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![Andrey Konovalov](/assets/img/avatar_default.png)
HW_TAGS KASAN skips zeroing page_alloc allocations backing vmalloc
mappings via __GFP_SKIP_ZERO. Instead, these pages are zeroed via
kasan_unpoison_vmalloc() by passing the KASAN_VMALLOC_INIT flag.
The problem is that __kasan_unpoison_vmalloc() does not zero pages when
either kasan_vmalloc_enabled() or is_vmalloc_or_module_addr() fail.
Thus:
1. Change __vmalloc_node_range() to only set KASAN_VMALLOC_INIT when
__GFP_SKIP_ZERO is set.
2. Change __kasan_unpoison_vmalloc() to always zero pages when the
KASAN_VMALLOC_INIT flag is set.
3. Add WARN_ON() asserts to check that KASAN_VMALLOC_INIT cannot be set
in other early return paths of __kasan_unpoison_vmalloc().
Also clean up the comment in __kasan_unpoison_vmalloc.
Link: https://lkml.kernel.org/r/4bc503537efdc539ffc3f461c1b70162eea31cf6.1654798516.git.andreyknvl@google.com
Fixes: 23689e91fb
("kasan, vmalloc: add vmalloc tagging for HW_TAGS")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
373 lines
9.1 KiB
C
373 lines
9.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* This file contains core hardware tag-based KASAN code.
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*
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* Copyright (c) 2020 Google, Inc.
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* Author: Andrey Konovalov <andreyknvl@google.com>
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*/
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#define pr_fmt(fmt) "kasan: " fmt
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#include <linux/init.h>
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#include <linux/kasan.h>
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#include <linux/kernel.h>
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#include <linux/memory.h>
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#include <linux/mm.h>
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#include <linux/static_key.h>
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#include <linux/string.h>
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#include <linux/types.h>
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#include "kasan.h"
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enum kasan_arg {
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KASAN_ARG_DEFAULT,
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KASAN_ARG_OFF,
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KASAN_ARG_ON,
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};
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enum kasan_arg_mode {
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KASAN_ARG_MODE_DEFAULT,
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KASAN_ARG_MODE_SYNC,
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KASAN_ARG_MODE_ASYNC,
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KASAN_ARG_MODE_ASYMM,
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};
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enum kasan_arg_vmalloc {
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KASAN_ARG_VMALLOC_DEFAULT,
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KASAN_ARG_VMALLOC_OFF,
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KASAN_ARG_VMALLOC_ON,
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};
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enum kasan_arg_stacktrace {
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KASAN_ARG_STACKTRACE_DEFAULT,
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KASAN_ARG_STACKTRACE_OFF,
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KASAN_ARG_STACKTRACE_ON,
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};
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static enum kasan_arg kasan_arg __ro_after_init;
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static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
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static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
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static enum kasan_arg_stacktrace kasan_arg_stacktrace __initdata;
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/*
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* Whether KASAN is enabled at all.
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* The value remains false until KASAN is initialized by kasan_init_hw_tags().
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*/
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DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
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EXPORT_SYMBOL(kasan_flag_enabled);
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/*
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* Whether the selected mode is synchronous, asynchronous, or asymmetric.
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* Defaults to KASAN_MODE_SYNC.
