exec: Remove FOLL_FORCE for stack setup

It does not appear that FOLL_FORCE should be needed for setting up the
stack pages. They are allocated using the nascent brpm->vma, which was
newly created with VM_STACK_FLAGS, which an arch can override, but they
all appear to include VM_WRITE | VM_MAYWRITE. Remove FOLL_FORCE.

Cc: Eric Biederman <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lore.kernel.org/lkml/202211171439.CDE720EAD@keescook/
Signed-off-by: Kees Cook <[email protected]>

Author: kees

fs/exec.c

@@ -200,7 +200,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 {
 	struct page *page;
 	int ret;
-	unsigned int gup_flags = FOLL_FORCE;
+	unsigned int gup_flags = 0;
 
 #ifdef CONFIG_STACK_GROWSUP
 	if (write) {