execmem: don't remove ROX cache from the direct map

The memory allocated for the ROX cache was removed from the direct map to
reduce amount of direct map updates, however this cannot be tolerated by
/proc/kcore that accesses module memory using vread_iter() and the latter
does vmalloc_to_page() and copy_page_to_iter_nofault().

Instead of removing ROX cache memory from the direct map and mapping it as
ROX in vmalloc space, simply call set_memory_rox() that will take care of
proper permissions on both vmalloc and in the direct map.

Signed-off-by: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250126074733.1384926-5-rppt@kernel.org

mm/execmem.c

@@ -257,7 +257,6 @@ static void *__execmem_cache_alloc(struct execmem_range *range, size_t size)
 static int execmem_cache_populate(struct execmem_range *range, size_t size)
 {
 	unsigned long vm_flags = VM_ALLOW_HUGE_VMAP;
-	unsigned long start, end;
 	struct vm_struct *vm;
 	size_t alloc_size;
 	int err = -ENOMEM;
@@ -275,26 +274,18 @@ static int execmem_cache_populate(struct execmem_range *range, size_t size)
 	/* fill memory with instructions that will trap */
 	execmem_fill_trapping_insns(p, alloc_size, /* writable = */ true);
 
-	start = (unsigned long)p;
-	end = start + alloc_size;
-
-	vunmap_range(start, end);
-
-	err = execmem_set_direct_map_valid(vm, false);
-	if (err)
-		goto err_free_mem;
-
-	err = vmap_pages_range_noflush(start, end, range->pgprot, vm->pages,
-				       PMD_SHIFT);
+	err = set_memory_rox((unsigned long)p, vm->nr_pages);
 	if (err)
 		goto err_free_mem;
 
 	err = execmem_cache_add(p, alloc_size);
 	if (err)
-		goto err_free_mem;
+		goto err_reset_direct_map;
 
 	return 0;
 
+err_reset_direct_map:
+	execmem_set_direct_map_valid(vm, true);
 err_free_mem:
 	vfree(p);
 	return err;