[PATCH v10 0/3] add init_on_alloc/init_on_free boot options

[PATCH v10 0/3] add init_on_alloc/init_on_free boot options

[Alexander Potapenko]

Provide init_on_alloc and init_on_free boot options.

These are aimed at preventing possible information leaks and making the
control-flow bugs that depend on uninitialized values more deterministic.

Enabling either of the options guarantees that the memory returned by the
page allocator and SL[AU]B is initialized with zeroes.
SLOB allocator isn't supported at the moment, as its emulation of kmem
caches complicates handling of SLAB_TYPESAFE_BY_RCU caches correctly.

Enabling init_on_free also guarantees that pages and heap objects are
initialized right after they're freed, so it won't be possible to access
stale data by using a dangling pointer.

As suggested by Michal Hocko, right now we don't let the heap users to
disable initialization for certain allocations. There's not enough
evidence that doing so can speed up real-life cases, and introducing
ways to opt-out may result in things going out of control.

To: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux.com>
To: Kees Cook <keescook@chromium.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Sandeep Patil <sspatil@android.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Qian Cai <cai@lca.pw>
Cc: linux-mm@kvack.org
Cc: linux-security-module@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com

Alexander Potapenko (2):
  mm: security: introduce init_on_alloc=1 and init_on_free=1 boot
    options
  mm: init: report memory auto-initialization features at boot time

 .../admin-guide/kernel-parameters.txt         |  9 +++
 drivers/infiniband/core/uverbs_ioctl.c        |  2 +-
 include/linux/mm.h                            | 24 +++++++
 init/main.c                                   | 24 +++++++
 mm/dmapool.c                                  |  4 +-
 mm/page_alloc.c                               | 71 +++++++++++++++++--
 mm/slab.c                                     | 16 ++++-
 mm/slab.h                                     | 20 ++++++
 mm/slub.c                                     | 40 +++++++++--
 net/core/sock.c                               |  2 +-
 security/Kconfig.hardening                    | 29 ++++++++
 11 files changed, 223 insertions(+), 18 deletions(-)
---
 v3: dropped __GFP_NO_AUTOINIT patches
 v5: dropped support for SLOB allocator, handle SLAB_TYPESAFE_BY_RCU
 v6: changed wording in boot-time message
 v7: dropped the test_meminit.c patch (picked by Andrew Morton already),
     minor wording changes
 v8: fixes for interoperability with other heap debugging features
 v9: added support for page/slab poisoning
 v10: changed pr_warn() to pr_info(), added Acked-by: tags
-- 
2.22.0.410.gd8fdbe21b5-goog

[PATCH v10 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options

[Alexander Potapenko]

The new options are needed to prevent possible information leaks and
make control-flow bugs that depend on uninitialized values more
deterministic.

This is expected to be on-by-default on Android and Chrome OS. And it
gives the opportunity for anyone else to use it under distros too via
the boot args. (The init_on_free feature is regularly requested by
folks where memory forensics is included in their threat models.)

init_on_alloc=1 makes the kernel initialize newly allocated pages and heap
objects with zeroes. Initialization is done at allocation time at the
places where checks for __GFP_ZERO are performed.

init_on_free=1 makes the kernel initialize freed pages and heap objects
with zeroes upon their deletion. This helps to ensure sensitive data
doesn't leak via use-after-free accesses.

Both init_on_alloc=1 and init_on_free=1 guarantee that the allocator
returns zeroed memory. The two exceptions are slab caches with
constructors and SLAB_TYPESAFE_BY_RCU flag. Those are never
zero-initialized to preserve their semantics.

Both init_on_alloc and init_on_free default to zero, but those defaults
can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and
CONFIG_INIT_ON_FREE_DEFAULT_ON.

If either SLUB poisoning or page poisoning is enabled, those options
take precedence over init_on_alloc and init_on_free: initialization is
only applied to unpoisoned allocations.

Slowdown for the new features compared to init_on_free=0,
init_on_alloc=0:

hackbench, init_on_free=1:  +7.62% sys time (st.err 0.74%)
hackbench, init_on_alloc=1: +7.75% sys time (st.err 2.14%)

Linux build with -j12, init_on_free=1:  +8.38% wall time (st.err 0.39%)
Linux build with -j12, init_on_free=1:  +24.42% sys time (st.err 0.52%)
Linux build with -j12, init_on_alloc=1: -0.13% wall time (st.err 0.42%)
Linux build with -j12, init_on_alloc=1: +0.57% sys time (st.err 0.40%)

The slowdown for init_on_free=0, init_on_alloc=0 compared to the
baseline is within the standard error.

The new features are also going to pave the way for hardware memory
tagging (e.g. arm64's MTE), which will require both on_alloc and on_free
hooks to set the tags for heap objects. With MTE, tagging will have the
same cost as memory initialization.

