@@ -1671,6 +1671,14 @@
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
@@ -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;
}
@@ -2610,6 +2610,28 @@ 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))
+ 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);
+}
+
#ifdef CONFIG_DEBUG_PAGEALLOC
extern bool _debug_pagealloc_enabled;
extern void __kernel_map_pages(struct page *page, int numpages, int enable);
@@ -315,7 +315,7 @@ static struct page *kimage_alloc_pages(gfp_t gfp_mask, unsigned int order)
arch_kexec_post_alloc_pages(page_address(pages), count,
gfp_mask);
- if (gfp_mask & __GFP_ZERO)
+ if (want_init_on_alloc(gfp_mask))
for (i = 0; i < count; i++)
clear_highpage(pages + i);
}
@@ -381,7 +381,7 @@ 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;
@@ -133,6 +133,48 @@ 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
+#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
+DEFINE_STATIC_KEY_TRUE(init_on_free);
+#else
+DEFINE_STATIC_KEY_FALSE(init_on_free);
+#endif
+
+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)
+ 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)
+ 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
@@ -1092,6 +1134,15 @@ 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;
+
+ if (want_init_on_free())
+ 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)
{
@@ -1144,6 +1195,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
}
arch_free_page(page, order);
kernel_poison_pages(page, 1 << order, 0);
+ kernel_init_free_pages(page, 1 << order);
kernel_map_pages(page, 1 << order, 0);
kasan_free_nondeferred_pages(page, order);
@@ -1450,8 +1502,10 @@ meminit_pfn_in_nid(unsigned long pfn, int node,
void __init memblock_free_pages(struct page *page, unsigned long pfn,
unsigned int order)
{
- if (early_page_uninitialised(pfn))
+ if (early_page_uninitialised(pfn)) {
+ kernel_init_free_pages(page, 1 << order);
return;
+ }
__free_pages_core(page, order);
}
@@ -1969,8 +2023,8 @@ 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
@@ -2027,7 +2081,7 @@ static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags
post_alloc_hook(page, order, gfp_flags);
- if (!free_pages_prezeroed() && (gfp_flags & __GFP_ZERO))
+ if (!free_pages_prezeroed() && want_init_on_alloc(gfp_flags))
for (i = 0; i < (1 << order); i++)
clear_highpage(page + i);
@@ -1891,6 +1891,14 @@ 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;
@@ -3330,7 +3338,7 @@ 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);
@@ -3387,7 +3395,7 @@ 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);
@@ -3508,6 +3516,8 @@ 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);
@@ -3595,7 +3605,7 @@ 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);
@@ -524,4 +524,20 @@ 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))
+ return !(c->ctor);
+ else
+ 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);
+ else
+ return false;
+}
+
#endif /* MM_SLAB_H */
@@ -212,6 +212,19 @@ static void slob_free_pages(void *b, int order)
free_pages((unsigned long)b, order);
}
+/*
+ * init_on_free=1 also implies initialization at allocation time.
+ * This is because newly allocated objects may contain freelist pointers
+ * somewhere in the middle.
+ */
+static inline bool slob_want_init_on_alloc(gfp_t flags, struct kmem_cache *c)
+{
+ if (static_branch_unlikely(&init_on_alloc) ||
+ static_branch_unlikely(&init_on_free))
+ return c ? (!c->ctor) : true;
+ return flags & __GFP_ZERO;
+}
+
/*
* Allocate a slob block within a given slob_page sp.
*/
@@ -330,8 +343,6 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
BUG_ON(!b);
spin_unlock_irqrestore(&slob_lock, flags);
}
- if (unlikely(gfp & __GFP_ZERO))
- memset(b, 0, size);
return b;
}
@@ -366,6 +377,9 @@ static void slob_free(void *block, int size)
return;
}
+ if (unlikely(want_init_on_free()))
+ memset(block, 0, size);
+
if (!slob_page_free(sp)) {
/* This slob page is about to become partially free. Easy! */
sp->units = units;
@@ -461,6 +475,8 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
}
kmemleak_alloc(ret, size, 1, gfp);
+ if (unlikely(slob_want_init_on_alloc(gfp, 0)))
+ memset(ret, 0, size);
return ret;
}
@@ -559,6 +575,8 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
WARN_ON_ONCE(flags & __GFP_ZERO);
c->ctor(b);
}
+ if (unlikely(slob_want_init_on_alloc(flags, c)))
+ memset(b, 0, c->size);
kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
return b;
@@ -1432,6 +1432,19 @@ 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;
+
+ if (slab_want_init_on_free(s))
+ do {
+ object = next;
+ next = get_freepointer(s, object);
+ memset(object, 0, s->size);
+ 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.
@@ -1441,9 +1454,7 @@ 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;
@@ -2749,8 +2760,14 @@ 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 (slab_want_init_on_free(s))
+ *(void **)object = 0;
- 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);
@@ -3172,7 +3189,7 @@ 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++)
@@ -1601,7 +1601,7 @@ 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);
@@ -159,6 +159,22 @@ 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 "Set init_on_alloc=1 by default"
+ default false
+ help
+ Enable init_on_alloc=1 by default, making the kernel initialize every
+ page and heap allocation with zeroes.
+ init_on_alloc can be overridden via command line.
+
+config INIT_ON_FREE_DEFAULT_ON
+ bool "Set init_on_free=1 by default"
+ default false
+ help
+ Enable init_on_free=1 by default, making the kernel initialize freed
+ pages and slab memory with zeroes.
+ init_on_free can be overridden via command line.
+
endmenu
endmenu
The new options are needed to prevent possible information leaks and make control-flow bugs that depend on uninitialized values more deterministic. 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 only exception is slab caches with constructors. Those are never zero-initialized to preserve their semantics. For SLOB allocator init_on_free=1 also implies init_on_alloc=1 behavior, i.e. objects are zeroed at both allocation and deallocation time. This is done because SLOB may otherwise return multiple freelist pointers in the allocated object. For SLAB and SLUB enabling either init_on_alloc or init_on_free leads to one-time initialization of the object. 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. 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. Signed-off-by: Alexander Potapenko <glider@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Christoph Lameter <cl@linux.com> Cc: Masahiro Yamada <yamada.masahiro@socionext.com> 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: Kees Cook <keescook@chromium.org> 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: linux-mm@kvack.org Cc: linux-security-module@vger.kernel.org Cc: kernel-hardening@lists.openwall.com --- .../admin-guide/kernel-parameters.txt | 8 +++ drivers/infiniband/core/uverbs_ioctl.c | 2 +- include/linux/mm.h | 22 +++++++ kernel/kexec_core.c | 2 +- mm/dmapool.c | 2 +- mm/page_alloc.c | 62 +++++++++++++++++-- mm/slab.c | 16 ++++- mm/slab.h | 16 +++++ mm/slob.c | 22 ++++++- mm/slub.c | 27 ++++++-- net/core/sock.c | 2 +- security/Kconfig.hardening | 16 +++++ 12 files changed, 179 insertions(+), 18 deletions(-)