whiterose

linux unikernel
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commit 2bb995405fe52dd893db57456556e8dc4fce35a7
parent a39f009acefd85d3e36bcae828a4e67c9dce9684
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat,  9 Mar 2019 09:06:15 -0800

Merge tag 'gcc-plugins-v5.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull gcc-plugins updates from Kees Cook:
 "This adds additional type coverage to the existing structleak plugin
  and adds a large set of selftests to help evaluate stack variable
  zero-initialization coverage.

  That can be used to test whatever instrumentation might be performing
  zero-initialization: either with the structleak plugin or with Clang's
  coming "-ftrivial-auto-var-init=zero" option.

  Summary:

   - Add scalar and array initialization coverage

   - Refactor Kconfig to make options more clear

   - Add self-test module for testing automatic initialization"

* tag 'gcc-plugins-v5.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  lib: Introduce test_stackinit module
  gcc-plugins: structleak: Generalize to all variable types

Diffstat:
Mlib/Kconfig.debug | 10++++++++++
Mlib/Makefile | 1+
Alib/test_stackinit.c | 378+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Mscripts/Makefile.gcc-plugins | 2++
Mscripts/gcc-plugins/Kconfig | 58+++++++++++++++++++++++++++++++++++++++++++++++-----------
Mscripts/gcc-plugins/structleak_plugin.c | 36+++++++++++++++++++++++++-----------
6 files changed, 463 insertions(+), 22 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug @@ -2016,6 +2016,16 @@ config TEST_OBJAGG (or module load). +config TEST_STACKINIT + tristate "Test level of stack variable initialization" + help + Test if the kernel is zero-initializing stack variables and + padding. Coverage is controlled by compiler flags, + CONFIG_GCC_PLUGIN_STRUCTLEAK, CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF, + or CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL. + + If unsure, say N. + endif # RUNTIME_TESTING_MENU config MEMTEST diff --git a/lib/Makefile b/lib/Makefile @@ -77,6 +77,7 @@ obj-$(CONFIG_TEST_KMOD) += test_kmod.o obj-$(CONFIG_TEST_DEBUG_VIRTUAL) += test_debug_virtual.o obj-$(CONFIG_TEST_MEMCAT_P) += test_memcat_p.o obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o +obj-$(CONFIG_TEST_STACKINIT) += test_stackinit.o obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/ diff --git a/lib/test_stackinit.c b/lib/test_stackinit.c @@ -0,0 +1,378 @@ +// SPDX-Licenses: GPLv2 +/* + * Test cases for compiler-based stack variable zeroing via future + * compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*. + */ +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/string.h> + +/* Exfiltration buffer. */ +#define MAX_VAR_SIZE 128 +static char check_buf[MAX_VAR_SIZE]; + +/* Character array to trigger stack protector in all functions. */ +#define VAR_BUFFER 32 + +/* Volatile mask to convince compiler to copy memory with 0xff. */ +static volatile u8 forced_mask = 0xff; + +/* Location and size tracking to validate fill and test are colocated. */ +static void *fill_start, *target_start; +static size_t fill_size, target_size; + +static bool range_contains(char *haystack_start, size_t haystack_size, + char *needle_start, size_t needle_size) +{ + if (needle_start >= haystack_start && + needle_start + needle_size <= haystack_start + haystack_size) + return true; + return false; +} + +#define DO_NOTHING_TYPE_SCALAR(var_type) var_type +#define DO_NOTHING_TYPE_STRING(var_type) void +#define DO_NOTHING_TYPE_STRUCT(var_type) void + +#define DO_NOTHING_RETURN_SCALAR(ptr) *(ptr) +#define DO_NOTHING_RETURN_STRING(ptr) /**/ +#define DO_NOTHING_RETURN_STRUCT(ptr) /**/ + +#define DO_NOTHING_CALL_SCALAR(var, name) \ + (var) = do_nothing_ ## name(&(var)) +#define DO_NOTHING_CALL_STRING(var, name) \ + do_nothing_ ## name(var) +#define DO_NOTHING_CALL_STRUCT(var, name) \ + do_nothing_ ## name(&(var)) + +#define FETCH_ARG_SCALAR(var) &var +#define FETCH_ARG_STRING(var) var +#define FETCH_ARG_STRUCT(var) &var + +#define FILL_SIZE_STRING 16 + +#define INIT_CLONE_SCALAR /**/ +#define INIT_CLONE_STRING [FILL_SIZE_STRING] +#define INIT_CLONE_STRUCT /**/ + +#define INIT_SCALAR_none /**/ +#define INIT_SCALAR_zero = 0 + +#define INIT_STRING_none [FILL_SIZE_STRING] /**/ +#define INIT_STRING_zero [FILL_SIZE_STRING] = { } + +#define INIT_STRUCT_none /**/ +#define INIT_STRUCT_zero = { } +#define