Although init_on_free is rather costly, there are paranoid use-cases where
in-memory data lifetime is desired to be minimized. There are various
arguments for/against the realism of the associated threat models, but
given that we'll need the infrastructure for MTE anyway, and there are
people who want wipe-on-free behavior no matter what the performance cost,
it seems reasonable to include it in this series.

Signed-off-by: Alexander Potapenko <glider@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: James Morris <jamorris@linux.microsoft.com>
To: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux.com>
To: Kees Cook <keescook@chromium.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Sandeep Patil <sspatil@android.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Qian Cai <cai@lca.pw>
Cc: James Morris <jamorris@linux.microsoft.com>
Cc: linux-mm@kvack.org
Cc: linux-security-module@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 v2:
  - unconditionally initialize pages in kernel_init_free_pages()
  - comment from Randy Dunlap: drop 'default false' lines from Kconfig.hardening
 v3:
  - don't call kernel_init_free_pages() from memblock_free_pages()
  - adopted some Kees' comments for the patch description
 v4:
  - use NULL instead of 0 in slab_alloc_node() (found by kbuild test robot)
  - don't write to NULL object in slab_alloc_node() (found by Android
    testing)
 v5:
  - adjusted documentation wording as suggested by Kees
  - disable SLAB_POISON if auto-initialization is on
  - don't wipe RCU cache allocations made without __GFP_ZERO
  - dropped SLOB support
 v7:
  - rebase the patch, added the Acked-by: tag
 v8:
  - addressed comments by Michal Hocko: revert kernel/kexec_core.c and
    apply initialization in dma_pool_free()
  - disable init_on_alloc/init_on_free if slab poisoning or page
    poisoning are enabled, as requested by Qian Cai
  - skip the redzone when initializing a freed heap object, as requested
    by Qian Cai and Kees Cook
  - use s->offset to address the freeptr (suggested by Kees Cook)
  - updated the patch description, added Signed-off-by: tag
 v9:
  - picked up -mm fixes from Qian Cai and Andrew Morton (order of calls
    in free_pages_prepare(), export init_on_alloc)
  - exported init_on_free
  - allowed using init_on_alloc/init_on_free with SLUB poisoning and
    page poisoning. Poisoning supersedes zero-initialization, so some
    tests may behave differently with poisoning enabled.
 v10:
  - added Acked-by: tags
  - converted pr_warn() to pr_info()
---
 .../admin-guide/kernel-parameters.txt         |  9 +++
 drivers/infiniband/core/uverbs_ioctl.c        |  2 +-
 include/linux/mm.h                            | 24 +++++++
 mm/dmapool.c                                  |  4 +-
 mm/page_alloc.c                               | 71 +++++++++++++++++--
 mm/slab.c                                     | 16 ++++-
 mm/slab.h                                     | 20 ++++++
 mm/slub.c                                     | 40 +++++++++--
 net/core/sock.c                               |  2 +-
 security/Kconfig.hardening                    | 29 ++++++++
 10 files changed, 199 insertions(+), 18 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f6664b2e2..84ee1121a2b9 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1673,6 +1673,15 @@
 
 	initrd=		[BOOT] Specify the location of the initial ramdisk
 
+	init_on_alloc=	[MM] Fill newly allocated pages and heap objects with
+			zeroes.
+			Format: 0 | 1
+			Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
+
+	init_on_free=	[MM] Fill freed pages and heap objects with zeroes.
+			Format: 0 | 1
+			Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
+
 	init_pkru=	[x86] Specify the default memory protection keys rights
 			register contents for all processes.  0x55555554 by
 			default (disallow access to all but pkey 0).  Can
diff --git a/drivers/infiniband/core/uverbs_ioctl.c b/drivers/infiniband/core/uverbs_ioctl.c
index 829b0c6944d8..61758201d9b2 100644
--- a/drivers/infiniband/core/uverbs_ioctl.c
+++ b/drivers/infiniband/core/uverbs_ioctl.c
@@ -127,7 +127,7 @@ __malloc void *_uverbs_alloc(struct uverbs_attr_bundle *bundle, size_t size,
 	res = (void *)pbundle->internal_buffer + pbundle->internal_used;
 	pbundle->internal_used =
 		ALIGN(new_used, sizeof(*pbundle->internal_buffer));
-	if (flags & __GFP_ZERO)
+	if (want_init_on_alloc(flags))
 		memset(res, 0, size);
 	return res;
 }
diff --git a/include/linux/mm.h b/include/linux/mm.h
index dd0b5f4e1e45..81b582657854 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2696,6 +2696,30 @@ static inline void kernel_poison_pages(struct page *page, int numpages,
 					int enable) { }
 #endif
 
