linux/kernel/scs.c
Will Deacon 333ed74689 scs: Report SCS usage in bytes rather than number of entries
Fix the SCS debug usage check so that we report the number of bytes
used, rather than the number of entries.

Fixes: 5bbaf9d1fc ("scs: Add support for stack usage debugging")
Reported-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Will Deacon <will@kernel.org>
2020-06-04 16:14:56 +01:00

105 lines
1.9 KiB
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>
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 += 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);
}