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// 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_zone_page_state(page_zone(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++;
}
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);
}
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