+#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
+DECLARE_STATIC_KEY_TRUE(init_on_alloc);
+#else
+DECLARE_STATIC_KEY_FALSE(init_on_alloc);
+#endif
+static inline bool want_init_on_alloc(gfp_t flags)
+{
+	if (static_branch_unlikely(&init_on_alloc) &&
+	    !page_poisoning_enabled())
+		return true;
+	return flags & __GFP_ZERO;
+}
+
+#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
+DECLARE_STATIC_KEY_TRUE(init_on_free);
+#else
+DECLARE_STATIC_KEY_FALSE(init_on_free);
+#endif
+static inline bool want_init_on_free(void)
+{
+	return static_branch_unlikely(&init_on_free) &&
+	       !page_poisoning_enabled();
+}
+
 extern bool _debug_pagealloc_enabled;
 
 static inline bool debug_pagealloc_enabled(void)
diff --git a/mm/dmapool.c b/mm/dmapool.c
index 8c94c89a6f7e..fe5d33060415 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -378,7 +378,7 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
 #endif
 	spin_unlock_irqrestore(&pool->lock, flags);
 
-	if (mem_flags & __GFP_ZERO)
+	if (want_init_on_alloc(mem_flags))
 		memset(retval, 0, pool->size);
 
 	return retval;
@@ -428,6 +428,8 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 	}
 
 	offset = vaddr - page->vaddr;
+	if (want_init_on_free())
+		memset(vaddr, 0, pool->size);
 #ifdef	DMAPOOL_DEBUG
 	if ((dma - page->dma) != offset) {
 		spin_unlock_irqrestore(&pool->lock, flags);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d66bc8abe0af..4a43fa59c53c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -136,6 +136,55 @@ unsigned long totalcma_pages __read_mostly;
 
 int percpu_pagelist_fraction;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
+#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
+DEFINE_STATIC_KEY_TRUE(init_on_alloc);
+#else
+DEFINE_STATIC_KEY_FALSE(init_on_alloc);
+#endif
+EXPORT_SYMBOL(init_on_alloc);
+
+#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
+DEFINE_STATIC_KEY_TRUE(init_on_free);
+#else
+DEFINE_STATIC_KEY_FALSE(init_on_free);
+#endif
+EXPORT_SYMBOL(init_on_free);
+
+static int __init early_init_on_alloc(char *buf)
+{
+	int ret;
+	bool bool_result;
+
+	if (!buf)
+		return -EINVAL;
+	ret = kstrtobool(buf, &bool_result);
+	if (bool_result && page_poisoning_enabled())
+		pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n");
+	if (bool_result)
+		static_branch_enable(&init_on_alloc);
+	else
+		static_branch_disable(&init_on_alloc);
+	return ret;
+}
+early_param("init_on_alloc", early_init_on_alloc);
+
+static int __init early_init_on_free(char *buf)
+{
+	int ret;
+	bool bool_result;
+
+	if (!buf)
+		return -EINVAL;
+	ret = kstrtobool(buf, &bool_result);
+	if (bool_result && page_poisoning_enabled())
+		pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n");
+	if (bool_result)
+		static_branch_enable(&init_on_free);
+	else
+		static_branch_disable(&init_on_free);
+	return ret;
+}
+early_param("init_on_free", early_init_on_free);
 
 /*
  * A cached value of the page's pageblock's migratetype, used when the page is
@@ -1090,6 +1139,14 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
 	return ret;
 }
 
+static void kernel_init_free_pages(struct page *page, int numpages)
+{
+	int i;
+
+	for (i = 0; i < numpages; i++)
+		clear_highpage(page + i);
+}
+
 static __always_inline bool free_pages_prepare(struct page *page,
 					unsigned int order, bool check_free)
 {
@@ -1141,6 +1198,9 @@ static __always_inline bool free_pages_prepare(struct page *page,
 					   PAGE_SIZE << order);
 	}
 	arch_free_page(page, order);
+	if (want_init_on_free())
+		kernel_init_free_pages(page, 1 << order);
+
 	kernel_poison_pages(page, 1 << order, 0);
 	if (debug_pagealloc_enabled())
 		kernel_map_pages(page, 1 << order, 0);
@@ -2020,8 +2080,8 @@ static inline int check_new_page(struct page *page)
 
 static inline bool free_pages_prezeroed(void)
 {
-	return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
-		page_poisoning_enabled();
+	return (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
+		page_poisoning_enabled()) || want_init_on_free();
 }
 
 #ifdef CONFIG_DEBUG_VM
@@ -2075,13 +2135,10 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 							unsigned int alloc_flags)
 {
-	int i;
-
 	post_alloc_hook(page, order, gfp_flags);
 
