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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>
This commit is contained in:
Kees Cook 2019-01-23 15:19:29 -08:00
parent 49a57857ae
commit 81a56f6dcd
3 changed files with 73 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
scripts/Makefile.gcc-plugins
View File

@ -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) \

56
scripts/gcc-plugins/Kconfig
View File

@ -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.
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 ported from grsecurity/PaX. More information at:
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"

32
scripts/gcc-plugins/structleak_plugin.c
View File

@ -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"
"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"
(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);