executed
after the 'reload' pass. That allows gcc to do some weird optimization in
function prologues and epilogues, which are generated later [1].

Let's avoid that by registering the 'stackleak_cleanup' pass before
the '*free_cfg' pass. It's the moment when the stack frame size is
already final, function prologues and epilogues are generated, and the
machine-dependent code transformations are not done.

[1] https://www.openwall.com/lists/kernel-hardening/2018/11/23/2

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/scripts/gcc-plugins/stackleak_plugin.c b/scripts/gcc-plugins/stackleak_plugin.c
index 2f48da98b5d4..dbd37460c573 100644
--- a/scripts/gcc-plugins/stackleak_plugin.c
+++ b/scripts/gcc-plugins/stackleak_plugin.c
@@ -363,10 +363,12 @@ __visible int plugin_init(struct plugin_name_args *plugin_info,
                                                 PASS_POS_INSERT_BEFORE);
 
         /*
-         * The stackleak_cleanup pass should be executed after the
-         * "reload" pass, when the stack frame size is final.
+         * The stackleak_cleanup pass should be executed before the "*free_cfg"
+         * pass. It's the moment when the stack frame size is already final,
+         * function prologues and epilogues are generated, and the
+         * machine-dependent code transformations are not done.
          */
-        PASS_INFO(stackleak_cleanup, "reload", 1, PASS_POS_INSERT_AFTER);
+        PASS_INFO(stackleak_cleanup, "*free_cfg", 1, PASS_POS_INSERT_BEFORE);
 
         if (!plugin_default_version_check(version, &gcc_version)) {
                 error(G_("incompatible gcc/plugin versions"));