[kernel-hardening] [RFC][PATCH 4/7] slob: Add support for sanitization

Laura Abbott
2015-12-22T03:40:38Z

The SLOB allocator does not clear objects on free. This is a security
risk since sensitive data may exist long past its expected life
span. Add support for clearing objects on free.

All credit for the original work should be given to Brad Spengler and
the PaX Team.

Signed-off-by: Laura Abbott <laura@labbott.name>
---
mm/slob.c | 25 +++++++++++++++++++------
1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/mm/slob.c b/mm/slob.c
index 17e8f8c..37a4ecb 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -334,10 +334,21 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
return b;
}

+static void slob_sanitize(struct kmem_cache *c, slob_t *b, int size)
+{
+#ifdef CONFIG_SLAB_MEMORY_SANITIZE
+ if (c && (c->flags & SLAB_NO_SANITIZE))
+ return;
+
+ if (sanitize_slab)
+ memset(b, SLAB_MEMORY_SANITIZE_VALUE, size);
+#endif
+}
+
/*
* slob_free: entry point into the slob allocator.
*/
-static void slob_free(void *block, int size)
+static void slob_free(struct kmem_cache *c, void *block, int size)
{
struct page *sp;
slob_t *prev, *next, *b = (slob_t *)block;
@@ -365,6 +376,8 @@ static void slob_free(void *block, int size)
return;
}

+ slob_sanitize(c, block, size);
+
if (!slob_page_free(sp)) {
/* This slob page is about to become partially free. Easy! */
sp->units = units;
@@ -495,7 +508,7 @@ void kfree(const void *block)
if (PageSlab(sp)) {
int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
unsigned int *m = (unsigned int *)(block - align);
- slob_free(m, *m + align);
+ slob_free(NULL, m, *m + align);
} else
__free_pages(sp, compound_order(sp));
}
@@ -579,10 +592,10 @@ void *kmem_cache_alloc_node(struct kmem_cache *cachep, gfp_t gfp, int node)
EXPORT_SYMBOL(kmem_cache_alloc_node);
#endif

-static void __kmem_cache_free(void *b, int size)
+static void __kmem_cache_free(struct kmem_cache *c, void *b, int size)
{
if (size < PAGE_SIZE)
- slob_free(b, size);
+ slob_free(c, b, size);
else
slob_free_pages(b, get_order(size));
}
@@ -592,7 +605,7 @@ static void kmem_rcu_free(struct rcu_head *head)
struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));

- __kmem_cache_free(b, slob_rcu->size);
+ __kmem_cache_free(NULL, b, slob_rcu->size);
}

void kmem_cache_free(struct kmem_cache *c, void *b)
@@ -604,7 +617,7 @@ void kmem_cache_free(struct kmem_cache *c, void *b)
slob_rcu->size = c->size;
call_rcu(&slob_rcu->head, kmem_rcu_free);
} else {
- __kmem_cache_free(b, c->size);
+ __kmem_cache_free(NULL, b, c->size);
}

trace_kmem_cache_free(_RET_IP_, b);
--
2.5.0