// SPDX-License-Identifier: GPL-2.0/* * Shadow Call Stack support. * * Copyright (C) 2019 Google LLC */ #include <linux/kasan.h>#include <linux/mm.h>#include <linux/scs.h>#include <linux/slab.h>#include <linux/vmstat.h> static struct kmem_cache *scs_cache; static void __scs_account(void *s, int account){	struct page *scs_page = virt_to_page(s); 	mod_node_page_state(page_pgdat(scs_page), NR_KERNEL_SCS_KB,			    account * (SCS_SIZE / SZ_1K));} static void *scs_alloc(int node){	void *s = kmem_cache_alloc_node(scs_cache, GFP_SCS, node); 	if (!s)		return NULL; 	*__scs_magic(s) = SCS_END_MAGIC; 	/*	 * Poison the allocation to catch unintentional accesses to	 * the shadow stack when KASAN is enabled.	 */	kasan_poison_object_data(scs_cache, s);	__scs_account(s, 1);	return s;} static void scs_free(void *s){	__scs_account(s, -1);	kasan_unpoison_object_data(scs_cache, s);	kmem_cache_free(scs_cache, s);} void __init scs_init(void){	scs_cache = kmem_cache_create("scs_cache", SCS_SIZE, 0, 0, NULL);} int scs_prepare(struct task_struct *tsk, int node){	void *s = scs_alloc(node); 	if (!s)		return -ENOMEM; 	task_scs(tsk) = task_scs_sp(tsk) = s;	return 0;} static void scs_check_usage(struct task_struct *tsk){	static unsigned long highest; 	unsigned long *p, prev, curr = highest, used = 0; 	if (!IS_ENABLED(CONFIG_DEBUG_STACK_USAGE))		return; 	for (p = task_scs(tsk); p < __scs_magic(tsk); ++p) {		if (!READ_ONCE_NOCHECK(*p))			break;		used += sizeof(*p);	} 	while (used > curr) {		prev = cmpxchg_relaxed(&highest, curr, used); 		if (prev == curr) {			pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",				tsk->comm, task_pid_nr(tsk), used);			break;		} 		curr = prev;	}} void scs_release(struct task_struct *tsk){	void *s = task_scs(tsk); 	if (!s)		return; 	WARN(task_scs_end_corrupted(tsk),	     "corrupted shadow stack detected when freeing task\n");	scs_check_usage(tsk);	scs_free(s);}