5bbaf9d1fc
Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. When enabled, also prints out the highest shadow stack usage per process. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Acked-by: Will Deacon <will@kernel.org> [will: rewrote most of scs_check_usage()] Signed-off-by: Will Deacon <will@kernel.org>
109 lines
2.0 KiB
C
109 lines
2.0 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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#include <asm/scs.h>
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static struct kmem_cache *scs_cache;
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static void *scs_alloc(int node)
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{
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void *s;
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s = kmem_cache_alloc_node(scs_cache, GFP_SCS, node);
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if (s) {
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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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}
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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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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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static struct page *__scs_page(struct task_struct *tsk)
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{
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return virt_to_page(task_scs(tsk));
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}
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static void scs_account(struct task_struct *tsk, int account)
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{
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mod_zone_page_state(page_zone(__scs_page(tsk)), NR_KERNEL_SCS_KB,
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account * (SCS_SIZE / 1024));
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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) = s;
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task_scs_offset(tsk) = 0;
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scs_account(tsk, 1);
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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++;
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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(scs_corrupted(tsk), "corrupted shadow stack detected when freeing task\n");
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scs_check_usage(tsk);
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scs_account(tsk, -1);
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scs_free(s);
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}
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