[v2,04/10] mm, kfence: insert KFENCE hooks for SLAB

Commit Message

Marco Elver Sept. 15, 2020, 1:20 p.m. UTC

From: Alexander Potapenko <[e-mail]>

Inserts KFENCE hooks into the SLAB allocator.

We note the addition of the 'orig_size' argument to slab_alloc*()
functions, to be able to pass the originally requested size to KFENCE.
When KFENCE is disabled, there is no additional overhead, since these
functions are __always_inline.

Co-developed-by: Marco Elver <[e-mail]>
Signed-off-by: Marco Elver <[e-mail]>
Signed-off-by: Alexander Potapenko <[e-mail]>
---
 mm/slab.c        | 46 ++++++++++++++++++++++++++++++++++------------
 mm/slab_common.c |  6 +++++-
 2 files changed, 39 insertions(+), 13 deletions(-)

Comments

Christoph Lameter (Ampere) Sept. 17, 2020, 9:37 a.m. UTC | #1

On Tue, 15 Sep 2020, Marco Elver wrote:

> @@ -3206,7 +3207,7 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
>  }
>
>  static __always_inline void *
> -slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
> +slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, size_t orig_size,
>  		   unsigned long caller)
>  {

The size of the object is available via a field in kmem_cache. And a
pointer to the current kmem_cache is already passed to the function. Why
is there a need to add an additional parameter?

Alexander Potapenko Sept. 17, 2020, 9:47 a.m. UTC | #2

> >  static __always_inline void *
> > -slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
> > +slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, size_t orig_size,
> >                  unsigned long caller)
> >  {
>
> The size of the object is available via a field in kmem_cache. And a
> pointer to the current kmem_cache is already passed to the function. Why
> is there a need to add an additional parameter?

That's because we want to do our best detecting bugs on
kmalloc-allocated objects.
kmalloc is using size classes, so e.g. when allocating 272 bytes the
object will be padded to 512.
As a result, placing that object at the end of the page won't really
help to detect out-of-bound accesses that are off by less than 270
bytes.

We probably need to better clarify this in the patch description.

Patch

diff --git a/mm/slab.c b/mm/slab.c
index 3160dff6fd76..30aba06ae02b 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -100,6 +100,7 @@ 
 #include	<linux/seq_file.h>
 #include	<linux/notifier.h>
 #include	<linux/kallsyms.h>
+#include	<linux/kfence.h>
 #include	<linux/cpu.h>
 #include	<linux/sysctl.h>
 #include	<linux/module.h>
@@ -3206,7 +3207,7 @@  static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
 }
 
 static __always_inline void *
-slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
+slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, size_t orig_size,
 		   unsigned long caller)
 {
 	unsigned long save_flags;
@@ -3219,6 +3220,10 @@  slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
 	if (unlikely(!cachep))
 		return NULL;
 
+	ptr = kfence_alloc(cachep, orig_size, flags);
+	if (unlikely(ptr))
+		goto out_hooks;
+
 	cache_alloc_debugcheck_before(cachep, flags);
 	local_irq_save(save_flags);
 
@@ -3251,6 +3256,7 @@  slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
 	if (unlikely(slab_want_init_on_alloc(flags, cachep)) && ptr)
 		memset(ptr, 0, cachep->object_size);
 
+out_hooks:
 	slab_post_alloc_hook(cachep, objcg, flags, 1, &ptr);
 	return ptr;
 }
@@ -3288,7 +3294,7 @@  __do_cache_alloc(struct kmem_cache *cachep, gfp_t flags)
 #endif /* CONFIG_NUMA */
 
 static __always_inline void *
-slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller)
+slab_alloc(struct kmem_cache *cachep, gfp_t flags, size_t orig_size, unsigned long caller)
 {
 	unsigned long save_flags;
 	void *objp;
@@ -3299,6 +3305,10 @@  slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller)
 	if (unlikely(!cachep))
 		return NULL;
 
+	objp = kfence_alloc(cachep, orig_size, flags);
+	if (unlikely(objp))
+		goto leave;
+
 	cache_alloc_debugcheck_before(cachep, flags);
 	local_irq_save(save_flags);
 	objp = __do_cache_alloc(cachep, flags);
@@ -3309,6 +3319,7 @@  slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller)
 	if (unlikely(slab_want_init_on_alloc(flags, cachep)) && objp)
 		memset(objp, 0, cachep->object_size);
 
