mm/slab: Introduce kmem_buckets_create() and family

Dedicated caches are available for fixed size allocations via
kmem_cache_alloc(), but for dynamically sized allocations there is only
the global kmalloc API's set of buckets available. This means it isn't
possible to separate specific sets of dynamically sized allocations into
a separate collection of caches.

This leads to a use-after-free exploitation weakness in the Linux
kernel since many heap memory spraying/grooming attacks depend on using
userspace-controllable dynamically sized allocations to collide with
fixed size allocations that end up in same cache.

While CONFIG_RANDOM_KMALLOC_CACHES provides a probabilistic defense
against these kinds of "type confusion" attacks, including for fixed
same-size heap objects, we can create a complementary deterministic
defense for dynamically sized allocations that are directly user
controlled. Addressing these cases is limited in scope, so isolating these
kinds of interfaces will not become an unbounded game of whack-a-mole. For
example, many pass through memdup_user(), making isolation there very
effective.

In order to isolate user-controllable dynamically-sized
allocations from the common system kmalloc allocations, introduce
kmem_buckets_create(), which behaves like kmem_cache_create(). Introduce
kmem_buckets_alloc(), which behaves like kmem_cache_alloc(). Introduce
kmem_buckets_alloc_track_caller() for where caller tracking is
needed. Introduce kmem_buckets_valloc() for cases where vmalloc fallback
is needed. Note that these caches are specifically flagged with
SLAB_NO_MERGE, since merging would defeat the entire purpose of the
mitigation.

This can also be used in the future to extend allocation profiling's use
of code tagging to implement per-caller allocation cache isolation[1]
even for dynamic allocations.

Memory allocation pinning[2] is still needed to plug the Use-After-Free
cross-allocator weakness (where attackers can arrange to free an
entire slab page and have it reallocated to a different cache),
but that is an existing and separate issue which is complementary
to this improvement. Development continues for that feature via the
SLAB_VIRTUAL[3] series (which could also provide guard pages -- another
complementary improvement).

Link: https://lore.kernel.org/lkml/202402211449.401382D2AF@keescook [1]
Link: https://googleprojectzero.blogspot.com/2021/10/how-simple-linux-kernel-memory.html [2]
Link: https://lore.kernel.org/lkml/20230915105933.495735-1-matteorizzo@google.com/ [3]
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 837005314f96..d99afce36098 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -549,6 +549,10 @@ void *kmem_cache_alloc_lru_noprof(struct kmem_cache *s, struct list_lru *lru,
 
 void kmem_cache_free(struct kmem_cache *s, void *objp);
 
+kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags,
+				  unsigned int useroffset, unsigned int usersize,
+				  void (*ctor)(void *));
+
 /*
  * Bulk allocation and freeing operations. These are accelerated in an
  * allocator specific way to avoid taking locks repeatedly or building
@@ -682,6 +686,12 @@ static __always_inline __alloc_size(1) void *kmalloc_noprof(size_t size, gfp_t f
 }
 #define kmalloc(...)				alloc_hooks(kmalloc_noprof(__VA_ARGS__))
 
+#define kmem_buckets_alloc(_b, _size, _flags)	\
+	alloc_hooks(__kmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE))
+
+#define kmem_buckets_alloc_track_caller(_b, _size, _flags)	\
+	alloc_hooks(__kmalloc_node_track_caller_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE, _RET_IP_))
+
 static __always_inline __alloc_size(1) void *kmalloc_node_noprof(size_t size, gfp_t flags, int node)
 {
 	if (__builtin_constant_p(size) && size) {
@@ -809,6 +819,8 @@ void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node)
 #define kvzalloc(_size, _flags)			kvmalloc(_size, (_flags)|__GFP_ZERO)
 
 #define kvzalloc_node(_size, _flags, _node)	kvmalloc_node(_size, (_flags)|__GFP_ZERO, _node)
+#define kmem_buckets_valloc(_b, _size, _flags)	\
+	alloc_hooks(__kvmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE))
 
 static inline __alloc_size(1, 2) void *
 kvmalloc_array_node_noprof(size_t n, size_t size, gfp_t flags, int node)