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authorKees Cook <keescook@chromium.org>2019-01-23 15:19:29 -0800
committerKees Cook <keescook@chromium.org>2019-03-04 09:29:41 -0800
commit81a56f6dcd20325607d6008f4bb560c96f4c821a (patch)
treec41d189a7cc44326833ecd9fddc98cb063ab66e0
parent49a57857aeea06ca831043acbb0fa5e0f50602fd (diff)
gcc-plugins: structleak: Generalize to all variable types
This adjusts structleak to also work with non-struct types when they are passed by reference, since those variables may leak just like anything else. This is exposed via an improved set of Kconfig options. (This does mean structleak is slightly misnamed now.) Building with CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL should give the kernel complete initialization coverage of all stack variables passed by reference, including padding (see lib/test_stackinit.c). Using CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE to count added initializations under defconfig: ..._BYREF: 5945 added initializations ..._BYREF_ALL: 16606 added initializations There is virtually no change to text+data size (both have less than 0.05% growth): text data bss dec hex filename 19502103 5051456 1917000 26470559 193e89f vmlinux.stock 19513412 5051456 1908808 26473676 193f4cc vmlinux.byref 19516974 5047360 1900616 26464950 193d2b6 vmlinux.byref_all The measured performance difference is in the noise for hackbench and kernel build benchmarks: Stock: 5x hackbench -g 20 -l 1000 Mean: 10.649s Std Dev: 0.339 5x kernel build (4-way parallel) Mean: 261.98s Std Dev: 1.53 CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF: 5x hackbench -g 20 -l 1000 Mean: 10.540s Std Dev: 0.233 5x kernel build (4-way parallel) Mean: 260.52s Std Dev: 1.31 CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL: 5x hackbench -g 20 -l 1000 Mean: 10.320 Std Dev: 0.413 5x kernel build (4-way parallel) Mean: 260.10 Std Dev: 0.86 This does not yet solve missing padding initialization for structures on the stack that are never passed by reference (which should be a tiny minority). Hopefully this will be more easily addressed by upstream compiler fixes after clarifying the C11 padding initialization specification. Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
-rw-r--r--scripts/Makefile.gcc-plugins2
-rw-r--r--scripts/gcc-plugins/Kconfig58
-rw-r--r--scripts/gcc-plugins/structleak_plugin.c36
3 files changed, 74 insertions, 22 deletions
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 35042d96cf5d..5f7df50cfe7a 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -15,6 +15,8 @@ gcc-plugin-$(CONFIG_GCC_PLUGIN_SANCOV) += sancov_plugin.so
gcc-plugin-$(CONFIG_GCC_PLUGIN_STRUCTLEAK) += structleak_plugin.so
gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE) \
+= -fplugin-arg-structleak_plugin-verbose
+gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF) \
+ += -fplugin-arg-structleak_plugin-byref
gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL) \
+= -fplugin-arg-structleak_plugin-byref-all
gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK) \
diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig
index d45f7f36b859..d0cc92e48f6f 100644
--- a/scripts/gcc-plugins/Kconfig
+++ b/scripts/gcc-plugins/Kconfig
@@ -67,27 +67,63 @@ config GCC_PLUGIN_LATENT_ENTROPY
* https://pax.grsecurity.net/
config GCC_PLUGIN_STRUCTLEAK
- bool "Force initialization of variables containing userspace addresses"
+ bool "Zero initialize stack variables"
# Currently STRUCTLEAK inserts initialization out of live scope of
# variables from KASAN point of view. This leads to KASAN false
# positive reports. Prohibit this combination for now.
depends on !KASAN_EXTRA
help
- This plugin zero-initializes any structures containing a
- __user attribute. This can prevent some classes of information
- exposures.
-
- This plugin was ported from grsecurity/PaX. More information at:
+ While the kernel is built with warnings enabled for any missed
+ stack variable initializations, this warning is silenced for
+ anything passed by reference to another function, under the
+ occasionally misguided assumption that the function will do
+ the initialization. As this regularly leads to exploitable
+ flaws, this plugin is available to identify and zero-initialize
+ such variables, depending on the chosen level of coverage.
+
+ This plugin was originally ported from grsecurity/PaX. More
+ information at:
* https://grsecurity.net/
* https://pax.grsecurity.net/
-config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
- bool "Force initialize all struct type variables passed by reference"
+choice
+ prompt "Coverage"
depends on GCC_PLUGIN_STRUCTLEAK
- depends on !COMPILE_TEST
+ default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
help
- Zero initialize any struct type local variable that may be passed by
- reference without having been initialized.
+ This chooses the level of coverage over classes of potentially
+ uninitialized variables. The selected class will be
+ zero-initialized before use.