INIT_STRUCT_static_partial = { .two = 0, } +#define INIT_STRUCT_static_all = { .one = arg->one, \ + .two = arg->two, \ + .three = arg->three, \ + .four = arg->four, \ + } +#define INIT_STRUCT_dynamic_partial = { .two = arg->two, } +#define INIT_STRUCT_dynamic_all = { .one = arg->one, \ + .two = arg->two, \ + .three = arg->three, \ + .four = arg->four, \ + } +#define INIT_STRUCT_runtime_partial ; \ + var.two = 0 +#define INIT_STRUCT_runtime_all ; \ + var.one = 0; \ + var.two = 0; \ + var.three = 0; \ + memset(&var.four, 0, \ + sizeof(var.four)) + +/* + * @name: unique string name for the test + * @var_type: type to be tested for zeroing initialization + * @which: is this a SCALAR, STRING, or STRUCT type? + * @init_level: what kind of initialization is performed + */ +#define DEFINE_TEST_DRIVER(name, var_type, which) \ +/* Returns 0 on success, 1 on failure. */ \ +static noinline __init int test_ ## name (void) \ +{ \ + var_type zero INIT_CLONE_ ## which; \ + int ignored; \ + u8 sum = 0, i; \ + \ + /* Notice when a new test is larger than expected. */ \ + BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE); \ + \ + /* Fill clone type with zero for per-field init. */ \ + memset(&zero, 0x00, sizeof(zero)); \ + /* Fill stack with 0xFF. */ \ + ignored = leaf_ ##name((unsigned long)&ignored, 1, \ + FETCH_ARG_ ## which(zero)); \ + /* Clear entire check buffer for later bit tests. */ \ + memset(check_buf, 0x00, sizeof(check_buf)); \ + /* Extract stack-defined variable contents. */ \ + ignored = leaf_ ##name((unsigned long)&ignored, 0, \ + FETCH_ARG_ ## which(zero)); \ + \ + /* Validate that compiler lined up fill and target. */ \ + if (!range_contains(fill_start, fill_size, \ + target_start, target_size)) { \ + pr_err(#name ": stack fill missed target!?\n"); \ + pr_err(#name ": fill %zu wide\n", fill_size); \ + pr_err(#name ": target offset by %d\n", \ + (int)((ssize_t)(uintptr_t)fill_start - \ + (ssize_t)(uintptr_t)target_start)); \ + return 1; \ + } \ + \ + /* Look for any set bits in the check region. */ \ + for (i = 0; i < sizeof(check_buf); i++) \ + sum += (check_buf[i] != 0); \ + \ + if (sum == 0) \ + pr_info(#name " ok\n"); \ + else \ + pr_warn(#name " FAIL (uninit bytes: %d)\n", \ + sum); \ + \ + return (sum != 0); \ +} +#define DEFINE_TEST(name, var_type, which, init_level) \ +/* no-op to force compiler into ignoring "uninitialized" vars */\ +static noinline __init DO_NOTHING_TYPE_ ## which(var_type) \ +do_nothing_ ## name(var_type *ptr) \ +{ \ + /* Will always be true, but compiler doesn't know. */ \ + if ((unsigned long)ptr > 0x2) \ + return DO_NOTHING_RETURN_ ## which(ptr); \ + else \ + return DO_NOTHING_RETURN_ ## which(ptr + 1); \ +} \ +static noinline __init int leaf_ ## name(unsigned long sp, \ + bool fill, \ + var_type *arg) \ +{ \ + char buf[VAR_BUFFER]; \ + var_type var INIT_ ## which ## _ ## init_level; \ + \ + target_start = &var; \ + target_size = sizeof(var); \ + /* \ + * Keep this buffer around to make sure we've got a \ + * stack frame of SOME kind... \ + */ \ + memset(buf, (char)(sp && 0xff), sizeof(buf)); \ + /* Fill variable with 0xFF. */ \ + if (fill) { \ + fill_start = &var; \ + fill_size = sizeof(var); \ + memset(fill_start, \ + (char)((sp && 0xff) | forced_mask), \ + fill_size); \ + } \ + \ + /* Silence "never initialized" warnings. */ \ + DO_NOTHING_CALL_ ## which(var, name); \ + \ + /* Exfiltrate "var". */ \ + memcpy(check_buf, target_start, target_size); \ + \ + return (int)buf[0] | (int)buf[sizeof(buf) - 1]; \ +} \ +DEFINE_TEST_DRIVER(name, var_type, which) + +/* Structure with no padding. */ +struct test_packed { + unsigned long one; + unsigned long two; + unsigned long three; + unsigned long four; +}; + +/* Simple structure with padding likely to be covered by compiler. */ +struct test_small_hole { + size_t one; + char two; + /* 3 byte padding hole here. */ + int three; + unsigned long four; +}; + +/* Try to trigger unhandled padding in a structure. */ +struct test_aligned { + u32 internal1; + u64 internal2; +} __aligned(64); + +struct test_big_hole { + u8 one; + u8 two; + u8 three; + /* 61 byte padding hole here. */ + struct test_aligned four; +} __aligned(64); + +struct test_trailing_hole { + char *one; + char *two; + char *three; + char four; + /* "sizeof(unsigned long) - 1" byte padding hole here. */ +}; + +/* Test if STRUCTLEAK is clearing structs with __user fields. */ +struct test_user { + u8 one; + unsigned long