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

Kaiwan N Billimoria
2017-02-09T03:37:14Z

Hi Kees,

> I think CONFIG_MEMORY_SANITIZE would enable:
>
> CONFIG_SLUB_DEBUG=y
> CONFIG_PAGE_POISONING=y
> CONFIG_PAGE_POISONING_NO_SANITY=y
>
> but it would _also_ need to set these kernel command-line variables as
> if they had been set:
>
> page_poison=1
> slub_debug=P
>
> No, the first step would be for the config to only provide the above
> changes.

Have made a first cut (below). Pl take a look and let me know if okay
and how I should proceed.

Note-
- the printks' are just for checking that options are enabled as required
(will get rid of them later)
- this is on linux-next (x86_64)
- dmesg filtered output when booted with this kernel (no page_posion or slub_debug
cmdline options passed):

$ dmesg |grep "MEMORY_SANITIZE"
kern :info : [ +0.000387] [CONFIG_MEMORY_SANITIZE]: slub_debug = P? yes [0x800]
kern :debug : [ +0.000000] [CONFIG_MEMORY_SANITIZE]: page_poisoning_enabled? yes
$

===
diff --git a/init/main.c b/init/main.c
index ef47035..ba44574 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1028,6 +1028,11 @@ 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 3e5eada..8eed6ca 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -97,3 +97,11 @@ 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 if HIBERNATION
+ ---help---
+ This option enables ...
+
diff --git a/mm/page_poison.c b/mm/page_poison.c
index 2e647c6..b45bc0a 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -49,6 +49,19 @@ struct page_ext_operations page_poisoning_ops = {
.init = init_page_poisoning,
};

+#ifdef CONFIG_MEMORY_SANITIZE
+static int __init memory_sanitize_init(void)
+{
+ /* With 'memory sanitize' On, page poisoning Must be turned on */
+ if (IS_ENABLED(CONFIG_MEMORY_SANITIZE)) {
+ want_page_poisoning = true;
+ __page_poisoning_enabled = true;
+ }
+ return 0;
+}
+early_initcall(memory_sanitize_init);
+#endif
+
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 d24e1ce..ed26b10 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -449,10 +449,15 @@ static inline void *restore_red_left(struct kmem_cache *s, void *p)
* Debug settings:
*/
#if defined(CONFIG_SLUB_DEBUG_ON)
+#if defined(CONFIG_MEMORY_SANITIZE)
+/* With 'memory sanitize' On, slub_debug should be 'P' */
+static int slub_debug = SLAB_POISON;
+#else
static int slub_debug = DEBUG_DEFAULT_FLAGS;
+#endif /* CONFIG_MEMORY_SANITIZE */
#else
static int slub_debug;
-#endif
+#endif /* CONFIG_SLUB_DEBUG_ON */

static char *slub_debug_slabs;
static int disable_higher_order_debug;
@@ -5675,6 +5680,11 @@ 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);
===

Regards,
Kaiwan.

> Then, we'd want to add the poison value defaults as you mention:
>
> > -Would include the 'new' poison / sanitize values of 0xfe and 0xff
> > for slab (64 and 32-bit resp), etc etc.
>
> And then finally add the exceptions for the "frequently freed" slub
> caches, as identified by PaX already. This would need the flag
> defined, the poisoning logic adjusted to check the flag, and for the
> new kernel command-line options for changing the whether or not the
> flag is respected (like PaX's "pax_sanitize_slab").
>
> > Even if this is (somewhat) correct, my thinking is - correct me I'm
> > totally wrong here - that the whole purpose of the exercise is to
> > improve _security_; hence, tying this code into the "debug
> > features" of the kernel isn't really what we want, yes?
>
> In the discussions Laura had with the mm folks, the only realistic
> path to landing this in the upstream kernel is through these debug
> features.
>
> > Most folks would only use debug during development, if at all -
> > given all the concerns regarding performance. Here, the objective
> > is to enable a powerful security feature set. Hence, the config
> > directives should come under the 'Security Options' menu.
>
> We're not close to having a "Kernel Security" menu, so for now, I've
> wanted to focus on getting the features, and then making the Kconfig
> menus pretty later.
>
> Hopefully that all makes sense! :)
>
> -Kees
>