[PATCH 1/1] stackleak: Register the 'stackleak_cleanup' pass before the 'mach' pass

[Kees Cook]

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 'mach' pass, which performs the machine dependent code transformations.
It's the moment when the stack frame size is final and function prologues
and epilogues are already generated.
[1] https://www.openwall.com/lists/kernel-hardening/2018/11/23/2

Thanks, applied!

-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..6f41b32 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 "mach"
+ * pass, which performs the machine dependent code transformations.
+ * It's the moment when the stack frame size is already final and
+ * function prologues and epilogues are generated.
*/
- PASS_INFO(stackleak_cleanup, "reload", 1, PASS_POS_INSERT_AFTER);
+ PASS_INFO(stackleak_cleanup, "mach", 1, PASS_POS_INSERT_BEFORE);
if (!plugin_default_version_check(version, &gcc_version)) {
error(G_("incompatible gcc/plugin versions"));
--
2.7.4

[Kees Cook]

Post by Kees Cook

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 'mach' pass, which performs the machine dependent code transformations.
It's the moment when the stack frame size is final and function prologues
and epilogues are already generated.
[1] https://www.openwall.com/lists/kernel-hardening/2018/11/23/2

Thanks, applied!

Eek, no, this is breaking my build badly:

*** WARNING *** there are active plugins, do not report this as a bug
unless you can reproduce it without enabling any plugins.
Event | Plugins
PLUGIN_START_UNIT | stackleak_plugin
kernel/exit.c: In function ‘release_task’:
kernel/exit.c:228:1: internal compiler error: Segmentation fault
}

Failing with:

gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0

-Kees

Post by Kees Cook
-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..6f41b32 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 "mach"
+ * pass, which performs the machine dependent code transformations.
+ * It's the moment when the stack frame size is already final and
+ * function prologues and epilogues are generated.
*/
- PASS_INFO(stackleak_cleanup, "reload", 1, PASS_POS_INSERT_AFTER);
+ PASS_INFO(stackleak_cleanup, "mach", 1, PASS_POS_INSERT_BEFORE);
if (!plugin_default_version_check(version, &gcc_version)) {
error(G_("incompatible gcc/plugin versions"));
--
2.7.4

--
Kees Cook

[Alexander Popov]

Post by Kees Cook

Post by Kees Cook

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 'mach' pass, which performs the machine dependent code transformations.
It's the moment when the stack frame size is final and function prologues
and epilogues are already generated.
[1] https://www.openwall.com/lists/kernel-hardening/2018/11/23/2

Thanks, applied!

*** WARNING *** there are active plugins, do not report this as a bug
unless you can reproduce it without enabling any plugins.
Event | Plugins
PLUGIN_START_UNIT | stackleak_plugin
kernel/exit.c:228:1: internal compiler error: Segmentation fault
}
gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0

Nice... I don't reproduce it with gcc-7.3 built from source.
I'll investigate this, return with details and we'll decide what to do.

Thanks,
Alexander