-	if (!free_pages_prezeroed() && (gfp_flags & __GFP_ZERO))
-		for (i = 0; i < (1 << order); i++)
-			clear_highpage(page + i);
+	if (!free_pages_prezeroed() && want_init_on_alloc(gfp_flags))
+		kernel_init_free_pages(page, 1 << order);
 
 	if (order && (gfp_flags & __GFP_COMP))
 		prep_compound_page(page, order);
diff --git a/mm/slab.c b/mm/slab.c
index f7117ad9b3a3..98a89d7c922d 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1830,6 +1830,14 @@ static bool set_objfreelist_slab_cache(struct kmem_cache *cachep,
 
 	cachep->num = 0;
 
+	/*
+	 * If slab auto-initialization on free is enabled, store the freelist
+	 * off-slab, so that its contents don't end up in one of the allocated
+	 * objects.
+	 */
+	if (unlikely(slab_want_init_on_free(cachep)))
+		return false;
+
 	if (cachep->ctor || flags & SLAB_TYPESAFE_BY_RCU)
 		return false;
 
@@ -3263,7 +3271,7 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
 	local_irq_restore(save_flags);
 	ptr = cache_alloc_debugcheck_after(cachep, flags, ptr, caller);
 
-	if (unlikely(flags & __GFP_ZERO) && ptr)
+	if (unlikely(slab_want_init_on_alloc(flags, cachep)) && ptr)
 		memset(ptr, 0, cachep->object_size);
 
 	slab_post_alloc_hook(cachep, flags, 1, &ptr);
@@ -3320,7 +3328,7 @@ slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller)
 	objp = cache_alloc_debugcheck_after(cachep, flags, objp, caller);
 	prefetchw(objp);
 
-	if (unlikely(flags & __GFP_ZERO) && objp)
+	if (unlikely(slab_want_init_on_alloc(flags, cachep)) && objp)
 		memset(objp, 0, cachep->object_size);
 
 	slab_post_alloc_hook(cachep, flags, 1, &objp);
@@ -3441,6 +3449,8 @@ void ___cache_free(struct kmem_cache *cachep, void *objp,
 	struct array_cache *ac = cpu_cache_get(cachep);
 
 	check_irq_off();
+	if (unlikely(slab_want_init_on_free(cachep)))
+		memset(objp, 0, cachep->object_size);
 	kmemleak_free_recursive(objp, cachep->flags);
 	objp = cache_free_debugcheck(cachep, objp, caller);
 
@@ -3528,7 +3538,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 	cache_alloc_debugcheck_after_bulk(s, flags, size, p, _RET_IP_);
 
 	/* Clear memory outside IRQ disabled section */
-	if (unlikely(flags & __GFP_ZERO))
+	if (unlikely(slab_want_init_on_alloc(flags, s)))
 		for (i = 0; i < size; i++)
 			memset(p[i], 0, s->object_size);
 
diff --git a/mm/slab.h b/mm/slab.h
index 43ac818b8592..d3f585e604bb 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -524,4 +524,24 @@ static inline int cache_random_seq_create(struct kmem_cache *cachep,
 static inline void cache_random_seq_destroy(struct kmem_cache *cachep) { }
 #endif /* CONFIG_SLAB_FREELIST_RANDOM */
 
+static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c)
+{
+	if (static_branch_unlikely(&init_on_alloc)) {
+		if (c->ctor)
+			return false;
+		if (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON))
+			return flags & __GFP_ZERO;
+		return true;
+	}
+	return flags & __GFP_ZERO;
+}
+
+static inline bool slab_want_init_on_free(struct kmem_cache *c)
+{
+	if (static_branch_unlikely(&init_on_free))
+		return !(c->ctor ||
+			 (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)));
+	return false;
+}
+
 #endif /* MM_SLAB_H */
diff --git a/mm/slub.c b/mm/slub.c
index cd04dbd2b5d0..199ce29cbbcb 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1279,6 +1279,10 @@ static int __init setup_slub_debug(char *str)
 	if (*str == ',')
 		slub_debug_slabs = str + 1;
 out:
+	if ((static_branch_unlikely(&init_on_alloc) ||
+	     static_branch_unlikely(&init_on_free)) &&
+	    (slub_debug & SLAB_POISON))
+		pr_info("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n");
 	return 1;
 }
 
@@ -1424,6 +1428,28 @@ static __always_inline bool slab_free_hook(struct kmem_cache *s, void *x)
 static inline bool slab_free_freelist_hook(struct kmem_cache *s,
 					   void **head, void **tail)
 {
+
+	void *object;
+	void *next = *head;
+	void *old_tail = *tail ? *tail : *head;
+	int rsize;
+
+	if (slab_want_init_on_free(s))
+		do {
+			object = next;
+			next = get_freepointer(s, object);
+			/*
+			 * Clear the object and the metadata, but don't touch
+			 * the redzone.
+			 */
+			memset(object, 0, s->object_size);
+			rsize = (s->flags & SLAB_RED_ZONE) ? s->red_left_pad
+							   : 0;
+			memset((char *)object + s->inuse, 0,
+			       s->size - s->inuse - rsize);
+			set_freepointer(s, object, next);
+		} while (object != old_tail);
+
 /*
  * Compiler cannot detect this function can be removed if slab_free_hook()
  * evaluates to nothing.  Thus, catch all relevant config debug options here.
@@ -1433,9 +1459,7 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s,
 	defined(CONFIG_DEBUG_OBJECTS_FREE) ||	\
 	defined(CONFIG_KASAN)
 