+
+ config GCC_PLUGIN_STRUCTLEAK_USER
+ bool "structs marked for userspace"
+ help
+ Zero-initialize any structures on the stack containing
+ a __user attribute. This can prevent some classes of
+ uninitialized stack variable exploits and information
+ exposures, like CVE-2013-2141:
+ https://git.kernel.org/linus/b9e146d8eb3b9eca
+
+ config GCC_PLUGIN_STRUCTLEAK_BYREF
+ bool "structs passed by reference"
+ help
+ Zero-initialize any structures on the stack that may
+ be passed by reference and had not already been
+ explicitly initialized. This can prevent most classes
+ of uninitialized stack variable exploits and information
+ exposures, like CVE-2017-1000410:
+ https://git.kernel.org/linus/06e7e776ca4d3654
+
+ config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
+ bool "anything passed by reference"
+ help
+ Zero-initialize any stack variables that may be passed
+ by reference and had not already been explicitly
+ initialized. This is intended to eliminate all classes
+ of uninitialized stack variable exploits and information
+ exposures.
+
+endchoice
config GCC_PLUGIN_STRUCTLEAK_VERBOSE
bool "Report forcefully initialized variables"
diff --git a/scripts/gcc-plugins/structleak_plugin.c b/scripts/gcc-plugins/structleak_plugin.c
index 10292f791e99..e89be8f5c859 100644
--- a/scripts/gcc-plugins/structleak_plugin.c
+++ b/scripts/gcc-plugins/structleak_plugin.c
@@ -16,6 +16,7 @@
* Options:
* -fplugin-arg-structleak_plugin-disable
* -fplugin-arg-structleak_plugin-verbose
+ * -fplugin-arg-structleak_plugin-byref
* -fplugin-arg-structleak_plugin-byref-all
*
* Usage:
@@ -26,7 +27,6 @@
* $ gcc -fplugin=./structleak_plugin.so test.c -O2
*
* TODO: eliminate redundant initializers
- * increase type coverage
*/
#include "gcc-common.h"
@@ -37,13 +37,18 @@
__visible int plugin_is_GPL_compatible;
static struct plugin_info structleak_plugin_info = {
- .version = "201607271510vanilla",
+ .version = "20190125vanilla",
.help = "disable\tdo not activate plugin\n"
- "verbose\tprint all initialized variables\n",
+ "byref\tinit structs passed by reference\n"
+ "byref-all\tinit anything passed by reference\n"
+ "verbose\tprint all initialized variables\n",
};
+#define BYREF_STRUCT 1
+#define BYREF_ALL 2
+
static bool verbose;
-static bool byref_all;
+static int byref;
static tree handle_user_attribute(tree *node, tree name, tree args, int flags, bool *no_add_attrs)
{
@@ -118,6 +123,7 @@ static void initialize(tree var)
gimple_stmt_iterator gsi;
tree initializer;
gimple init_stmt;
+ tree type;
/* this is the original entry bb before the forced split */
bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
@@ -148,11 +154,15 @@ static void initialize(tree var)
if (verbose)
inform(DECL_SOURCE_LOCATION(var),
"%s variable will be forcibly initialized",
- (byref_all && TREE_ADDRESSABLE(var)) ? "byref"
- : "userspace");
+ (byref && TREE_ADDRESSABLE(var)) ? "byref"
+ : "userspace");
/* build the initializer expression */
- initializer = build_constructor(TREE_TYPE(var), NULL);
+ type = TREE_TYPE(var);
+ if (AGGREGATE_TYPE_P(type))
+ initializer = build_constructor(type, NULL);
+ else
+ initializer = fold_convert(type, integer_zero_node);
/* build the initializer stmt */
init_stmt = gimple_build_assign(var, initializer);
@@ -184,13 +194,13 @@ static unsigned int structleak_execute(void)
if (!auto_var_in_fn_p(var, current_function_decl))
continue;
- /* only care about structure types */
- if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE)
+ /* only care about structure types unless byref-all */
+ if (byref != BYREF_ALL && TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE)
continue;
/* if the type is of interest, examine the variable */
if (TYPE_USERSPACE(type) ||
- (byref_all && TREE_ADDRESSABLE(var)))
+ (byref && TREE_ADDRESSABLE(var)))
initialize(var);
}
@@ -232,8 +242,12 @@ __visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gc
verbose = true;
continue;
}
+ if (!strcmp(argv[i].key, "byref")) {
+ byref = BYREF_STRUCT;
+ continue;
+ }
if (!strcmp(argv[i].key, "byref-all")) {
- byref_all = true;
+ byref = BYREF_ALL;
continue;
}
error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);