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Date: Fri, 22 Apr 2016 20:51:08 +0200
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Emese Revfy <re.emese@...il.com>
Cc: "open list:KERNEL BUILD + fi..." <linux-kbuild@...r.kernel.org>, PaX Team <pageexec@...email.hu>, 
	Brad Spengler <spender@...ecurity.net>, kernel-hardening@...ts.openwall.com, 
	Michal Marek <mmarek@...e.com>, Kees Cook <keescook@...omium.org>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>, Fengguang Wu <fengguang.wu@...el.com>, 
	LKML <linux-kernel@...r.kernel.org>, david.brown@...aro.org, 
	yamada.masahiro@...ionext.com, syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH v7 6/6] Add sancov plugin

On Fri, Apr 22, 2016 at 8:27 PM, Emese Revfy <re.emese@...il.com> wrote:
> 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).

+syzkaller mailing list

> Signed-off-by: Emese Revfy <re.emese@...il.com>
> ---
>  Makefile                            |  10 +--
>  arch/Kconfig                        |   9 +++
>  arch/x86/purgatory/Makefile         |   2 +
>  lib/Kconfig.debug                   |   2 +
>  scripts/Makefile.gcc-plugins        |  18 +++++
>  scripts/gcc-plugins/Makefile        |   5 ++
>  scripts/gcc-plugins/sancov_plugin.c | 144 ++++++++++++++++++++++++++++++++++++
>  7 files changed, 181 insertions(+), 9 deletions(-)
>  create mode 100644 scripts/gcc-plugins/sancov_plugin.c
>
> diff --git a/Makefile b/Makefile
> index 22f0e1b..f09f2bf 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -365,7 +365,7 @@ LDFLAGS_MODULE  =
>  CFLAGS_KERNEL  =
>  AFLAGS_KERNEL  =
>  CFLAGS_GCOV    = -fprofile-arcs -ftest-coverage
> -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.
> @@ -685,14 +685,6 @@ 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 e783429..5d856c8 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -380,6 +380,15 @@ 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@...gle.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 4fff4b0..616f7ed 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -708,6 +708,8 @@ 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 282d63a..33ab13e 100644
> --- a/scripts/Makefile.gcc-plugins
> +++ b/scripts/Makefile.gcc-plugins
> @@ -2,8 +2,23 @@ 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
> +        $(error 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/, $(gcc-plugin-y))
>
>    ifeq ($(PLUGINCC),)
> @@ -15,6 +30,9 @@ ifdef CONFIG_GCC_PLUGINS
>          $(error error, 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 31c72bf..79164c1 100644
> --- a/scripts/gcc-plugins/Makefile
> +++ b/scripts/gcc-plugins/Makefile
> @@ -14,6 +14,11 @@ export GCCPLUGINS_DIR HOSTLIBS
>
>  $(HOSTLIBS)-$(CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) := cyc_complexity_plugin.so
>
> +ifeq ($(CFLAGS_KCOV), -fplugin=$(objtree)/scripts/gcc-plugins/sancov_plugin.so)
> +  $(HOSTLIBS)-$(CONFIG_GCC_PLUGIN_SANCOV) += sancov_plugin.so
> +endif
> +
>  always := $($(HOSTLIBS)-y)
>
>  cyc_complexity_plugin-objs := cyc_complexity_plugin.o
> +sancov_plugin-objs := sancov_plugin.o
> 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@...il.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@...gle.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;
> +}
> --
> 2.4.1
>

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