-	void *object;
-	void *next = *head;
-	void *old_tail = *tail ? *tail : *head;
+	next = *head;
 
 	/* Head and tail of the reconstructed freelist */
 	*head = NULL;
@@ -2741,8 +2765,14 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
 		prefetch_freepointer(s, next_object);
 		stat(s, ALLOC_FASTPATH);
 	}
+	/*
+	 * If the object has been wiped upon free, make sure it's fully
+	 * initialized by zeroing out freelist pointer.
+	 */
+	if (unlikely(slab_want_init_on_free(s)) && object)
+		memset(object + s->offset, 0, sizeof(void *));
 
-	if (unlikely(gfpflags & __GFP_ZERO) && object)
+	if (unlikely(slab_want_init_on_alloc(gfpflags, s)) && object)
 		memset(object, 0, s->object_size);
 
 	slab_post_alloc_hook(s, gfpflags, 1, &object);
@@ -3163,7 +3193,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 	local_irq_enable();
 
 	/* Clear memory outside IRQ disabled fastpath loop */
-	if (unlikely(flags & __GFP_ZERO)) {
+	if (unlikely(slab_want_init_on_alloc(flags, s))) {
 		int j;
 
 		for (j = 0; j < i; j++)
diff --git a/net/core/sock.c b/net/core/sock.c
index af09a23e4822..425e97f693ce 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1596,7 +1596,7 @@ static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,
 		sk = kmem_cache_alloc(slab, priority & ~__GFP_ZERO);
 		if (!sk)
 			return sk;
-		if (priority & __GFP_ZERO)
+		if (want_init_on_alloc(priority))
 			sk_prot_clear_nulls(sk, prot->obj_size);
 	} else
 		sk = kmalloc(prot->obj_size, priority);
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index c6cb2d9b2905..a1ffe2eb4d5f 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -160,6 +160,35 @@ config STACKLEAK_RUNTIME_DISABLE
 	  runtime to control kernel stack erasing for kernels built with
 	  CONFIG_GCC_PLUGIN_STACKLEAK.
 
+config INIT_ON_ALLOC_DEFAULT_ON
+	bool "Enable heap memory zeroing on allocation by default"
+	help
+	  This has the effect of setting "init_on_alloc=1" on the kernel
+	  command line. This can be disabled with "init_on_alloc=0".
+	  When "init_on_alloc" is enabled, all page allocator and slab
+	  allocator memory will be zeroed when allocated, eliminating
+	  many kinds of "uninitialized heap memory" flaws, especially
+	  heap content exposures. The performance impact varies by
+	  workload, but most cases see <1% impact. Some synthetic
+	  workloads have measured as high as 7%.
+
+config INIT_ON_FREE_DEFAULT_ON
+	bool "Enable heap memory zeroing on free by default"
+	help
+	  This has the effect of setting "init_on_free=1" on the kernel
+	  command line. This can be disabled with "init_on_free=0".
+	  Similar to "init_on_alloc", when "init_on_free" is enabled,
+	  all page allocator and slab allocator memory will be zeroed
+	  when freed, eliminating many kinds of "uninitialized heap memory"
+	  flaws, especially heap content exposures. The primary difference
+	  with "init_on_free" is that data lifetime in memory is reduced,
+	  as anything freed is wiped immediately, making live forensics or
+	  cold boot memory attacks unable to recover freed memory contents.
+	  The performance impact varies by workload, but is more expensive
+	  than "init_on_alloc" due to the negative cache effects of
+	  touching "cold" memory areas. Most cases see 3-5% impact. Some
+	  synthetic workloads have measured as high as 8%.
+
 endmenu
 
 endmenu
-- 
2.22.0.410.gd8fdbe21b5-goog

Re: [PATCH v10 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options

[Andrew Morton]

On Fri, 28 Jun 2019 11:31:30 +0200 Alexander Potapenko <glider@google.com> wrote:

