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Date: Fri, 12 Apr 2019 14:45:01 +0200
From: Alexander Potapenko <glider@...gle.com>
To: akpm@...ux-foundation.org
Cc: linux-security-module@...r.kernel.org, linux-mm@...ck.org,
ndesaulniers@...gle.com, kcc@...gle.com, dvyukov@...gle.com,
keescook@...omium.org, sspatil@...roid.com, labbott@...hat.com,
kernel-hardening@...ts.openwall.com
Subject: [PATCH] mm: security: introduce CONFIG_INIT_HEAP_ALL
This config option adds the possibility to initialize newly allocated
pages and heap objects with zeroes. This is needed to prevent possible
information leaks and make the control-flow bugs that depend on
uninitialized values more deterministic.
Initialization is done at allocation time at the places where checks for
__GFP_ZERO are performed. We don't initialize slab caches with
constructors or SLAB_TYPESAFE_BY_RCU to preserve their semantics.
For kernel testing purposes filling allocations with a nonzero pattern
would be more suitable, but may require platform-specific code. To have
a simple baseline we've decided to start with zero-initialization.
No performance optimizations are done at the moment to reduce double
initialization of memory regions.
Signed-off-by: Alexander Potapenko <glider@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
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: Kees Cook <keescook@...omium.org>
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
---
This patch applies on top of the "Refactor memory initialization
hardening" patch series by Kees Cook: https://lkml.org/lkml/2019/4/10/748
---
drivers/infiniband/core/uverbs_ioctl.c | 2 +-
include/linux/gfp.h | 8 ++++++++
kernel/kexec_core.c | 2 +-
mm/dmapool.c | 2 +-
mm/page_alloc.c | 2 +-
mm/slab.c | 6 +++---
mm/slab.h | 10 ++++++++++
mm/slob.c | 2 +-
mm/slub.c | 4 ++--
net/core/sock.c | 2 +-
security/Kconfig.hardening | 10 ++++++++++
11 files changed, 39 insertions(+), 11 deletions(-)
diff --git a/drivers/infiniband/core/uverbs_ioctl.c b/drivers/infiniband/core/uverbs_ioctl.c
index e1379949e663..34937cecac62 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 (GFP_WANT_INIT(flags))
memset(res, 0, size);
return res;
}
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index fdab7de7490d..4f49a6a13f6f 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -213,6 +213,14 @@ struct vm_area_struct;
#define __GFP_COMP ((__force gfp_t)___GFP_COMP)
#define __GFP_ZERO ((__force gfp_t)___GFP_ZERO)
+#ifdef CONFIG_INIT_HEAP_ALL
+#define GFP_WANT_INIT(flags) (1)
+#define GFP_INIT_ALWAYS_ON (1)
+#else
+#define GFP_WANT_INIT(flags) (unlikely((flags) & __GFP_ZERO))
+#define GFP_INIT_ALWAYS_ON (0)
+#endif
+
/* Disable lockdep for GFP context tracking */
#define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index d7140447be75..1ad0097695a1 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 (GFP_WANT_INIT(gfp_mask))
for (i = 0; i < count; i++)
clear_highpage(pages + i);
}
diff --git a/mm/dmapool.c b/mm/dmapool.c
index 76a160083506..d40d62145ca3 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 (GFP_WANT_INIT(mem_flags))
memset(retval, 0, pool->size);
return retval;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d96ca5bc555b..ceddc4eeaff4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2014,7 +2014,7 @@ 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() && GFP_WANT_INIT(gfp_flags))
for (i = 0; i < (1 << order); i++)
clear_highpage(page + i);
diff --git a/mm/slab.c b/mm/slab.c
index 47a380a486ee..848e47658667 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3331,7 +3331,7 @@ 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 (SLAB_WANT_INIT(cachep, flags) && ptr)
memset(ptr, 0, cachep->object_size);
slab_post_alloc_hook(cachep, flags, 1, &ptr);
@@ -3388,7 +3388,7 @@ 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 (SLAB_WANT_INIT(cachep, flags) && objp)
memset(objp, 0, cachep->object_size);
slab_post_alloc_hook(cachep, flags, 1, &objp);
@@ -3596,7 +3596,7 @@ 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 (SLAB_WANT_INIT(s, flags))
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..4bb10af0031b 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -167,6 +167,16 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
SLAB_TEMPORARY | \
SLAB_ACCOUNT)
+/*
+ * Do we need to initialize this allocation?
+ * Always true for __GFP_ZERO, CONFIG_INIT_HEAP_ALL enforces initialization
+ * of caches without constructors and RCU.
+ */
+#define SLAB_WANT_INIT(cache, gfp_flags) \
+ ((GFP_INIT_ALWAYS_ON && !(cache)->ctor && \
+ !((cache)->flags & SLAB_TYPESAFE_BY_RCU)) || \
+ (gfp_flags & __GFP_ZERO))
+
bool __kmem_cache_empty(struct kmem_cache *);
int __kmem_cache_shutdown(struct kmem_cache *);
void __kmem_cache_release(struct kmem_cache *);
diff --git a/mm/slob.c b/mm/slob.c
index 307c2c9feb44..0c402e819cf7 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -330,7 +330,7 @@ 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))
+ if (GFP_WANT_INIT(gfp))
memset(b, 0, size);
return b;
}
diff --git a/mm/slub.c b/mm/slub.c
index d30ede89f4a6..686ab9d49ced 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2750,7 +2750,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
stat(s, ALLOC_FASTPATH);
}
- if (unlikely(gfpflags & __GFP_ZERO) && object)
+ if (SLAB_WANT_INIT(s, gfpflags) && object)
memset(object, 0, s->object_size);
slab_post_alloc_hook(s, gfpflags, 1, &object);
@@ -3172,7 +3172,7 @@ 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 (SLAB_WANT_INIT(s, flags)) {
int j;
for (j = 0; j < i; j++)
diff --git a/net/core/sock.c b/net/core/sock.c
index 782343bb925b..51b13d7fd82f 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -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 (GFP_WANT_INIT(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 d744e20140b4..cb7d7dfb506f 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -93,6 +93,16 @@ choice
endchoice
+config INIT_HEAP_ALL
+ bool "Initialize kernel heap allocations"
+ default n
+ help
+ Enforce initialization of pages allocated from page allocator
+ and objects returned by kmalloc and friends.
+ Allocated memory is initialized with zeroes, preventing possible
+ information leaks and making the control-flow bugs that depend
+ on uninitialized values more deterministic.
+
config GCC_PLUGIN_STRUCTLEAK_VERBOSE
bool "Report forcefully initialized variables"
depends on GCC_PLUGIN_STRUCTLEAK
--
2.21.0.392.gf8f6787159e-goog
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