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linux-next/mm/kasan/kasan.c
Mark Rutland e3ae116339 kasan: add functions to clear stack poison
Functions which the compiler has instrumented for ASAN place poison on
the stack shadow upon entry and remove this poison prior to returning.

In some cases (e.g. hotplug and idle), CPUs may exit the kernel a
number of levels deep in C code.  If there are any instrumented
functions on this critical path, these will leave portions of the idle
thread stack shadow poisoned.

If a CPU returns to the kernel via a different path (e.g. a cold
entry), then depending on stack frame layout subsequent calls to
instrumented functions may use regions of the stack with stale poison,
resulting in (spurious) KASAN splats to the console.

Contemporary GCCs always add stack shadow poisoning when ASAN is
enabled, even when asked to not instrument a function [1], so we can't
simply annotate functions on the critical path to avoid poisoning.

Instead, this series explicitly removes any stale poison before it can
be hit.  In the common hotplug case we clear the entire stack shadow in
common code, before a CPU is brought online.

On architectures which perform a cold return as part of cpu idle may
retain an architecture-specific amount of stack contents.  To retain the
poison for this retained context, the arch code must call the core KASAN
code, passing a "watermark" stack pointer value beyond which shadow will
be cleared.  Architectures which don't perform a cold return as part of
idle do not need any additional code.

This patch (of 3):

Functions which the compiler has instrumented for KASAN place poison on
the stack shadow upon entry and remove this poision prior to returning.

In some cases (e.g.  hotplug and idle), CPUs may exit the kernel a number
of levels deep in C code.  If there are any instrumented functions on this
critical path, these will leave portions of the stack shadow poisoned.

If a CPU returns to the kernel via a different path (e.g.  a cold entry),
then depending on stack frame layout subsequent calls to instrumented
functions may use regions of the stack with stale poison, resulting in
(spurious) KASAN splats to the console.

To avoid this, we must clear stale poison from the stack prior to
instrumented functions being called.  This patch adds functions to the
KASAN core for removing poison from (portions of) a task's stack.  These
will be used by subsequent patches to avoid problems with hotplug and
idle.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-09 15:43:42 -08:00

