155 lines
2.8 KiB
C
155 lines
2.8 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/cpuhotplug.h>
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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/vmalloc.h>
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#include <linux/vmstat.h>
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static void __scs_account(void *s, int account)
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{
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struct page *scs_page = vmalloc_to_page(s);
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mod_node_page_state(page_pgdat(scs_page), NR_KERNEL_SCS_KB,
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account * (SCS_SIZE / SZ_1K));
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}
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/* Matches NR_CACHED_STACKS for VMAP_STACK */
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#define NR_CACHED_SCS 2
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static DEFINE_PER_CPU(void *, scs_cache[NR_CACHED_SCS]);
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static void *__scs_alloc(int node)
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{
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int i;
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void *s;
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for (i = 0; i < NR_CACHED_SCS; i++) {
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s = this_cpu_xchg(scs_cache[i], NULL);
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if (s) {
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kasan_unpoison_vmalloc(s, SCS_SIZE);
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memset(s, 0, SCS_SIZE);
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return s;
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}
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}
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return __vmalloc_node_range(SCS_SIZE, 1, VMALLOC_START, VMALLOC_END,
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GFP_SCS, PAGE_KERNEL, 0, node,
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__builtin_return_address(0));
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}
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void *scs_alloc(int node)
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{
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void *s;
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s = __scs_alloc(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_vmalloc(s, SCS_SIZE);
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__scs_account(s, 1);
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return s;
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}
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void scs_free(void *s)
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{
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int i;
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__scs_account(s, -1);
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/*
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* We cannot sleep as this can be called in interrupt context,
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* so use this_cpu_cmpxchg to update the cache, and vfree_atomic
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* to free the stack.
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*/
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for (i = 0; i < NR_CACHED_SCS; i++)
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if (this_cpu_cmpxchg(scs_cache[i], 0, s) == NULL)
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return;
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kasan_unpoison_vmalloc(s, SCS_SIZE);
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vfree_atomic(s);
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}
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static int scs_cleanup(unsigned int cpu)
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{
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int i;
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void **cache = per_cpu_ptr(scs_cache, cpu);
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for (i = 0; i < NR_CACHED_SCS; i++) {
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vfree(cache[i]);
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cache[i] = NULL;
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}
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return 0;
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}
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void __init scs_init(void)
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{
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cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "scs:scs_cache", NULL,
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scs_cleanup);
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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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