[PATCH v2 1/2] mm: Expand CONFIG_SLAB_FREELIST_HARDENED to include SLAB

[Kees Cook]

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: 598a0717a816 ("mm/slab: validate cache membership under freelist hardening")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 init/Kconfig | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index a46aa8f3174d..7542d28c6f61 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1885,9 +1885,8 @@ 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
@@ -1895,12 +1894,14 @@ 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"
-- 
2.25.1