> The new options are needed to prevent possible information leaks and
> make control-flow bugs that depend on uninitialized values more
> deterministic.
> 
> This is expected to be on-by-default on Android and Chrome OS. And it
> gives the opportunity for anyone else to use it under distros too via
> the boot args. (The init_on_free feature is regularly requested by
> folks where memory forensics is included in their threat models.)
> 
> init_on_alloc=1 makes the kernel initialize newly allocated pages and heap
> objects with zeroes. Initialization is done at allocation time at the
> places where checks for __GFP_ZERO are performed.
> 
> init_on_free=1 makes the kernel initialize freed pages and heap objects
> with zeroes upon their deletion. This helps to ensure sensitive data
> doesn't leak via use-after-free accesses.
> 
> Both init_on_alloc=1 and init_on_free=1 guarantee that the allocator
> returns zeroed memory. The two exceptions are slab caches with
> constructors and SLAB_TYPESAFE_BY_RCU flag. Those are never
> zero-initialized to preserve their semantics.
> 
> Both init_on_alloc and init_on_free default to zero, but those defaults
> can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and
> CONFIG_INIT_ON_FREE_DEFAULT_ON.
> 
> If either SLUB poisoning or page poisoning is enabled, those options
> take precedence over init_on_alloc and init_on_free: initialization is
> only applied to unpoisoned allocations.
> 
> Slowdown for the new features compared to init_on_free=0,
> init_on_alloc=0:
> 
> hackbench, init_on_free=1:  +7.62% sys time (st.err 0.74%)
> hackbench, init_on_alloc=1: +7.75% sys time (st.err 2.14%)
> 
> Linux build with -j12, init_on_free=1:  +8.38% wall time (st.err 0.39%)
> Linux build with -j12, init_on_free=1:  +24.42% sys time (st.err 0.52%)
> Linux build with -j12, init_on_alloc=1: -0.13% wall time (st.err 0.42%)
> Linux build with -j12, init_on_alloc=1: +0.57% sys time (st.err 0.40%)
> 
> The slowdown for init_on_free=0, init_on_alloc=0 compared to the
> baseline is within the standard error.
> 
> The new features are also going to pave the way for hardware memory
> tagging (e.g. arm64's MTE), which will require both on_alloc and on_free
> hooks to set the tags for heap objects. With MTE, tagging will have the
> same cost as memory initialization.
> 
> Although init_on_free is rather costly, there are paranoid use-cases where
> in-memory data lifetime is desired to be minimized. There are various
> arguments for/against the realism of the associated threat models, but
> given that we'll need the infrastructure for MTE anyway, and there are
> people who want wipe-on-free behavior no matter what the performance cost,
> it seems reasonable to include it in this series.
>
> ...
>
>  v10:
>   - added Acked-by: tags
>   - converted pr_warn() to pr_info()

There are unchangelogged alterations between v9 and v10.  The
replacement of IS_ENABLED(CONFIG_PAGE_POISONING)) with
page_poisoning_enabled().


--- a/mm/page_alloc.c~mm-security-introduce-init_on_alloc=1-and-init_on_free=1-boot-options-v10
+++ a/mm/page_alloc.c
@@ -157,8 +157,8 @@ static int __init early_init_on_alloc(ch
 	if (!buf)
 		return -EINVAL;
 	ret = kstrtobool(buf, &bool_result);
-	if (bool_result && IS_ENABLED(CONFIG_PAGE_POISONING))
-		pr_warn("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n");
+	if (bool_result && page_poisoning_enabled())
+		pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n");
 	if (bool_result)
 		static_branch_enable(&init_on_alloc);
 	else
@@ -175,8 +175,8 @@ static int __init early_init_on_free(cha
 	if (!buf)
 		return -EINVAL;
 	ret = kstrtobool(buf, &bool_result);
-	if (bool_result && IS_ENABLED(CONFIG_PAGE_POISONING))
-		pr_warn("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n");
+	if (bool_result && page_poisoning_enabled())
+		pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n");
 	if (bool_result)
 		static_branch_enable(&init_on_free);
 	else
--- a/mm/slub.c~mm-security-introduce-init_on_alloc=1-and-init_on_free=1-boot-options-v10
+++ a/mm/slub.c
@@ -1281,9 +1281,8 @@ check_slabs:
 out:
 	if ((static_branch_unlikely(&init_on_alloc) ||
 	     static_branch_unlikely(&init_on_free)) &&
-	    (slub_debug & SLAB_POISON)) {
-		pr_warn("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n");
-	}
+	    (slub_debug & SLAB_POISON))
+		pr_info("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n");
 	return 1;
 }
 
_

Re: [PATCH v10 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options

[Alexander Potapenko]

