mm: security: Move hardened usercopy under 'Kernel hardening options'

There is a submenu for 'Kernel hardening options' under "Security".
Move HARDENED_USERCOPY under the hardening options as it is clearly
related.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250123221115.19722-2-mgorman@techsingularity.net
Signed-off-by: Kees Cook <kees@kernel.org>

security/Kconfig

@@ -164,18 +164,6 @@ config LSM_MMAP_MIN_ADDR
 	  this low address space will need the permission specific to the
 	  systems running LSM.
 
-config HARDENED_USERCOPY
-	bool "Harden memory copies between kernel and userspace"
-	imply STRICT_DEVMEM
-	help
-	  This option checks for obviously wrong memory regions when
-	  copying memory to/from the kernel (via copy_to_user() and
-	  copy_from_user() functions) by rejecting memory ranges that
-	  are larger than the specified heap object, span multiple
-	  separately allocated pages, are not on the process stack,
-	  or are part of the kernel text. This prevents entire classes
-	  of heap overflow exploits and similar kernel memory exposures.
-
 config FORTIFY_SOURCE
 	bool "Harden common str/mem functions against buffer overflows"
 	depends on ARCH_HAS_FORTIFY_SOURCE