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Date: Thu, 23 May 2019 16:01:43 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, 
	Kees Cook <keescook@...omium.org>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>, 
	Linux Memory Management List <linux-mm@...ck.org>, 
	linux-security-module <linux-security-module@...r.kernel.org>, 
	Masahiro Yamada <yamada.masahiro@...ionext.com>, Michal Hocko <mhocko@...nel.org>, 
	James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Kostya Serebryany <kcc@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Sandeep Patil <sspatil@...roid.com>, 
	Laura Abbott <labbott@...hat.com>, Randy Dunlap <rdunlap@...radead.org>, Jann Horn <jannh@...gle.com>, 
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v3 1/3] mm: security: introduce init_on_alloc=1 and
 init_on_free=1 boot options

On Thu, May 23, 2019 at 2:42 PM Alexander Potapenko <glider@...gle.com> wrote:
>
> 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.
>
> 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 infrastructre 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@...gle.com>
> To: Andrew Morton <akpm@...ux-foundation.org>
> To: Christoph Lameter <cl@...ux.com>
> To: Kees Cook <keescook@...omium.org>
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: James Morris <jmorris@...ei.org>
> Cc: "Serge E. Hallyn" <serge@...lyn.com>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Kostya Serebryany <kcc@...gle.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Sandeep Patil <sspatil@...roid.com>
> Cc: Laura Abbott <labbott@...hat.com>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: linux-mm@...ck.org
> Cc: linux-security-module@...r.kernel.org
> Cc: kernel-hardening@...ts.openwall.com
> ---
>  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
> ---
>  .../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                               | 63 ++++++++++++++++---
>  mm/slab.c                                     | 16 ++++-
>  mm/slab.h                                     | 16 +++++
>  mm/slob.c                                     | 22 ++++++-
>  mm/slub.c                                     | 27 ++++++--
>  net/core/sock.c                               |  2 +-
>  security/Kconfig.hardening                    | 14 +++++
>  12 files changed, 175 insertions(+), 21 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 52e6fbb042cc..68fb6fa41cc1 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1673,6 +1673,14 @@
>
>         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
> 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 0e8834ac32b7..7733a341c0c4 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2685,6 +2685,28 @@ 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);
> +}
> +
>  extern bool _debug_pagealloc_enabled;
>
>  static inline bool debug_pagealloc_enabled(void)
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index fd5c95ff9251..2f75dd0d0d81 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -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);
>         }
> diff --git a/mm/dmapool.c b/mm/dmapool.c
> index 76a160083506..493d151067cb 100644
> --- a/mm/dmapool.c
> +++ b/mm/dmapool.c
> @@ -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;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3b13d3914176..14ded6620aa0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -135,6 +135,48 @@ 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
> @@ -1089,6 +1131,14 @@ 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 +1191,8 @@ static __always_inline bool free_pages_prepare(struct page *page,
>         }
>         arch_free_page(page, order);
>         kernel_poison_pages(page, 1 << order, 0);
> +       if (want_init_on_free())
> +               kernel_init_free_pages(page, 1 << order);
>         if (debug_pagealloc_enabled())
>                 kernel_map_pages(page, 1 << order, 0);
>
> @@ -2019,8 +2071,8 @@ 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
> @@ -2074,13 +2126,10 @@ 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 2915d912e89a..d42eb11f8f50 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1853,6 +1853,14 @@ 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;
>
> @@ -3293,7 +3301,7 @@ 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);
> @@ -3350,7 +3358,7 @@ 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);
> @@ -3471,6 +3479,8 @@ 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);
>
> @@ -3558,7 +3568,7 @@ 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..24ae887359b8 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -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 */
> diff --git a/mm/slob.c b/mm/slob.c
> index 84aefd9b91ee..1b565ee7f479 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -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;
> +}
> +
>  /*
>   * slob_page_alloc() - Allocate a slob block within a given slob_page sp.
>   * @sp: Page to look in.
> @@ -353,8 +366,6 @@ 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;
>  }
>
> @@ -389,6 +400,9 @@ 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;
> @@ -484,6 +498,8 @@ __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;
>  }
>
> @@ -582,6 +598,8 @@ 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;
> diff --git a/mm/slub.c b/mm/slub.c
> index cd04dbd2b5d0..5fcb3f71cf84 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1424,6 +1424,19 @@ 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.
> @@ -1433,9 +1446,7 @@ 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 +2752,14 @@ 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;
Ugh, I forgot to s/0/NULL/ here.
There also must be a check for object being nonnull itself.
I'll send a follow-up.
>
> -       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 +3180,7 @@ 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 75b1c950b49f..9ceb90c875bc 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1602,7 +1602,7 @@ static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,
>                 sk = kmem_cachffffff80081dd078e_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 0a1d4ca314f4..87883e3e3c2a 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -159,6 +159,20 @@ 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"
> +       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"
> +       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
> --
> 2.21.0.1020.gf2820cf01a-goog
>


-- 
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

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