[PATCH v9 4/4] Add sancov plugin

Emese Revfy
2016-05-23T22:04:37Z

The sancov gcc plugin inserts a __sanitizer_cov_trace_pc() call
at the start of basic blocks.

This plugin is a helper plugin for the kcov feature. It supports
all gcc versions with plugin support (from gcc-4.5 on).
It is based on the gcc commit "Add fuzzing coverage support" by Dmitry Vyukov
(https://gcc.gnu.org/viewcvs/gcc?limit_changes=0&view=revision&revision=231296).

Signed-off-by: Emese Revfy <re.emese@gmail.com>
---
Makefile | 10 +--
arch/Kconfig | 9 +++
arch/x86/purgatory/Makefile | 2 +
lib/Kconfig.debug | 2 +
scripts/Makefile.gcc-plugins | 21 +++++-
scripts/gcc-plugins/Makefile | 6 ++
scripts/gcc-plugins/sancov_plugin.c | 144 ++++++++++++++++++++++++++++++++++++
7 files changed, 184 insertions(+), 10 deletions(-)
create mode 100644 scripts/gcc-plugins/sancov_plugin.c

diff --git a/Makefile b/Makefile
index ebe6c3c..b4f8f0a 100644
--- a/Makefile
+++ b/Makefile
@@ -369,7 +369,7 @@ LDFLAGS_MODULE =
CFLAGS_KERNEL =
AFLAGS_KERNEL =
CFLAGS_GCOV = -fprofile-arcs -ftest-coverage -fno-tree-loop-im -Wno-maybe-uninitialized
-CFLAGS_KCOV = -fsanitize-coverage=trace-pc
+CFLAGS_KCOV := $(call cc-option,-fsanitize-coverage=trace-pc,)

# Use USERINCLUDE when you must reference the UAPI directories only.
@@ -691,14 +691,6 @@ endif
endif
KBUILD_CFLAGS += $(stackp-flag)

-ifdef CONFIG_KCOV
- ifeq ($(call cc-option, $(CFLAGS_KCOV)),)
- $(warning Cannot use CONFIG_KCOV: \
- -fsanitize-coverage=trace-pc is not supported by compiler)
- CFLAGS_KCOV =
- endif
-endif
-
ifeq ($(cc-name),clang)
KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
KBUILD_CPPFLAGS += $(call cc-option,-Wno-unknown-warning-option,)
diff --git a/arch/Kconfig b/arch/Kconfig
index 74f0d63..5feadad 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -384,6 +384,15 @@ config GCC_PLUGIN_CYC_COMPLEXITY
N = the number of nodes
P = the number of connected components (exit nodes).

+config GCC_PLUGIN_SANCOV
+ bool
+ depends on GCC_PLUGINS
+ help
+ This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
+ basic blocks. It supports all gcc versions with plugin support (from
+ gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
+ by Dmitry Vyukov <dvyukov@google.com>.
+
config HAVE_CC_STACKPROTECTOR
bool
help
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 12734a9..ac58c16 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -8,6 +8,8 @@ PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
targets += purgatory.ro

+KCOV_INSTRUMENT := n
+
# Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
# in turn leaves some undefined symbols like __fentry__ in purgatory and not
# sure how to relocate those. Like kexec-tools, use custom flags.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 09cdb1f..7c7980d 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -712,6 +712,8 @@ config KCOV
bool "Code coverage for fuzzing"
depends on ARCH_HAS_KCOV
select DEBUG_FS
+ select GCC_PLUGINS
+ select GCC_PLUGIN_SANCOV
help
KCOV exposes kernel code coverage information in a form suitable
for coverage-guided fuzzing (randomized testing).
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index b4a189c..ed37e9b 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -2,10 +2,26 @@ ifdef CONFIG_GCC_PLUGINS
__PLUGINCC := $(call cc-ifversion, -ge, 0408, $(HOSTCXX), $(HOSTCC))
PLUGINCC := $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-plugin.sh "$(__PLUGINCC)" "$(HOSTCXX)" "$(CC)")