+leave:
 	slab_post_alloc_hook(cachep, objcg, flags, 1, &objp);
 	return objp;
 }
@@ -3414,6 +3425,11 @@  static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac)
 static __always_inline void __cache_free(struct kmem_cache *cachep, void *objp,
 					 unsigned long caller)
 {
+	if (kfence_free(objp)) {
+		kmemleak_free_recursive(objp, cachep->flags);
+		return;
+	}
+
 	/* Put the object into the quarantine, don't touch it for now. */
 	if (kasan_slab_free(cachep, objp, _RET_IP_))
 		return;
@@ -3479,7 +3495,7 @@  void ___cache_free(struct kmem_cache *cachep, void *objp,
  */
 void *kmem_cache_alloc(struct kmem_cache *cachep, gfp_t flags)
 {
-	void *ret = slab_alloc(cachep, flags, _RET_IP_);
+	void *ret = slab_alloc(cachep, flags, cachep->object_size, _RET_IP_);
 
 	trace_kmem_cache_alloc(_RET_IP_, ret,
 			       cachep->object_size, cachep->size, flags);
@@ -3512,7 +3528,7 @@  int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 
 	local_irq_disable();
 	for (i = 0; i < size; i++) {
-		void *objp = __do_cache_alloc(s, flags);
+		void *objp = kfence_alloc(s, s->object_size, flags) ?: __do_cache_alloc(s, flags);
 
 		if (unlikely(!objp))
 			goto error;
@@ -3545,7 +3561,7 @@  kmem_cache_alloc_trace(struct kmem_cache *cachep, gfp_t flags, size_t size)
 {
 	void *ret;
 
-	ret = slab_alloc(cachep, flags, _RET_IP_);
+	ret = slab_alloc(cachep, flags, size, _RET_IP_);
 
 	ret = kasan_kmalloc(cachep, ret, size, flags);
 	trace_kmalloc(_RET_IP_, ret,
@@ -3571,7 +3587,7 @@  EXPORT_SYMBOL(kmem_cache_alloc_trace);
  */
 void *kmem_cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid)
 {
-	void *ret = slab_alloc_node(cachep, flags, nodeid, _RET_IP_);
+	void *ret = slab_alloc_node(cachep, flags, nodeid, cachep->object_size, _RET_IP_);
 
 	trace_kmem_cache_alloc_node(_RET_IP_, ret,
 				    cachep->object_size, cachep->size,
@@ -3589,7 +3605,7 @@  void *kmem_cache_alloc_node_trace(struct kmem_cache *cachep,
 {
 	void *ret;
 
-	ret = slab_alloc_node(cachep, flags, nodeid, _RET_IP_);
+	ret = slab_alloc_node(cachep, flags, nodeid, size, _RET_IP_);
 
 	ret = kasan_kmalloc(cachep, ret, size, flags);
 	trace_kmalloc_node(_RET_IP_, ret,
@@ -3650,7 +3666,7 @@  static __always_inline void *__do_kmalloc(size_t size, gfp_t flags,
 	cachep = kmalloc_slab(size, flags);
 	if (unlikely(ZERO_OR_NULL_PTR(cachep)))
 		return cachep;
-	ret = slab_alloc(cachep, flags, caller);
+	ret = slab_alloc(cachep, flags, size, caller);
 
 	ret = kasan_kmalloc(cachep, ret, size, flags);
 	trace_kmalloc(caller, ret,
@@ -4138,18 +4154,24 @@  void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 			 bool to_user)
 {
 	struct kmem_cache *cachep;
-	unsigned int objnr;
+	unsigned int objnr = 0;
 	unsigned long offset;
+	bool is_kfence = is_kfence_address(ptr);
 
 	ptr = kasan_reset_tag(ptr);
 
 	/* Find and validate object. */
 	cachep = page->slab_cache;
-	objnr = obj_to_index(cachep, page, (void *)ptr);
-	BUG_ON(objnr >= cachep->num);
+	if (!is_kfence) {
+		objnr = obj_to_index(cachep, page, (void *)ptr);
+		BUG_ON(objnr >= cachep->num);
+	}
 
 	/* Find offset within object. */
-	offset = ptr - index_to_obj(cachep, page, objnr) - obj_offset(cachep);
+	if (is_kfence_address(ptr))
+		offset = ptr - kfence_object_start(ptr);
+	else
+		offset = ptr - index_to_obj(cachep, page, objnr) - obj_offset(cachep);
 
 	/* Allow address range falling entirely within usercopy region. */
 	if (offset >= cachep->useroffset &&
diff --git a/mm/slab_common.c b/mm/slab_common.c
index f9ccd5dc13f3..6e35e273681a 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -12,6 +12,7 @@ 
 #include <linux/memory.h>
 #include <linux/cache.h>
 #include <linux/compiler.h>
+#include <linux/kfence.h>
 #include <linux/module.h>
 #include <linux/cpu.h>
 #include <linux/uaccess.h>
@@ -448,6 +449,9 @@  static int shutdown_cache(struct kmem_cache *s)
 	/* free asan quarantined objects */
 	kasan_cache_shutdown(s);
 
+	if (!kfence_shutdown_cache(s))
+		return -EBUSY;
+
 	if (__kmem_cache_shutdown(s) != 0)
 		return -EBUSY;
 
@@ -1171,7 +1175,7 @@  size_t ksize(const void *objp)
 	if (unlikely(ZERO_OR_NULL_PTR(objp)) || !__kasan_check_read(objp, 1))
 		return 0;
 
-	size = __ksize(objp);
+	size = kfence_ksize(objp) ?: __ksize(objp);
 	/*
 	 * We assume that ksize callers could use whole allocated area,
 	 * so we need to unpoison this area.