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*/
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enum kasan_mode kasan_mode __ro_after_init;
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EXPORT_SYMBOL_GPL(kasan_mode);
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/* Whether to enable vmalloc tagging. */
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DEFINE_STATIC_KEY_TRUE(kasan_flag_vmalloc);
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/* Whether to collect alloc/free stack traces. */
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DEFINE_STATIC_KEY_TRUE(kasan_flag_stacktrace);
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/* kasan=off/on */
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static int __init early_kasan_flag(char *arg)
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{
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if (!arg)
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return -EINVAL;
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if (!strcmp(arg, "off"))
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kasan_arg = KASAN_ARG_OFF;
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else if (!strcmp(arg, "on"))
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kasan_arg = KASAN_ARG_ON;
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else
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return -EINVAL;
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return 0;
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}
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early_param("kasan", early_kasan_flag);
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/* kasan.mode=sync/async/asymm */
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static int __init early_kasan_mode(char *arg)
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{
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if (!arg)
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return -EINVAL;
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if (!strcmp(arg, "sync"))
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kasan_arg_mode = KASAN_ARG_MODE_SYNC;
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else if (!strcmp(arg, "async"))
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kasan_arg_mode = KASAN_ARG_MODE_ASYNC;
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else if (!strcmp(arg, "asymm"))
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kasan_arg_mode = KASAN_ARG_MODE_ASYMM;
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else
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return -EINVAL;
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return 0;
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}
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early_param("kasan.mode", early_kasan_mode);
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/* kasan.vmalloc=off/on */
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static int __init early_kasan_flag_vmalloc(char *arg)
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{
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if (!arg)
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return -EINVAL;
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if (!strcmp(arg, "off"))
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kasan_arg_vmalloc = KASAN_ARG_VMALLOC_OFF;
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else if (!strcmp(arg, "on"))
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kasan_arg_vmalloc = KASAN_ARG_VMALLOC_ON;
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else
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return -EINVAL;
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return 0;
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}
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early_param("kasan.vmalloc", early_kasan_flag_vmalloc);
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/* kasan.stacktrace=off/on */
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static int __init early_kasan_flag_stacktrace(char *arg)
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{
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if (!arg)
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return -EINVAL;
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if (!strcmp(arg, "off"))
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kasan_arg_stacktrace = KASAN_ARG_STACKTRACE_OFF;
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else if (!strcmp(arg, "on"))
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kasan_arg_stacktrace = KASAN_ARG_STACKTRACE_ON;
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else
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return -EINVAL;
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return 0;
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}
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early_param("kasan.stacktrace", early_kasan_flag_stacktrace);
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static inline const char *kasan_mode_info(void)
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{
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if (kasan_mode == KASAN_MODE_ASYNC)
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return "async";
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else if (kasan_mode == KASAN_MODE_ASYMM)
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return "asymm";
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else
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return "sync";
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}
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/*
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* kasan_init_hw_tags_cpu() is called for each CPU.
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* Not marked as __init as a CPU can be hot-plugged after boot.
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*/
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void kasan_init_hw_tags_cpu(void)
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{
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/*
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* There's no need to check that the hardware is MTE-capable here,
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* as this function is only called for MTE-capable hardware.
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*/
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/*
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* If KASAN is disabled via command line, don't initialize it.
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* When this function is called, kasan_flag_enabled is not yet
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* set by kasan_init_hw_tags(). Thus, check kasan_arg instead.
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*/
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if (kasan_arg == KASAN_ARG_OFF)
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return;
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/*
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* Enable async or asymm modes only when explicitly requested
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* through the command line.
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*/
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kasan_enable_tagging();
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}
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/* kasan_init_hw_tags() is called once on boot CPU. */
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void __init kasan_init_hw_tags(void)
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{
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/* If hardware doesn't support MTE, don't initialize KASAN. */
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if (!system_supports_mte())
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return;
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/* If KASAN is disabled via command line, don't initialize it. */
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if (kasan_arg == KASAN_ARG_OFF)
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return;
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switch (kasan_arg_mode) {
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case KASAN_ARG_MODE_DEFAULT:
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/* Default is specified by kasan_mode definition. */
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break;
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case KASAN_ARG_MODE_SYNC:
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kasan_mode = KASAN_MODE_SYNC;
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break;
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case KASAN_ARG_MODE_ASYNC:
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kasan_mode = KASAN_MODE_ASYNC;
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break;
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case KASAN_ARG_MODE_ASYMM:
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kasan_mode = KASAN_MODE_ASYMM;
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break;
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}
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switch (kasan_arg_vmalloc) {
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case KASAN_ARG_VMALLOC_DEFAULT:
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/* Default is specified by kasan_flag_vmalloc definition. */
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break;
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case KASAN_ARG_VMALLOC_OFF:
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static_branch_disable(&kasan_flag_vmalloc);
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break;
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case KASAN_ARG_VMALLOC_ON:
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static_branch_enable(&kasan_flag_vmalloc);
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break;
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}
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switch (kasan_arg_stacktrace) {
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case KASAN_ARG_STACKTRACE_DEFAULT:
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/* Default is specified by kasan_flag_stacktrace definition. */
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break;
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case KASAN_ARG_STACKTRACE_OFF:
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static_branch_disable(&kasan_flag_stacktrace);
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break;
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case KASAN_ARG_STACKTRACE_ON:
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static_branch_enable(&kasan_flag_stacktrace);
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break;
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}
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/* KASAN is now initialized, enable it. */
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static_branch_enable(&kasan_flag_enabled);
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pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, vmalloc=%s, stacktrace=%s)\n",
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kasan_mode_info(),
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kasan_vmalloc_enabled() ? "on" : "off",
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kasan_stack_collection_enabled() ? "on" : "off");
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}
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#ifdef CONFIG_KASAN_VMALLOC
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static void unpoison_vmalloc_pages(const void *addr, u8 tag)
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{
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struct vm_struct *area;
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int i;
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/*
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* As hardware tag-based KASAN only tags VM_ALLOC vmalloc allocations
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* (see the comment in __kasan_unpoison_vmalloc), all of the pages
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* should belong to a single area.