+ SANCOV_PLUGIN := -fplugin=$(objtree)/scripts/gcc-plugins/sancov_plugin.so
+
gcc-plugin-$(CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) += cyc_complexity_plugin.so
+
+ ifdef CONFIG_GCC_PLUGIN_SANCOV
+ ifeq ($(CFLAGS_KCOV),)
+ # It is needed because of the gcc-plugin.sh and gcc version checks.
+ gcc-plugin-$(CONFIG_GCC_PLUGIN_SANCOV) += sancov_plugin.so
+
+ ifneq ($(PLUGINCC),)
+ CFLAGS_KCOV := $(SANCOV_PLUGIN)
+ else
+ $(warning warning: cannot use CONFIG_KCOV: -fsanitize-coverage=trace-pc is not supported by compiler)
+ endif
+ endif
+ endif
+
GCC_PLUGINS_CFLAGS := $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y))

- export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN
+ export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN SANCOV_PLUGIN

ifeq ($(PLUGINCC),)
ifneq ($(GCC_PLUGINS_CFLAGS),)
@@ -16,6 +32,9 @@ ifdef CONFIG_GCC_PLUGINS
$(warning warning: your gcc version does not support plugins, you should upgrade it to gcc 4.5 at least)
endif
endif
+ else
+ # SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication.
+ GCC_PLUGINS_CFLAGS := $(filter-out $(SANCOV_PLUGIN), $(GCC_PLUGINS_CFLAGS))
endif

KBUILD_CFLAGS += $(GCC_PLUGINS_CFLAGS)
diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index c60ba4b..88c8ec4 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -14,8 +14,14 @@ endif

export GCCPLUGINS_DIR HOSTLIBS

+ifneq ($(CFLAGS_KCOV), $(SANCOV_PLUGIN))
+ GCC_PLUGIN := $(filter-out $(SANCOV_PLUGIN), $(GCC_PLUGIN))
+endif
+
$(HOSTLIBS)-y := $(GCC_PLUGIN)
always := $($(HOSTLIBS)-y)