On Wed, Jul 3, 2019 at 12:59 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Fri, 28 Jun 2019 11:31:30 +0200 Alexander Potapenko <glider@google.com> wrote:
>
> > The new options are needed to prevent possible information leaks and
> > make control-flow bugs that depend on uninitialized values more
> > deterministic.
> >
> > This is expected to be on-by-default on Android and Chrome OS. And it
> > gives the opportunity for anyone else to use it under distros too via
> > the boot args. (The init_on_free feature is regularly requested by
> > folks where memory forensics is included in their threat models.)
> >
> > init_on_alloc=1 makes the kernel initialize newly allocated pages and heap
> > objects with zeroes. Initialization is done at allocation time at the
> > places where checks for __GFP_ZERO are performed.
> >
> > init_on_free=1 makes the kernel initialize freed pages and heap objects
> > with zeroes upon their deletion. This helps to ensure sensitive data
> > doesn't leak via use-after-free accesses.
> >
> > Both init_on_alloc=1 and init_on_free=1 guarantee that the allocator
> > returns zeroed memory. The two exceptions are slab caches with
> > constructors and SLAB_TYPESAFE_BY_RCU flag. Those are never
> > zero-initialized to preserve their semantics.
> >
> > Both init_on_alloc and init_on_free default to zero, but those defaults
> > can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and
> > CONFIG_INIT_ON_FREE_DEFAULT_ON.
> >
> > If either SLUB poisoning or page poisoning is enabled, those options
> > take precedence over init_on_alloc and init_on_free: initialization is
> > only applied to unpoisoned allocations.
> >
> > Slowdown for the new features compared to init_on_free=0,
> > init_on_alloc=0:
> >
> > hackbench, init_on_free=1:  +7.62% sys time (st.err 0.74%)
> > hackbench, init_on_alloc=1: +7.75% sys time (st.err 2.14%)
> >
> > Linux build with -j12, init_on_free=1:  +8.38% wall time (st.err 0.39%)
> > Linux build with -j12, init_on_free=1:  +24.42% sys time (st.err 0.52%)
> > Linux build with -j12, init_on_alloc=1: -0.13% wall time (st.err 0.42%)
> > Linux build with -j12, init_on_alloc=1: +0.57% sys time (st.err 0.40%)
> >
> > The slowdown for init_on_free=0, init_on_alloc=0 compared to the
> > baseline is within the standard error.
> >
> > The new features are also going to pave the way for hardware memory
> > tagging (e.g. arm64's MTE), which will require both on_alloc and on_free
> > hooks to set the tags for heap objects. With MTE, tagging will have the
> > same cost as memory initialization.
> >
> > Although init_on_free is rather costly, there are paranoid use-cases where
> > in-memory data lifetime is desired to be minimized. There are various
> > arguments for/against the realism of the associated threat models, but
> > given that we'll need the infrastructure for MTE anyway, and there are
> > people who want wipe-on-free behavior no matter what the performance cost,
> > it seems reasonable to include it in this series.
> >
> > ...
> >
> >  v10:
> >   - added Acked-by: tags
> >   - converted pr_warn() to pr_info()
>
> There are unchangelogged alterations between v9 and v10.  The
> replacement of IS_ENABLED(CONFIG_PAGE_POISONING)) with
> page_poisoning_enabled().
In the case I send another version of the patch, do I need to
retroactively add them to the changelog?
>
> --- a/mm/page_alloc.c~mm-security-introduce-init_on_alloc=1-and-init_on_free=1-boot-options-v10
> +++ a/mm/page_alloc.c
> @@ -157,8 +157,8 @@ static int __init early_init_on_alloc(ch
>         if (!buf)
>                 return -EINVAL;
>         ret = kstrtobool(buf, &bool_result);
> -       if (bool_result && IS_ENABLED(CONFIG_PAGE_POISONING))
> -               pr_warn("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n");
> +       if (bool_result && page_poisoning_enabled())
> +               pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n");
>         if (bool_result)
>                 static_branch_enable(&init_on_alloc);
>         else
> @@ -175,8 +175,8 @@ static int __init early_init_on_free(cha
>         if (!buf)
>                 return -EINVAL;
>         ret = kstrtobool(buf, &bool_result);
> -       if (bool_result && IS_ENABLED(CONFIG_PAGE_POISONING))
> -               pr_warn("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n");
> +       if (bool_result && page_poisoning_enabled())
> +               pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n");
>         if (bool_result)
>                 static_branch_enable(&init_on_free);
>         else
> --- a/mm/slub.c~mm-security-introduce-init_on_alloc=1-and-init_on_free=1-boot-options-v10
> +++ a/mm/slub.c
> @@ -1281,9 +1281,8 @@ check_slabs:
>  out:
>         if ((static_branch_unlikely(&init_on_alloc) ||
>              static_branch_unlikely(&init_on_free)) &&
> -           (slub_debug & SLAB_POISON)) {
> -               pr_warn("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n");
> -       }
> +           (slub_debug & SLAB_POISON))
> +               pr_info("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n");
>         return 1;
>  }
>
> _
>


-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

Re: [PATCH v10 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options

[Andrew Morton]

On Wed, 3 Jul 2019 13:40:26 +0200 Alexander Potapenko <glider@google.com> wrote:

> > There are unchangelogged alterations between v9 and v10.  The
> > replacement of IS_ENABLED(CONFIG_PAGE_POISONING)) with
> > page_poisoning_enabled().
> In the case I send another version of the patch, do I need to
> retroactively add them to the changelog?

