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

Kaiwan N Billimoria
2017-02-15T07:27:35Z

Okay, I've incorporated your suggestions.
Of course, the printk's are temporary.

Pl see:
- the updated patch, and
- a 'truth table' enumerating some basic testing with these configs,
below:

---
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..fbb4290 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -97,3 +97,24 @@ 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=PAGE_POISON),
+ - page poisoning, equivalent to passing the kernel command-line option
+ 'page_poison=on',
+ irrespective of whether the options are explicitly passed or not.
+
+ If unsure, say N.
+
diff --git a/mm/page_poison.c b/mm/page_poison.c
index 2e647c6..8d1e883 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -49,6 +49,17 @@ struct page_ext_operations page_poisoning_ops = {
.init = init_page_poisoning,
};

+static int __init memory_sanitize_pagepoison_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_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 d24e1ce..62de543 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -457,6 +457,17 @@ static int slub_debug;
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;
+ }
+ 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
@@ -5675,6 +5686,11 @@ 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);

---
(Minimal) Testing done so far:
-------------------------------+----------------------+-----------------------
| Kconfig | kernel cmdline | Result* |
|--------------+---------------+----------------------+----------------------|
SLUB_DEBUG[_ON]|MEMORY_SANITIZE|page_poison|slub_debug|page_poison|slub_debug|
|--------------+---------------+----------------------+----------------------|
Y | Y | np[1] | np | on | p |
Y | Y | np[1] | =p | on | p |
Y | Y | np[1] | =fzu | on | p |
Y | Y | np[1] | =fzup | on | p |
Y | Y | np[1] | = | on | p |
|--------------+---------------+----------------------+----------------------|
Y | Y | =off | np | on | p |
Y | Y | =off | =p | on | p |
Y | Y | =off | =fzu | on | p |
Y | Y | =off | = | on | p |
|--------------+---------------+----------------------+----------------------|
Y | Y | =on | np | on | p |
Y | Y | =on | =p | on | p |
Y | Y | =on | =fzu | on | p |
Y | Y | =on | = | on | p |
|--------------+---------------+----------------------+----------------------|
[1] np = not passed
* Result: MEMORY_SANITIZE='y' => page_poison should be 'on' and slub_debug='p'
(implying SLAB_POISON bit set).
So far, all tests passed..

Thanks,
Kaiwan.

On Tue, 14 Feb 2017 09:19:27 -0800
Kees Cook <keescook@chromium.org> wrote:

> On Mon, Feb 13, 2017 at 7:01 PM, Kaiwan N Billimoria
> <kaiwan@kaiwantech.com> wrote:
> > Thanks for your response...
> >>
> >>
> >>
> >> > +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 ...
> >>
> >> Good start! Why the "if HIBERNATION" bit? It seems like sanity
> >> checks are very expensive, so we'd not want it as part of this
> >> config?
> > Okay, I wasn't sure. So would it be (more) correct to retain the
> > first two configs plus
> > PAGE_POISONING_NO_SANITY (without the if)?
>
> I think so, yes. We may need to tweak it in the future, but I think
> that's the correct config for now.
>
> >> > #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 */
> >>
> >> Could the definition of DEBUG_DEFAULT_FLAGS be adjusted instead of
> >> doing the ifdefs here in the .c file? Or, perhaps do a slub_debug
> >> |= SLAB_POISON in memory_sanitize_init()?
> >>
> > Yes, the latter sounds good but the init function is in
> > mm/page_poison.c and the slub_debug var is a static in mm/slub.c .
> > Any suggestions?
>
> Perhaps add another early_init like you did the page_poison.c?
>
> -Kees
>