573 lines
13 KiB
C

/*
* This file contains shadow memory manipulation code.
*
* Copyright (c) 2014 Samsung Electronics Co., Ltd.
* Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
*
* Some code borrowed from https://github.com/xairy/kasan-prototype by
* Andrey Konovalov <adech.fo@gmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#define DISABLE_BRANCH_PROFILING
#include <linux/export.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kmemleak.h>
#include <linux/linkage.h>
#include <linux/memblock.h>
#include <linux/memory.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/stacktrace.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/vmalloc.h>
#include <linux/kasan.h>
#include "kasan.h"
#include "../slab.h"
/*
* Poisons the shadow memory for 'size' bytes starting from 'addr'.
* Memory addresses should be aligned to KASAN_SHADOW_SCALE_SIZE.
*/
static void kasan_poison_shadow(const void *address, size_t size, u8 value)
{
void *shadow_start, *shadow_end;
shadow_start = kasan_mem_to_shadow(address);
shadow_end = kasan_mem_to_shadow(address + size);
memset(shadow_start, value, shadow_end - shadow_start);
}
void kasan_unpoison_shadow(const void *address, size_t size)
{
kasan_poison_shadow(address, size, 0);
if (size & KASAN_SHADOW_MASK) {
u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
*shadow = size & KASAN_SHADOW_MASK;
}
}
static void __kasan_unpoison_stack(struct task_struct *task, void *sp)
{
void *base = task_stack_page(task);
size_t size = sp - base;
kasan_unpoison_shadow(base, size);
}
/* Unpoison the entire stack for a task. */
void kasan_unpoison_task_stack(struct task_struct *task)
{
__kasan_unpoison_stack(task, task_stack_page(task) + THREAD_SIZE);
}
/* Unpoison the stack for the current task beyond a watermark sp value. */
asmlinkage void kasan_unpoison_remaining_stack(void *sp)
{
__kasan_unpoison_stack(current, sp);
}
/*
* All functions below always inlined so compiler could
* perform better optimizations in each of __asan_loadX/__assn_storeX
* depending on memory access size X.
*/
static __always_inline bool memory_is_poisoned_1(unsigned long addr)
{
s8 shadow_value = *(s8 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(shadow_value)) {
s8 last_accessible_byte = addr & KASAN_SHADOW_MASK;
return unlikely(last_accessible_byte >= shadow_value);
}
return false;
}
static __always_inline bool memory_is_poisoned_2(unsigned long addr)
{
u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(*shadow_addr)) {
if (memory_is_poisoned_1(addr + 1))
return true;
/*
* If single shadow byte covers 2-byte access, we don't
* need to do anything more. Otherwise, test the first
* shadow byte.
*/
if (likely(((addr + 1) & KASAN_SHADOW_MASK) != 0))
return false;
return unlikely(*(u8 *)shadow_addr);
}
return false;
}
static __always_inline bool memory_is_poisoned_4(unsigned long addr)
{
u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(*shadow_addr)) {
if (memory_is_poisoned_1(addr + 3))
return true;
/*
* If single shadow byte covers 4-byte access, we don't
* need to do anything more. Otherwise, test the first
* shadow byte.
*/
if (likely(((addr + 3) & KASAN_SHADOW_MASK) >= 3))
return false;
return unlikely(*(u8 *)shadow_addr);
}
return false;
}
static __always_inline bool memory_is_poisoned_8(unsigned long addr)
{
u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(*shadow_addr)) {
if (memory_is_poisoned_1(addr + 7))
return true;
/*
* If single shadow byte covers 8-byte access, we don't
* need to do anything more. Otherwise, test the first
* shadow byte.
*/
if (likely(IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
return false;
return unlikely(*(u8 *)shadow_addr);
}
return false;
}
static __always_inline bool memory_is_poisoned_16(unsigned long addr)
{
u32 *shadow_addr = (u32 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(*shadow_addr)) {
u16 shadow_first_bytes = *(u16 *)shadow_addr;
if (unlikely(shadow_first_bytes))
return true;
/*
* If two shadow bytes covers 16-byte access, we don't
* need to do anything more. Otherwise, test the last
* shadow byte.
*/
if (likely(IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
return false;
return memory_is_poisoned_1(addr + 15);
}
return false;
}
