[PATCH v2 1/1] stackleak: Register the 'stackleak_cleanup' pass before the '*free_cfg' pass

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[PATCH v2 1/1] stackleak: Register the 'stackleak_cleanup' pass before the '*free_cfg' pass

Alexander Popov
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 <[hidden email]>
Signed-off-by: Alexander Popov <[hidden email]>
---
 scripts/gcc-plugins/stackleak_plugin.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/scripts/gcc-plugins/stackleak_plugin.c b/scripts/gcc-plugins/stackleak_plugin.c
index 2f48da9..dbd3746 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"));
--
2.7.4

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Re: [PATCH v2 1/1] stackleak: Register the 'stackleak_cleanup' pass before the '*free_cfg' pass

Kees Cook-2
On Thu, Dec 6, 2018 at 7:13 AM Alexander Popov <[hidden email]> wrote:

>
> 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 <[hidden email]>
> Signed-off-by: Alexander Popov <[hidden email]>

Thanks! I've applied this to me tree and I'll send a pull request soon.

-Kees

> ---
>  scripts/gcc-plugins/stackleak_plugin.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/scripts/gcc-plugins/stackleak_plugin.c b/scripts/gcc-plugins/stackleak_plugin.c
> index 2f48da9..dbd3746 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"));
> --
> 2.7.4
>


--
Kees Cook