Revert "mm: add arch hook to validate mmap() prot flags"

This reverts commit cb1a393.

Since the arm64 WXN patch has been reverted, remove this hook as it
would not have any users.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/ZfGESD3a91lxH367@arm.com

Author: ctmarinas

include/linux/mman.h

@@ -124,21 +124,6 @@ static inline bool arch_validate_flags(unsigned long flags)
 #define arch_validate_flags arch_validate_flags
 #endif
 
-#ifndef arch_validate_mmap_prot
-/*
- * This is called from mmap(), which ignores unknown prot bits so the default
- * is to accept anything.
- *
- * Returns true if the prot flags are valid
- */
-static inline bool arch_validate_mmap_prot(unsigned long prot,
-					   unsigned long addr)
-{
-	return true;
-}
-#define arch_validate_mmap_prot arch_validate_mmap_prot
-#endif
-
 /*
  * Optimisation macro.  It is equivalent to:
  *      (x & bit1) ? bit2 : 0

mm/mmap.c

@@ -1229,9 +1229,6 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 		if (!(file && path_noexec(&file->f_path)))
 			prot |= PROT_EXEC;
 
-	if (!arch_validate_mmap_prot(prot, addr))
-		return -EACCES;
-
 	/* force arch specific MAP_FIXED handling in get_unmapped_area */
 	if (flags & MAP_FIXED_NOREPLACE)
 		flags |= MAP_FIXED;