[PATCH v4 04/11] mm, kfence: insert KFENCE hooks for SLAB

Marco Elver
2020-09-29T13:41:35Z

From: Alexander Potapenko <glider@google.com>

Inserts KFENCE hooks into the SLAB allocator.

To pass the originally requested size to KFENCE, add an argument
'orig_size' to slab_alloc*(). The additional argument is required to
preserve the requested original size for kmalloc() allocations, which
uses size classes (e.g. an allocation of 272 bytes will return an object
of size 512). Therefore, kmem_cache::size does not represent the
kmalloc-caller's requested size, and we must introduce the argument
'orig_size' to propagate the originally requested size to KFENCE.

Without the originally requested size, we would not be able to detect
out-of-bounds accesses for objects placed at the end of a KFENCE object
page if that object is not equal to the kmalloc-size class it was
bucketed into.

When KFENCE is disabled, there is no additional overhead, since
slab_alloc*() functions are __always_inline.

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Co-developed-by: Marco Elver <elver@google.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
---
v3:
* Rewrite patch description to clarify need for 'orig_size'
[reported by Christopher Lameter].
---
mm/slab.c | 46 ++++++++++++++++++++++++++++++++++------------
mm/slab_common.c | 6 +++++-
2 files changed, 39 insertions(+), 13 deletions(-)

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.
--
2.28.0.709.gb0816b6eb0-goog