I don't think the world could stand another version ;)

Please simply explain this change for the reviewers?

Re: [PATCH v10 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options

[Alexander Potapenko]

On Thu, Jul 4, 2019 at 9:53 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Wed, 3 Jul 2019 13:40:26 +0200 Alexander Potapenko <glider@google.com> wrote:
>
> > > There are unchangelogged alterations between v9 and v10.  The
> > > replacement of IS_ENABLED(CONFIG_PAGE_POISONING)) with
> > > page_poisoning_enabled().
> > In the case I send another version of the patch, do I need to
> > retroactively add them to the changelog?
>
> I don't think the world could stand another version ;)
>
> Please simply explain this change for the reviewers?

As Qian Cai mentioned in the comments to v9:

> Yes, only checking CONFIG_PAGE_POISONING is not enough, and need to check
> page_poisoning_enabled().

Actually, page_poisoning_enabled() is enough, because it checks for
CONFIG_PAGE_POISONING itself.
Therefore I've just replaced IS_ENABLED(CONFIG_PAGE_POISONING)) with
page_poisoning_enabled().

-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

[PATCH v10 2/2] mm: init: report memory auto-initialization features at boot time

[Alexander Potapenko]

Print the currently enabled stack and heap initialization modes.

Stack initialization is enabled by a config flag, while heap
initialization is configured at boot time with defaults being set
in the config. It's more convenient for the user to have all information
about these hardening measures in one place at boot, so the user can
reason about the expected behavior of the running system.

The possible options for stack are:
 - "all" for CONFIG_INIT_STACK_ALL;
 - "byref_all" for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL;
 - "byref" for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF;
 - "__user" for CONFIG_GCC_PLUGIN_STRUCTLEAK_USER;
 - "off" otherwise.

Depending on the values of init_on_alloc and init_on_free boottime
options we also report "heap alloc" and "heap free" as "on"/"off".

In the init_on_free mode initializing pages at boot time may take a
while, so print a notice about that as well. This depends on how much
memory is installed, the memory bandwidth, etc.
On a relatively modern x86 system, it takes about 0.75s/GB to wipe all
memory:

  [    0.418722] mem auto-init: stack:byref_all, heap alloc:off, heap free:on
  [    0.419765] mem auto-init: clearing system memory may take some time...
  [   12.376605] Memory: 16408564K/16776672K available (14339K kernel code, 1397K rwdata, 3756K rodata, 1636K init, 11460K bss, 368108K reserved, 0K cma-reserved)

Signed-off-by: Alexander Potapenko <glider@google.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Sandeep Patil <sspatil@android.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: Kaiwan N Billimoria <kaiwan@kaiwantech.com>
Cc: kernel-hardening@lists.openwall.com
Cc: linux-mm@kvack.org
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

---
 v6:
 - update patch description, fixed message about clearing memory
 v7:
 - rebase the patch, add the Acked-by: tag;
 - more description updates as suggested by Kees;
 - make report_meminit() static.
 v8:
 - added the Signed-off-by: tag
---
 init/main.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/init/main.c b/init/main.c
index 66a196c5e4c3..ff5803b0841c 100644
--- a/init/main.c
+++ b/init/main.c
@@ -520,6 +520,29 @@ static inline void initcall_debug_enable(void)
 }
 #endif
 
+/* Report memory auto-initialization states for this boot. */
+static void __init report_meminit(void)
+{
+	const char *stack;
+
+	if (IS_ENABLED(CONFIG_INIT_STACK_ALL))
+		stack = "all";
+	else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL))
+		stack = "byref_all";
+	else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF))
+		stack = "byref";
+	else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_USER))
+		stack = "__user";
+	else
+		stack = "off";
+
+	pr_info("mem auto-init: stack:%s, heap alloc:%s, heap free:%s\n",
+		stack, want_init_on_alloc(GFP_KERNEL) ? "on" : "off",
+		want_init_on_free() ? "on" : "off");
+	if (want_init_on_free())
+		pr_info("mem auto-init: clearing system memory may take some time...\n");
+}
+
 /*
  * Set up kernel memory allocators
  */
@@ -530,6 +553,7 @@ static void __init mm_init(void)
 	 * bigger than MAX_ORDER unless SPARSEMEM.
 	 */
 	page_ext_init_flatmem();
+	report_meminit();
 	mem_init();
 	kmem_cache_init();
 	pgtable_init();
-- 
2.22.0.410.gd8fdbe21b5-goog