static __always_inline unsigned long bytes_is_zero(const u8 *start,
size_t size)
{
while (size) {
if (unlikely(*start))
return (unsigned long)start;
start++;
size--;
}
return 0;
}
static __always_inline unsigned long memory_is_zero(const void *start,
const void *end)
{
unsigned int words;
unsigned long ret;
unsigned int prefix = (unsigned long)start % 8;
if (end - start <= 16)
return bytes_is_zero(start, end - start);
if (prefix) {
prefix = 8 - prefix;
ret = bytes_is_zero(start, prefix);
if (unlikely(ret))
return ret;
start += prefix;
}
words = (end - start) / 8;
while (words) {
if (unlikely(*(u64 *)start))
return bytes_is_zero(start, 8);
start += 8;
words--;
}
return bytes_is_zero(start, (end - start) % 8);
}
static __always_inline bool memory_is_poisoned_n(unsigned long addr,
size_t size)
{
unsigned long ret;
ret = memory_is_zero(kasan_mem_to_shadow((void *)addr),
kasan_mem_to_shadow((void *)addr + size - 1) + 1);
if (unlikely(ret)) {
unsigned long last_byte = addr + size - 1;
s8 *last_shadow = (s8 *)kasan_mem_to_shadow((void *)last_byte);
if (unlikely(ret != (unsigned long)last_shadow ||
((long)(last_byte & KASAN_SHADOW_MASK) >= *last_shadow)))
return true;
}
return false;
}
static __always_inline bool memory_is_poisoned(unsigned long addr, size_t size)
{
if (__builtin_constant_p(size)) {
switch (size) {
case 1:
return memory_is_poisoned_1(addr);
case 2:
return memory_is_poisoned_2(addr);
case 4:
return memory_is_poisoned_4(addr);
case 8:
return memory_is_poisoned_8(addr);
case 16:
return memory_is_poisoned_16(addr);
default:
BUILD_BUG();
}
}
return memory_is_poisoned_n(addr, size);
}
static __always_inline void check_memory_region(unsigned long addr,
size_t size, bool write)
{
if (unlikely(size == 0))
return;
if (unlikely((void *)addr <
kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
kasan_report(addr, size, write, _RET_IP_);
return;
}
if (likely(!memory_is_poisoned(addr, size)))
return;
kasan_report(addr, size, write, _RET_IP_);
}
void __asan_loadN(unsigned long addr, size_t size);
void __asan_storeN(unsigned long addr, size_t size);
#undef memset
void *memset(void *addr, int c, size_t len)
{
__asan_storeN((unsigned long)addr, len);
return __memset(addr, c, len);
}
#undef memmove
void *memmove(void *dest, const void *src, size_t len)
{
__asan_loadN((unsigned long)src, len);
__asan_storeN((unsigned long)dest, len);
return __memmove(dest, src, len);
}
#undef memcpy
void *memcpy(void *dest, const void *src, size_t len)
{
__asan_loadN((unsigned long)src, len);
__asan_storeN((unsigned long)dest, len);
return __memcpy(dest, src, len);
}
void kasan_alloc_pages(struct page *page, unsigned int order)
{
if (likely(!PageHighMem(page)))
kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
}
void kasan_free_pages(struct page *page, unsigned int order)
{
if (likely(!PageHighMem(page)))
kasan_poison_shadow(page_address(page),
PAGE_SIZE << order,
KASAN_FREE_PAGE);
}
void kasan_poison_slab(struct page *page)
{
kasan_poison_shadow(page_address(page),
PAGE_SIZE << compound_order(page),
KASAN_KMALLOC_REDZONE);
}
void kasan_unpoison_object_data(struct kmem_cache *cache, void *object)
{
kasan_unpoison_shadow(object, cache->object_size);
}
void kasan_poison_object_data(struct kmem_cache *cache, void *object)
{
kasan_poison_shadow(object,
round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE),
KASAN_KMALLOC_REDZONE);
}
void kasan_slab_alloc(struct kmem_cache *cache, void *object)
{
kasan_kmalloc(cache, object, cache->object_size);
}
void kasan_slab_free(struct kmem_cache *cache, void *object)
{
unsigned long size = cache->object_size;
unsigned long rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
/* RCU slabs could be legally used after free within the RCU period */
if (unlikely(cache->flags & SLAB_DESTROY_BY_RCU))
return;
kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
}
void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size)
{
unsigned long redzone_start;
unsigned long redzone_end;
if (unlikely(object == NULL))
return;
redzone_start = round_up((unsigned long)(object + size),
KASAN_SHADOW_SCALE_SIZE);
redzone_end = round_up((unsigned long)object + cache->object_size,
KASAN_SHADOW_SCALE_SIZE);
kasan_unpoison_shadow(object, size);
kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
KASAN_KMALLOC_REDZONE);
}
EXPORT_SYMBOL(kasan_kmalloc);
void kasan_kmalloc_large(const void *ptr, size_t size)
{
struct page *page;
unsigned long redzone_start;
unsigned long redzone_end;
if (unlikely(ptr == NULL))
return;
page = virt_to_page(ptr);
redzone_start = round_up((unsigned long)(ptr + size),
KASAN_SHADOW_SCALE_SIZE);
redzone_end = (unsigned long)ptr + (PAGE_SIZE << compound_order(page));
kasan_unpoison_shadow(ptr, size);
kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
KASAN_PAGE_REDZONE);
}
void kasan_krealloc(const void *object, size_t size)
{
struct page *page;
if (unlikely(object == ZERO_SIZE_PTR))
return;
page = virt_to_head_page(object);
if (unlikely(!PageSlab(page)))
kasan_kmalloc_large(object, size);
else
kasan_kmalloc(page->slab_cache, object, size);
}
void kasan_kfree(void *ptr)
{
struct page *page;
page = virt_to_head_page(ptr);
if (unlikely(!PageSlab(page)))
kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
KASAN_FREE_PAGE);
else
kasan_slab_free(page->slab_cache, ptr);
}
void kasan_kfree_large(const void *ptr)
{
struct page *page = virt_to_page(ptr);
kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
KASAN_FREE_PAGE);
}
int kasan_module_alloc(void *addr, size_t size)
{
void *ret;
size_t shadow_size;
unsigned long shadow_start;
shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
shadow_size = round_up(size >> KASAN_SHADOW_SCALE_SHIFT,
PAGE_SIZE);
if (WARN_ON(!PAGE_ALIGNED(shadow_start)))
return -EINVAL;
ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
shadow_start + shadow_size,
GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
__builtin_return_address(0));
if (ret) {
find_vm_area(addr)->flags |= VM_KASAN;
kmemleak_ignore(ret);
return 0;
}
return -ENOMEM;
}
void kasan_free_shadow(const struct vm_struct *vm)
{
if (vm->flags & VM_KASAN)
vfree(kasan_mem_to_shadow(vm->addr));
}
static void register_global(struct kasan_global *global)
{
size_t aligned_size = round_up(global->size, KASAN_SHADOW_SCALE_SIZE);
kasan_unpoison_shadow(global->beg, global->size);
kasan_poison_shadow(global->beg + aligned_size,
global->size_with_redzone - aligned_size,
KASAN_GLOBAL_REDZONE);
}
void __asan_register_globals(struct kasan_global *globals, size_t size)
{
int i;
for (i = 0; i < size; i++)
register_global(&globals[i]);
}
EXPORT_SYMBOL(__asan_register_globals);
void __asan_unregister_globals(struct kasan_global *globals, size_t size)
{
}
EXPORT_SYMBOL(__asan_unregister_globals);
#define DEFINE_ASAN_LOAD_STORE(size) \
void __asan_load##size(unsigned long addr) \
{ \
check_memory_region(addr, size, false); \
} \
EXPORT_SYMBOL(__asan_load##size); \
__alias(__asan_load##size) \
void __asan_load##size##_noabort(unsigned long); \
EXPORT_SYMBOL(__asan_load##size##_noabort); \
void __asan_store##size(unsigned long addr) \
{ \
check_memory_region(addr, size, true); \
} \
EXPORT_SYMBOL(__asan_store##size); \
__alias(__asan_store##size) \
void __asan_store##size##_noabort(unsigned long); \
EXPORT_SYMBOL(__asan_store##size##_noabort)
DEFINE_ASAN_LOAD_STORE(1);
DEFINE_ASAN_LOAD_STORE(2);
DEFINE_ASAN_LOAD_STORE(4);
DEFINE_ASAN_LOAD_STORE(8);
DEFINE_ASAN_LOAD_STORE(16);
void __asan_loadN(unsigned long addr, size_t size)
{
check_memory_region(addr, size, false);
}
EXPORT_SYMBOL(__asan_loadN);
__alias(__asan_loadN)
void __asan_loadN_noabort(unsigned long, size_t);
EXPORT_SYMBOL(__asan_loadN_noabort);
void __asan_storeN(unsigned long addr, size_t size)
{
check_memory_region(addr, size, true);
}
EXPORT_SYMBOL(__asan_storeN);
__alias(__asan_storeN)
void __asan_storeN_noabort(unsigned long, size_t);
EXPORT_SYMBOL(__asan_storeN_noabort);
/* to shut up compiler complaints */
void __asan_handle_no_return(void) {}
EXPORT_SYMBOL(__asan_handle_no_return);
#ifdef CONFIG_MEMORY_HOTPLUG
static int kasan_mem_notifier(struct notifier_block *nb,
unsigned long action, void *data)
{
return (action == MEM_GOING_ONLINE) ? NOTIFY_BAD : NOTIFY_OK;
}
static int __init kasan_memhotplug_init(void)
{
pr_err("WARNING: KASAN doesn't support memory hot-add\n");
pr_err("Memory hot-add will be disabled\n");
hotplug_memory_notifier(kasan_mem_notifier, 0);
return 0;
}
module_init(kasan_memhotplug_init);
#endif