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*/
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area = find_vm_area((void *)addr);
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if (WARN_ON(!area))
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return;
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for (i = 0; i < area->nr_pages; i++) {
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struct page *page = area->pages[i];
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page_kasan_tag_set(page, tag);
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}
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}
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static void init_vmalloc_pages(const void *start, unsigned long size)
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{
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const void *addr;
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for (addr = start; addr < start + size; addr += PAGE_SIZE) {
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struct page *page = virt_to_page(addr);
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clear_highpage_kasan_tagged(page);
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}
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}
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void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
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kasan_vmalloc_flags_t flags)
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{
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u8 tag;
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unsigned long redzone_start, redzone_size;
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if (!kasan_vmalloc_enabled() || !is_vmalloc_or_module_addr(start)) {
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if (flags & KASAN_VMALLOC_INIT)
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init_vmalloc_pages(start, size);
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return (void *)start;
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}
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/*
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* Don't tag non-VM_ALLOC mappings, as:
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*
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* 1. Unlike the software KASAN modes, hardware tag-based KASAN only
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* supports tagging physical memory. Therefore, it can only tag a
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* single mapping of normal physical pages.
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* 2. Hardware tag-based KASAN can only tag memory mapped with special
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* mapping protection bits, see arch_vmap_pgprot_tagged().
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* As non-VM_ALLOC mappings can be mapped outside of vmalloc code,
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* providing these bits would require tracking all non-VM_ALLOC
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* mappers.
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*
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* Thus, for VM_ALLOC mappings, hardware tag-based KASAN only tags
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* the first virtual mapping, which is created by vmalloc().
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* Tagging the page_alloc memory backing that vmalloc() allocation is
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* skipped, see ___GFP_SKIP_KASAN_UNPOISON.
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*
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* For non-VM_ALLOC allocations, page_alloc memory is tagged as usual.
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*/
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if (!(flags & KASAN_VMALLOC_VM_ALLOC)) {
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WARN_ON(flags & KASAN_VMALLOC_INIT);
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return (void *)start;
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}
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/*
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* Don't tag executable memory.
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* The kernel doesn't tolerate having the PC register tagged.
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*/
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if (!(flags & KASAN_VMALLOC_PROT_NORMAL)) {
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WARN_ON(flags & KASAN_VMALLOC_INIT);
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return (void *)start;
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}
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tag = kasan_random_tag();
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start = set_tag(start, tag);
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/* Unpoison and initialize memory up to size. */
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kasan_unpoison(start, size, flags & KASAN_VMALLOC_INIT);
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/*
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* Explicitly poison and initialize the in-page vmalloc() redzone.
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* Unlike software KASAN modes, hardware tag-based KASAN doesn't
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* unpoison memory when populating shadow for vmalloc() space.
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*/
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redzone_start = round_up((unsigned long)start + size,
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KASAN_GRANULE_SIZE);
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redzone_size = round_up(redzone_start, PAGE_SIZE) - redzone_start;
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kasan_poison((void *)redzone_start, redzone_size, KASAN_TAG_INVALID,
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flags & KASAN_VMALLOC_INIT);
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/*
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* Set per-page tag flags to allow accessing physical memory for the
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* vmalloc() mapping through page_address(vmalloc_to_page()).
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*/
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unpoison_vmalloc_pages(start, tag);
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return (void *)start;
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}
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void __kasan_poison_vmalloc(const void *start, unsigned long size)
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{
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/*
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* No tagging here.
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* The physical pages backing the vmalloc() allocation are poisoned
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* through the usual page_alloc paths.
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*/
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}
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#endif
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void kasan_enable_tagging(void)
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{
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if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
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hw_enable_tagging_async();
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else if (kasan_arg_mode == KASAN_ARG_MODE_ASYMM)
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hw_enable_tagging_asymm();
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else
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hw_enable_tagging_sync();
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}
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#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
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EXPORT_SYMBOL_GPL(kasan_enable_tagging);
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void kasan_force_async_fault(void)
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{
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hw_force_async_tag_fault();
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}
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EXPORT_SYMBOL_GPL(kasan_force_async_fault);
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#endif
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