fork: support VMAP_STACK with KASAN_VMALLOC

config VMAP_STACK

	default y

	bool "Use a virtually-mapped stack"

	depends on HAVE_ARCH_VMAP_STACK && !KASAN

	depends on HAVE_ARCH_VMAP_STACK

	depends on !KASAN || KASAN_VMALLOC

	---help---

	  Enable this if you want the use virtually-mapped kernel stacks

	  with guard pages.  This causes kernel stack overflows to be

	  caught immediately rather than causing difficult-to-diagnose

	  corruption.

	  This is presently incompatible with KASAN because KASAN expects

	  the stack to map directly to the KASAN shadow map using a formula

	  that is incorrect if the stack is in vmalloc space.

	  To use this with KASAN, the architecture must support backing

	  virtual mappings with real shadow memory, and KASAN_VMALLOC must

	  be enabled.

config ARCH_OPTIONAL_KERNEL_RWX

	def_bool n

#include <linux/livepatch.h>

#include <linux/thread_info.h>

#include <linux/stackleak.h>

#include <linux/kasan.h>

#include <asm/pgtable.h>

#include <asm/pgalloc.h>

		if (!s)

			continue;

		/* Clear the KASAN shadow of the stack. */

		kasan_unpoison_shadow(s->addr, THREAD_SIZE);

		/* Clear stale pointers from reused stack. */

		memset(s->addr, 0, THREAD_SIZE);