mm/slab: expand CONFIG_SLAB_FREELIST_HARDENED to include SLAB

Patch series "mm: Expand CONFIG_SLAB_FREELIST_HARDENED to include SLAB"

In reviewing Vlastimil Babka's latest slub debug series, I realized[1]
that several checks under CONFIG_SLAB_FREELIST_HARDENED weren't being
applied to SLAB.  Fix this by expanding the Kconfig coverage, and adding a
simple double-free test for SLAB.

This patch (of 2):

Include SLAB caches when performing kmem_cache pointer verification.  A
defense against such corruption[1] should be applied to all the
allocators.  With this added, the "SLAB_FREE_CROSS" and "SLAB_FREE_PAGE"
LKDTM tests now pass on SLAB:

  lkdtm: Performing direct entry SLAB_FREE_CROSS
  lkdtm: Attempting cross-cache slab free ...
  ------------[ cut here ]------------
  cache_from_obj: Wrong slab cache. lkdtm-heap-b but object is from lkdtm-heap-a
  WARNING: CPU: 2 PID: 2195 at mm/slab.h:530 kmem_cache_free+0x8d/0x1d0
  ...
  lkdtm: Performing direct entry SLAB_FREE_PAGE
  lkdtm: Attempting non-Slab slab free ...
  ------------[ cut here ]------------
  virt_to_cache: Object is not a Slab page!
  WARNING: CPU: 1 PID: 2202 at mm/slab.h:489 kmem_cache_free+0x196/0x1d0

Additionally clean up neighboring Kconfig entries for clarity,
readability, and redundant option removal.

[1] https://github.com/ThomasKing2014/slides/raw/master/Building%20universal%20Android%20rooting%20with%20a%20type%20confusion%20vulnerability.pdf

Fixes: 598a0717 ("mm/slab: validate cache membership under freelist hardening")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Garrett <mjg59@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: Vinayak Menon <vinmenon@codeaurora.org>
Link: http://lkml.kernel.org/r/20200625215548.389774-1-keescook@chromium.org
Link: http://lkml.kernel.org/r/20200625215548.389774-2-keescook@chromium.orgSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

init/Kconfig

@@ -1913,9 +1913,8 @@ config SLAB_MERGE_DEFAULT
 	  command line.
 
 config SLAB_FREELIST_RANDOM
-	default n
+	bool "Randomize slab freelist"
 	depends on SLAB || SLUB
-	bool "SLAB freelist randomization"
 	help
 	  Randomizes the freelist order used on creating new pages. This
 	  security feature reduces the predictability of the kernel slab
@@ -1923,12 +1922,14 @@ config SLAB_FREELIST_RANDOM
 
 config SLAB_FREELIST_HARDENED
 	bool "Harden slab freelist metadata"
-	depends on SLUB
+	depends on SLAB || SLUB
 	help
 	  Many kernel heap attacks try to target slab cache metadata and
 	  other infrastructure. This options makes minor performance
 	  sacrifices to harden the kernel slab allocator against common
-	  freelist exploit methods.
+	  freelist exploit methods. Some slab implementations have more
+	  sanity-checking than others. This option is most effective with
+	  CONFIG_SLUB.
 
 config SHUFFLE_PAGE_ALLOCATOR
 	bool "Page allocator randomization"