Re: [kernel-hardening] Merge in PAX_MEMORY_SANITIZE work from grsec to linux-next

Kaiwan N Billimoria
2017-02-24T09:38:24Z

On Tue, 21 Feb 2017 15:26:03 -0800
Kees Cook <keescook@chromium.org> wrote:

> I think mem_sanitize should likely follow the logic used by
> pax_sanitize_slab. i.e CONFIG_MEMORIZE_SANITIZE as suggested above,
> then a mem_sanitize= option for "off" and "full". (i.e.
> CONFIG_MEMORIZE_SANITIZE implies "on")
>
> -Kees
>

Okay. So, while I found that the (pseudo)code you quickly mentioned did not
exactly work out, I have (hopefully) implemented the idea.

A qs: currently, the slub_debug option gets set to 'p' as long as MEMORY_SANITIZE
is enabled, even if the user passes 'slub_debug=-' on the command line. Is this ok?

Pl review the patch below:

diff --git a/init/main.c b/init/main.c
index 63d640e..4397a11 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1027,6 +1027,11 @@ static noinline void __init kernel_init_freeable(void)

do_basic_setup();

+#ifdef CONFIG_MEMORY_SANITIZE
+ pr_debug("[CONFIG_MEMORY_SANITIZE]: page_poisoning_enabled? %s\n",
+ page_poisoning_enabled() ? "yes" : "no");
+#endif
+
/* Open the /dev/console on the rootfs, this should never fail */
if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
pr_err("Warning: unable to open an initial console.\n");
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 3c88b7e..e8aa61d 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -97,3 +97,25 @@ config DEBUG_RODATA_TEST
---help---
This option enables a testcase for the setting rodata read-only.

+config MEMORY_SANITIZE
+ bool "Enable memory sanitization features"
+ select SLUB_DEBUG
+ select PAGE_POISONING
+ select PAGE_POISONING_NO_SANITY
+ ---help---
+ This option enables memory sanitization features. Particularly,
+ when you turn on this option, it auto-enables:
+ - SLUB debug
+ - page poisoning
+ - page poisoning no sanity.
+
+ Implication: turning this option on _will_ implicitly enable:
+ - the SLUB_DEBUG switch to the equivalent of the kernel command-line
+ 'slub_debug=p' ; (where p=SLAB_POISON),
+ - page poisoning, equivalent to passing the kernel command-line option
+ 'page_poison=on'.
+ Of course, kernel command-line options 'page_poison' and 'slub_debug'
+ are still honoured (except that slub-debug will always have the 'p' set).
+
+ If unsure, say N.
+
diff --git a/mm/page_poison.c b/mm/page_poison.c
index 2e647c6..0ca3bc5 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -7,7 +7,8 @@
#include <linux/ratelimit.h>

static bool __page_poisoning_enabled __read_mostly;
-static bool want_page_poisoning __read_mostly;
+static bool want_page_poisoning __read_mostly =
+ IS_ENABLED(CONFIG_MEMORY_SANITIZE);

static int early_page_poison_param(char *buf)
{
@@ -49,6 +50,17 @@ struct page_ext_operations page_poisoning_ops = {
.init = init_page_poisoning,
};

+static int __init memory_sanitize_pagepoison_init(void)
+{
+ */
+ if (IS_ENABLED(CONFIG_MEMORY_SANITIZE) && !want_page_poisoning)
+ __page_poisoning_enabled = false;
+ return 0;
+}
+early_initcall(memory_sanitize_pagepoison_init);
+
static inline void set_page_poison(struct page *page)
{
struct page_ext *page_ext;
diff --git a/mm/slub.c b/mm/slub.c
index 7f4bc70..76abcec 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -450,15 +450,30 @@ static inline void *restore_red_left(struct kmem_cache *s, void *p)
/*
* Debug settings:
*/
-#if defined(CONFIG_SLUB_DEBUG_ON)
-static int slub_debug = DEBUG_DEFAULT_FLAGS;
-#else
static int slub_debug;
-#endif

static char *slub_debug_slabs;
static int disable_higher_order_debug;

+static int __init memory_sanitize_slubdebug_init(void)
+{
+/* With MEMORY_SANITIZE On, slub_debug Must be set to 'p' */
+ if (IS_ENABLED(CONFIG_SLUB_DEBUG_ON) &&
+ IS_ENABLED(CONFIG_MEMORY_SANITIZE)) {
+ slub_debug |= SLAB_POISON;
+ } else if (!IS_ENABLED(CONFIG_SLUB_DEBUG_ON) &&
+ IS_ENABLED(CONFIG_MEMORY_SANITIZE)) {
+ slub_debug = SLAB_POISON;
+ } else if (IS_ENABLED(CONFIG_SLUB_DEBUG_ON) &&
+ !IS_ENABLED(CONFIG_MEMORY_SANITIZE)) {
+ slub_debug = DEBUG_DEFAULT_FLAGS;
+ } else { /* both disabled */
+ slub_debug = 0;
+ }
+ return 0;
+}
+early_initcall(memory_sanitize_slubdebug_init);
+
/*
* slub is about to manipulate internal object metadata. This memory lies
* outside the range of the allocated object, so accessing it would normally
@@ -5755,6 +5770,11 @@ static int __init slab_sysfs_init(void)
struct kmem_cache *s;
int err;

+#ifdef CONFIG_MEMORY_SANITIZE
+ pr_info("[CONFIG_MEMORY_SANITIZE]: slub_debug = P? %s [0x%x]\n",
+ slub_debug & SLAB_POISON ? "yes" : "no", slub_debug);
+#endif
+
mutex_lock(&slab_mutex);

slab_kset = kset_create_and_add("slab", &slab_uevent_ops, kernel_kobj);

Thanks,
Kaiwan.