cyc_complexity_plugin-objs := cyc_complexity_plugin.o
+sancov_plugin-objs := sancov_plugin.o
+
clean-files += *.so
diff --git a/scripts/gcc-plugins/sancov_plugin.c b/scripts/gcc-plugins/sancov_plugin.c
new file mode 100644
index 0000000..aedd611
--- /dev/null
+++ b/scripts/gcc-plugins/sancov_plugin.c
@@ -0,0 +1,144 @@
+/*
+ * Copyright 2011-2016 by Emese Revfy <re.emese@gmail.com>
+ * Licensed under the GPL v2, or (at your option) v3
+ *
+ * Homepage:
+ * https://github.com/ephox-gcc-plugins/sancov
+ *
+ * This plugin inserts a __sanitizer_cov_trace_pc() call at the start of basic blocks.
+ * It supports all gcc versions with plugin support (from gcc-4.5 on).
+ * It is based on the commit "Add fuzzing coverage support" by Dmitry Vyukov <dvyukov@google.com>.
+ *
+ * You can read about it more here:
+ * https://gcc.gnu.org/viewcvs/gcc?limit_changes=0&view=revision&revision=231296
+ * http://lwn.net/Articles/674854/
+ * https://github.com/google/syzkaller
+ * https://lwn.net/Articles/677764/
+ *
+ * Usage:
+ * make run
+ */
+
+#include "gcc-common.h"
+
+int plugin_is_GPL_compatible;
+
+tree sancov_fndecl;
+
+static struct plugin_info sancov_plugin_info = {
+ .version = "20160402",
+ .help = "sancov plugin\n",
+};
+
+static unsigned int sancov_execute(void)
+{
+ basic_block bb;
+
+ /* Remove this line when this plugin and kcov will be in the kernel.
+ if (!strcmp(DECL_NAME_POINTER(current_function_decl), DECL_NAME_POINTER(sancov_fndecl)))
+ return 0;
+ */
+
+ FOR_EACH_BB_FN(bb, cfun) {
+ const_gimple stmt;
+ gcall *gcall;
+ gimple_stmt_iterator gsi = gsi_after_labels(bb);
+
+ if (gsi_end_p(gsi))
+ continue;
+
+ stmt = gsi_stmt(gsi);
+ gcall = as_a_gcall(gimple_build_call(sancov_fndecl, 0));
+ gimple_set_location(gcall, gimple_location(stmt));
+ gsi_insert_before(&gsi, gcall, GSI_SAME_STMT);
+ }
+ return 0;
+}
+
+#define PASS_NAME sancov
+
+#define NO_GATE
+#define TODO_FLAGS_FINISH TODO_dump_func | TODO_verify_stmts | TODO_update_ssa_no_phi | TODO_verify_flow
+
+#include "gcc-generate-gimple-pass.h"
+
+static void sancov_start_unit(void __unused *gcc_data, void __unused *user_data)
+{
+ tree leaf_attr, nothrow_attr;
+ tree BT_FN_VOID = build_function_type_list(void_type_node, NULL_TREE);
+
+ sancov_fndecl = build_fn_decl("__sanitizer_cov_trace_pc", BT_FN_VOID);
+
+ DECL_ASSEMBLER_NAME(sancov_fndecl);
+ TREE_PUBLIC(sancov_fndecl) = 1;
+ DECL_EXTERNAL(sancov_fndecl) = 1;
+ DECL_ARTIFICIAL(sancov_fndecl) = 1;
+ DECL_PRESERVE_P(sancov_fndecl) = 1;
+ DECL_UNINLINABLE(sancov_fndecl) = 1;
+ TREE_USED(sancov_fndecl) = 1;
+
+ nothrow_attr = tree_cons(get_identifier("nothrow"), NULL, NULL);
+ decl_attributes(&sancov_fndecl, nothrow_attr, 0);
+ gcc_assert(TREE_NOTHROW(sancov_fndecl));
+#if BUILDING_GCC_VERSION > 4005
+ leaf_attr = tree_cons(get_identifier("leaf"), NULL, NULL);
+ decl_attributes(&sancov_fndecl, leaf_attr, 0);
+#endif
+}
+
+int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
+{
+ int i;
+ struct register_pass_info sancov_plugin_pass_info;
+ const char * const plugin_name = plugin_info->base_name;
+ const int argc = plugin_info->argc;
+ const struct plugin_argument * const argv = plugin_info->argv;
+ bool enable = true;
+
+ static const struct ggc_root_tab gt_ggc_r_gt_sancov[] = {
+ {
+ .base = &sancov_fndecl,
+ .nelt = 1,
+ .stride = sizeof(sancov_fndecl),
+ .cb = &gt_ggc_mx_tree_node,
+ .pchw = &gt_pch_nx_tree_node
+ },
+ LAST_GGC_ROOT_TAB
+ };
+
+ /* BBs can be split afterwards?? */
+ sancov_plugin_pass_info.pass = make_sancov_pass();
+#if BUILDING_GCC_VERSION >= 4009
+ sancov_plugin_pass_info.reference_pass_name = "asan";
+#else
+ sancov_plugin_pass_info.reference_pass_name = "nrv";
+#endif
+ sancov_plugin_pass_info.ref_pass_instance_number = 0;
+ sancov_plugin_pass_info.pos_op = PASS_POS_INSERT_BEFORE;
+
+ if (!plugin_default_version_check(version, &gcc_version)) {
+ error(G_("incompatible gcc/plugin versions"));
+ return 1;
+ }
+
+ for (i = 0; i < argc; ++i) {
+ if (!strcmp(argv[i].key, "no-sancov")) {
+ enable = false;
+ continue;
+ }
+ error(G_("unkown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
+ }
+
+ register_callback(plugin_name, PLUGIN_INFO, NULL, &sancov_plugin_info);
+
+ if (!enable)
+ return 0;
+
+#if BUILDING_GCC_VERSION < 6000
+ register_callback(plugin_name, PLUGIN_START_UNIT, &sancov_start_unit, NULL);
+ register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS, NULL, (void *)&gt_ggc_r_gt_sancov);
+ register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &sancov_plugin_pass_info);
+#endif
+
+ return 0;
+}
--
2.8.1