[PATCH 5.15 011/124] mm, kfence: support kmem_dump_obj() for KFENCE objects

Greg Kroah-Hartman
2022-04-26T09:03:17Z

From: Marco Elver <elver@google.com>

commit 2dfe63e61cc31ee59ce951672b0850b5229cd5b0 upstream.

Calling kmem_obj_info() via kmem_dump_obj() on KFENCE objects has been
producing garbage data due to the object not actually being maintained
by SLAB or SLUB.

Fix this by implementing __kfence_obj_info() that copies relevant
information to struct kmem_obj_info when the object was allocated by
KFENCE; this is called by a common kmem_obj_info(), which also calls the
slab/slub/slob specific variant now called __kmem_obj_info().

For completeness, kmem_dump_obj() now displays if the object was
allocated by KFENCE.

Link: https://lore.kernel.org/all/20220323090520.GG16885@xsang-OptiPlex-9020/
Link: https://lkml.kernel.org/r/20220406131558.3558585-1-elver@google.com
Fixes: b89fb5ef0ce6 ("mm, kfence: insert KFENCE hooks for SLUB")
Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB")
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz> [slab]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/kfence.h | 24 ++++++++++++++++++++++++
mm/kfence/core.c | 21 ---------------------
mm/kfence/kfence.h | 21 +++++++++++++++++++++
mm/kfence/report.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
mm/slab.c | 2 +-
mm/slab.h | 2 +-
mm/slab_common.c | 9 +++++++++
mm/slob.c | 2 +-
mm/slub.c | 2 +-
9 files changed, 105 insertions(+), 25 deletions(-)

--- a/include/linux/kfence.h
+++ b/include/linux/kfence.h
@@ -202,6 +202,22 @@ static __always_inline __must_check bool
*/
bool __must_check kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs);

+#ifdef CONFIG_PRINTK
+struct kmem_obj_info;
+/**
+ * __kfence_obj_info() - fill kmem_obj_info struct
+ * @kpp: kmem_obj_info to be filled
+ * @object: the object
+ *
+ * Return:
+ * * false - not a KFENCE object
+ * * true - a KFENCE object, filled @kpp
+ *
+ * Copies information to @kpp for KFENCE objects.
+ */
+bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page);
+#endif
+
#else /* CONFIG_KFENCE */

static inline bool is_kfence_address(const void *addr) { return false; }
@@ -219,6 +235,14 @@ static inline bool __must_check kfence_h
return false;
}

+#ifdef CONFIG_PRINTK
+struct kmem_obj_info;
+static inline bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+{
+ return false;
+}
+#endif
+
#endif

#endif /* _LINUX_KFENCE_H */
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -221,27 +221,6 @@ static bool kfence_unprotect(unsigned lo
return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false));
}

-static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
-{
- long index;
-
- /* The checks do not affect performance; only called from slow-paths. */
-
- if (!is_kfence_address((void *)addr))
- return NULL;
-
- /*
- * May be an invalid index if called with an address at the edge of
- * __kfence_pool, in which case we would report an "invalid access"
- * error.
- */
- index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
- if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
- return NULL;
-
- return &kfence_metadata[index];
-}
-
static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta)
{
unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2;
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -93,6 +93,27 @@ struct kfence_metadata {

extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];

+static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
+{
+ long index;
+
+ /* The checks do not affect performance; only called from slow-paths. */
+
+ if (!is_kfence_address((void *)addr))
+ return NULL;
+
+ /*
+ * May be an invalid index if called with an address at the edge of
+ * __kfence_pool, in which case we would report an "invalid access"
+ * error.
+ */
+ index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
+ if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
+ return NULL;
+
+ return &kfence_metadata[index];
+}
+
/* KFENCE error types for report generation. */
enum kfence_error_type {
KFENCE_ERROR_OOB, /* Detected a out-of-bounds access. */
--- a/mm/kfence/report.c
+++ b/mm/kfence/report.c
@@ -273,3 +273,50 @@ void kfence_report_error(unsigned long a
/* We encountered a memory safety error, taint the kernel! */
add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
}
+
+#ifdef CONFIG_PRINTK
+static void kfence_to_kp_stack(const struct kfence_track *track, void **kp_stack)
+{
+ int i, j;
+
+ i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
+ for (j = 0; i < track->num_stack_entries && j < KS_ADDRS_COUNT; ++i, ++j)
+ kp_stack[j] = (void *)track->stack_entries[i];
+ if (j < KS_ADDRS_COUNT)
+ kp_stack[j] = NULL;
+}
+
+bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+{
+ struct kfence_metadata *meta = addr_to_metadata((unsigned long)object);
+ unsigned long flags;
+
+ if (!meta)
+ return false;
+
+ /*
+ * If state is UNUSED at least show the pointer requested; the rest
+ * would be garbage data.
+ */
+ kpp->kp_ptr = object;
+
+ /* Requesting info an a never-used object is almost certainly a bug. */
+ if (WARN_ON(meta->state == KFENCE_OBJECT_UNUSED))
+ return true;
+
+ raw_spin_lock_irqsave(&meta->lock, flags);
+
+ kpp->kp_page = page;
+ kpp->kp_slab_cache = meta->cache;
+ kpp->kp_objp = (void *)meta->addr;
+ kfence_to_kp_stack(&meta->alloc_track, kpp->kp_stack);
+ if (meta->state == KFENCE_OBJECT_FREED)
+ kfence_to_kp_stack(&meta->free_track, kpp->kp_free_stack);
+ /* get_stack_skipnr() ensures the first entry is outside allocator. */
+ kpp->kp_ret = kpp->kp_stack[0];
+
+ raw_spin_unlock_irqrestore(&meta->lock, flags);
+
+ return true;
+}
+#endif
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3658,7 +3658,7 @@ EXPORT_SYMBOL(__kmalloc_node_track_calle
#endif /* CONFIG_NUMA */

#ifdef CONFIG_PRINTK
-void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
{
struct kmem_cache *cachep;
unsigned int objnr;
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -643,7 +643,7 @@ struct kmem_obj_info {
void *kp_stack[KS_ADDRS_COUNT];
void *kp_free_stack[KS_ADDRS_COUNT];
};
-void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page);
+void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page);
#endif

#endif /* MM_SLAB_H */
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -568,6 +568,13 @@ bool kmem_valid_obj(void *object)
}
EXPORT_SYMBOL_GPL(kmem_valid_obj);

+static void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+{
+ if (__kfence_obj_info(kpp, object, page))
+ return;
+ __kmem_obj_info(kpp, object, page);
+}
+
/**
* kmem_dump_obj - Print available slab provenance information
* @object: slab object for which to find provenance information.
@@ -603,6 +610,8 @@ void kmem_dump_obj(void *object)
pr_cont(" slab%s %s", cp, kp.kp_slab_cache->name);
else
pr_cont(" slab%s", cp);
+ if (is_kfence_address(object))
+ pr_cont(" (kfence)");
if (kp.kp_objp)
pr_cont(" start %px", kp.kp_objp);
if (kp.kp_data_offset)
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -462,7 +462,7 @@ out:
}

#ifdef CONFIG_PRINTK
-void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
{
kpp->kp_ptr = object;
kpp->kp_page = page;
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4299,7 +4299,7 @@ int __kmem_cache_shutdown(struct kmem_ca
}

#ifdef CONFIG_PRINTK
-void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
+void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
{
void *base;
int __maybe_unused i;