linux-kernel - [PATCH v2 1/1] stackleak: Register the 'stackleak_cleanup' pass before the '*free

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Message-Id: <1544109187-13805-1-git-send-email-alex.popov@linux.com>
Date:   Thu,  6 Dec 2018 18:13:07 +0300
From:   Alexander Popov <alex.popov@...ux.com>
To:     kernel-hardening@...ts.openwall.com,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Richard Sandiford <richard.sandiford@....com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Alexander Monakov <amonakov@...ras.ru>,
        Tycho Andersen <tycho@...ho.ws>,
        Laura Abbott <labbott@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Emese Revfy <re.emese@...il.com>,
        Thomas Garnier <thgarnie@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Will Deacon <will.deacon@....com>,
        Alexei Starovoitov <ast@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        H Peter Anvin <hpa@...or.com>,
        David S Miller <davem@...emloft.net>,
        linux-arm-kernel@...ts.infradead.org, gcc@....gnu.org,
        alex.popov@...ux.com, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/1] 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@...el.com>
Signed-off-by: Alexander Popov <alex.popov@...ux.com>
---
 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