kernel: Activate CONFIG_SLAB_FREELIST_HARDENED

This activates some extra checks in SLAB or SLUB to make it harder to
execute kernel heap exploits. This adds a minor performance
degradation which I haven't measured-.

Many mainstream Linux distributions also activate this option.

Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/generic/config-5.10

@@ -5463,7 +5463,7 @@ CONFIG_SIGNALFD=y
 # CONFIG_SKY2_DEBUG is not set
 # CONFIG_SLAB is not set
 CONFIG_SLABINFO=y
-# CONFIG_SLAB_FREELIST_HARDENED is not set
+CONFIG_SLAB_FREELIST_HARDENED=y
 # CONFIG_SLAB_FREELIST_RANDOM is not set
 CONFIG_SLAB_MERGE_DEFAULT=y
 # CONFIG_SLHC is not set

target/linux/generic/config-5.15

@@ -5753,7 +5753,7 @@ CONFIG_SIGNALFD=y
 # CONFIG_SKY2_DEBUG is not set
 # CONFIG_SLAB is not set
 CONFIG_SLABINFO=y
-# CONFIG_SLAB_FREELIST_HARDENED is not set
+CONFIG_SLAB_FREELIST_HARDENED=y
 # CONFIG_SLAB_FREELIST_RANDOM is not set
 CONFIG_SLAB_MERGE_DEFAULT=y
 # CONFIG_SLHC is not set