[linux-block.git] / kernel / scs.c

// 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>
#include <asm/scs.h>

static struct kmem_cache *scs_cache;

static void *scs_alloc(int node)
{
	void *s;

	s = kmem_cache_alloc_node(scs_cache, GFP_SCS, node);
	if (s) {
		*__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);
	}

	return s;
}

static void scs_free(void *s)
{
	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);
}

static struct page *__scs_page(struct task_struct *tsk)
{
	return virt_to_page(task_scs(tsk));
}

static void scs_account(struct task_struct *tsk, int account)
{
	mod_zone_page_state(page_zone(__scs_page(tsk)), NR_KERNEL_SCS_KB,
		account * (SCS_SIZE / 1024));
}

int scs_prepare(struct task_struct *tsk, int node)
{
	void *s = scs_alloc(node);

	if (!s)
		return -ENOMEM;

	task_scs(tsk) = s;
	task_scs_offset(tsk) = 0;
	scs_account(tsk, 1);
	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++;
	}

	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(scs_corrupted(tsk), "corrupted shadow stack detected when freeing task\n");
	scs_check_usage(tsk);
	scs_account(tsk, -1);
	scs_free(s);
}
Commit	Line	Data
d08b9f0c ST	1	// SPDX-License-Identifier: GPL-2.0
	2	/*
	3	* Shadow Call Stack support.
	4	*
	5	* Copyright (C) 2019 Google LLC
	6	*/
	7
	8	#include <linux/kasan.h>
628d06a4	9	#include <linux/mm.h>
d08b9f0c ST	10	#include <linux/scs.h>
d08b9f0c ST	11	#include <linux/slab.h>
628d06a4	12	#include <linux/vmstat.h>
d08b9f0c ST	13	#include <asm/scs.h>
	14
	15	static struct kmem_cache *scs_cache;
	16
	17	static void *scs_alloc(int node)
	18	{
	19	void *s;
	20
	21	s = kmem_cache_alloc_node(scs_cache, GFP_SCS, node);
	22	if (s) {
	23	*__scs_magic(s) = SCS_END_MAGIC;
	24	/*
	25	* Poison the allocation to catch unintentional accesses to
	26	* the shadow stack when KASAN is enabled.
	27	*/
	28	kasan_poison_object_data(scs_cache, s);
	29	}
	30
	31	return s;
	32	}
	33
	34	static void scs_free(void *s)
	35	{
	36	kasan_unpoison_object_data(scs_cache, s);
	37	kmem_cache_free(scs_cache, s);
	38	}
	39
	40	void __init scs_init(void)
	41	{
	42	scs_cache = kmem_cache_create("scs_cache", SCS_SIZE, 0, 0, NULL);
	43	}
	44
628d06a4 ST	45	static struct page __scs_page(struct task_struct tsk)
	46	{
	47	return virt_to_page(task_scs(tsk));
	48	}
	49
	50	static void scs_account(struct task_struct *tsk, int account)
	51	{
	52	mod_zone_page_state(page_zone(__scs_page(tsk)), NR_KERNEL_SCS_KB,
	53	account * (SCS_SIZE / 1024));
	54	}
	55
d08b9f0c ST	56	int scs_prepare(struct task_struct *tsk, int node)
	57	{
	58	void *s = scs_alloc(node);
	59
	60	if (!s)
	61	return -ENOMEM;
	62
	63	task_scs(tsk) = s;
	64	task_scs_offset(tsk) = 0;
628d06a4	65	scs_account(tsk, 1);
d08b9f0c ST	66	return 0;
	67	}
	68
5bbaf9d1 ST	69	static void scs_check_usage(struct task_struct *tsk)
	70	{
	71	static unsigned long highest;
	72
	73	unsigned long *p, prev, curr = highest, used = 0;
	74
	75	if (!IS_ENABLED(CONFIG_DEBUG_STACK_USAGE))
	76	return;
	77
	78	for (p = task_scs(tsk); p < __scs_magic(tsk); ++p) {
	79	if (!READ_ONCE_NOCHECK(*p))
	80	break;
	81	used++;
	82	}
	83
	84	while (used > curr) {
	85	prev = cmpxchg_relaxed(&highest, curr, used);
	86
	87	if (prev == curr) {
	88	pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",
	89	tsk->comm, task_pid_nr(tsk), used);
	90	break;
	91	}
	92
	93	curr = prev;
	94	}
	95	}
	96
d08b9f0c ST	97	void scs_release(struct task_struct *tsk)
	98	{
	99	void *s = task_scs(tsk);
	100
	101	if (!s)
	102	return;
	103
	104	WARN(scs_corrupted(tsk), "corrupted shadow stack detected when freeing task\n");
5bbaf9d1	105	scs_check_usage(tsk);
628d06a4	106	scs_account(tsk, -1);
d08b9f0c ST	107	scs_free(s);
d08b9f0c ST	108	}