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333ed74689
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>
105 lines
1.9 KiB
C
105 lines
1.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Shadow Call Stack support.
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*
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* Copyright (C) 2019 Google LLC
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*/
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#include <linux/kasan.h>
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#include <linux/mm.h>
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#include <linux/scs.h>
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#include <linux/slab.h>
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#include <linux/vmstat.h>
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static struct kmem_cache *scs_cache;
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static void __scs_account(void *s, int account)
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{
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struct page *scs_page = virt_to_page(s);
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mod_zone_page_state(page_zone(scs_page), NR_KERNEL_SCS_KB,
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account * (SCS_SIZE / SZ_1K));
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}
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static void *scs_alloc(int node)
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{
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void *s = kmem_cache_alloc_node(scs_cache, GFP_SCS, node);
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if (!s)
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return NULL;
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*__scs_magic(s) = SCS_END_MAGIC;
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/*
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* Poison the allocation to catch unintentional accesses to
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* the shadow stack when KASAN is enabled.
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*/
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kasan_poison_object_data(scs_cache, s);
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__scs_account(s, 1);
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return s;
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}
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static void scs_free(void *s)
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{
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__scs_account(s, -1);
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kasan_unpoison_object_data(scs_cache, s);
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kmem_cache_free(scs_cache, s);
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}
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void __init scs_init(void)
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{
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scs_cache = kmem_cache_create("scs_cache", SCS_SIZE, 0, 0, NULL);
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}
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int scs_prepare(struct task_struct *tsk, int node)
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{
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void *s = scs_alloc(node);
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if (!s)
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return -ENOMEM;
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task_scs(tsk) = task_scs_sp(tsk) = s;
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return 0;
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}
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static void scs_check_usage(struct task_struct *tsk)
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{
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static unsigned long highest;
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unsigned long *p, prev, curr = highest, used = 0;
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if (!IS_ENABLED(CONFIG_DEBUG_STACK_USAGE))
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return;
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for (p = task_scs(tsk); p < __scs_magic(tsk); ++p) {
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if (!READ_ONCE_NOCHECK(*p))
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break;
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used += sizeof(*p);
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}
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while (used > curr) {
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prev = cmpxchg_relaxed(&highest, curr, used);
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if (prev == curr) {
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pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",
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tsk->comm, task_pid_nr(tsk), used);
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break;
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}
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curr = prev;
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}
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}
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void scs_release(struct task_struct *tsk)
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{
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void *s = task_scs(tsk);
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if (!s)
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return;
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WARN(task_scs_end_corrupted(tsk),
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"corrupted shadow stack detected when freeing task\n");
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scs_check_usage(tsk);
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scs_free(s);
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}
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