two; + char __user *three; + unsigned long four; +}; + +#define DEFINE_SCALAR_TEST(name, init) \ + DEFINE_TEST(name ## _ ## init, name, SCALAR, init) + +#define DEFINE_SCALAR_TESTS(init) \ + DEFINE_SCALAR_TEST(u8, init); \ + DEFINE_SCALAR_TEST(u16, init); \ + DEFINE_SCALAR_TEST(u32, init); \ + DEFINE_SCALAR_TEST(u64, init); \ + DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init) + +#define DEFINE_STRUCT_TEST(name, init) \ + DEFINE_TEST(name ## _ ## init, \ + struct test_ ## name, STRUCT, init) + +#define DEFINE_STRUCT_TESTS(init) \ + DEFINE_STRUCT_TEST(small_hole, init); \ + DEFINE_STRUCT_TEST(big_hole, init); \ + DEFINE_STRUCT_TEST(trailing_hole, init); \ + DEFINE_STRUCT_TEST(packed, init) + +/* These should be fully initialized all the time! */ +DEFINE_SCALAR_TESTS(zero); +DEFINE_STRUCT_TESTS(zero); +/* Static initialization: padding may be left uninitialized. */ +DEFINE_STRUCT_TESTS(static_partial); +DEFINE_STRUCT_TESTS(static_all); +/* Dynamic initialization: padding may be left uninitialized. */ +DEFINE_STRUCT_TESTS(dynamic_partial); +DEFINE_STRUCT_TESTS(dynamic_all); +/* Runtime initialization: padding may be left uninitialized. */ +DEFINE_STRUCT_TESTS(runtime_partial); +DEFINE_STRUCT_TESTS(runtime_all); +/* No initialization without compiler instrumentation. */ +DEFINE_SCALAR_TESTS(none); +DEFINE_STRUCT_TESTS(none); +DEFINE_TEST(user, struct test_user, STRUCT, none); + +/* + * Check two uses through a variable declaration outside either path, + * which was noticed as a special case in porting earlier stack init + * compiler logic. + */ +static int noinline __leaf_switch_none(int path, bool fill) +{ + switch (path) { + uint64_t var; + + case 1: + target_start = &var; + target_size = sizeof(var); + if (fill) { + fill_start = &var; + fill_size = sizeof(var); + + memset(fill_start, forced_mask | 0x55, fill_size); + } + memcpy(check_buf, target_start, target_size); + break; + case 2: + target_start = &var; + target_size = sizeof(var); + if (fill) { + fill_start = &var; + fill_size = sizeof(var); + + memset(fill_start, forced_mask | 0xaa, fill_size); + } + memcpy(check_buf, target_start, target_size); + break; + default: + var = 5; + return var & forced_mask; + } + return 0; +} + +static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill, + uint64_t *arg) +{ + return __leaf_switch_none(1, fill); +} + +static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill, + uint64_t *arg) +{ + return __leaf_switch_none(2, fill); +} + +DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR); +DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR); + +static int __init test_stackinit_init(void) +{ + unsigned int failures = 0; + +#define test_scalars(init) do { \ + failures += test_u8_ ## init (); \ + failures += test_u16_ ## init (); \ + failures += test_u32_ ## init (); \ + failures += test_u64_ ## init (); \ + failures += test_char_array_ ## init (); \ + } while (0) + +#define test_structs(init) do { \ + failures += test_small_hole_ ## init (); \ + failures += test_big_hole_ ## init (); \ + failures += test_trailing_hole_ ## init (); \ + failures += test_packed_ ## init (); \ + } while (0) + + /* These are explicitly initialized and should always pass. */ + test_scalars(zero); + test_structs(zero); + /* Padding here appears to be accidentally always initialized? */ + test_structs(dynamic_partial); + /* Padding initialization depends on compiler behaviors. */ + test_structs(static_partial); + test_structs(static_all); + test_structs(dynamic_all); + test_structs(runtime_partial); + test_structs(runtime_all); + + /* STRUCTLEAK_BYREF_ALL should cover everything from here down. */ + test_scalars(none); + failures += test_switch_1_none(); + failures += test_switch_2_none(); + + /* STRUCTLEAK_BYREF should cover from here down. */ + test_structs(none); + + /* STRUCTLEAK will only cover this. */ + failures += test_user(); + + if (failures == 0) + pr_info("all tests passed!\n"); + else + pr_err("failures: %u\n", failures); + + return failures ? -EINVAL : 0; +} +module_init(test_stackinit_init); + +static void __exit test_stackinit_exit(void) +{ } +module_exit(test_stackinit_exit); + +MODULE_LICENSE("GPL"); diff --git 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 @@ -67,23 +67,59 @@ 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" 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 @@ -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);