[linux-2.6-microblaze.git] / mm / kasan / common.c

// SPDX-License-Identifier: GPL-2.0
/*
 * This file contains common generic and tag-based KASAN 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 <andreyknvl@gmail.com>
 */

#include <linux/export.h>
#include <linux/init.h>
#include <linux/kasan.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/sched/task_stack.h>
#include <linux/slab.h>
#include <linux/stacktrace.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/vmalloc.h>
#include <linux/bug.h>

#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

#include "kasan.h"
#include "../slab.h"

depot_stack_handle_t kasan_save_stack(gfp_t flags)
{
        unsigned long entries[KASAN_STACK_DEPTH];
        unsigned int nr_entries;

        nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
        nr_entries = filter_irq_stacks(entries, nr_entries);
        return stack_depot_save(entries, nr_entries, flags);
}

void kasan_set_track(struct kasan_track *track, gfp_t flags)
{
        track->pid = current->pid;
        track->stack = kasan_save_stack(flags);
}

void kasan_enable_current(void)
{
        current->kasan_depth++;
}

void kasan_disable_current(void)
{
        current->kasan_depth--;
}

bool __kasan_check_read(const volatile void *p, unsigned int size)
{
        return check_memory_region((unsigned long)p, size, false, _RET_IP_);
}
EXPORT_SYMBOL(__kasan_check_read);

bool __kasan_check_write(const volatile void *p, unsigned int size)
{
        return check_memory_region((unsigned long)p, size, true, _RET_IP_);
}
EXPORT_SYMBOL(__kasan_check_write);

#undef memset
void *memset(void *addr, int c, size_t len)
{
        if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_))
                return NULL;

        return __memset(addr, c, len);
}

#ifdef __HAVE_ARCH_MEMMOVE
#undef memmove
void *memmove(void *dest, const void *src, size_t len)
{
        if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
            !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
                return NULL;

        return __memmove(dest, src, len);
}
#endif

#undef memcpy
void *memcpy(void *dest, const void *src, size_t len)
{
        if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
            !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
                return NULL;

        return __memcpy(dest, src, len);
}

/*
 * Poisons the shadow memory for 'size' bytes starting from 'addr'.
 * Memory addresses should be aligned to KASAN_SHADOW_SCALE_SIZE.
 */
void kasan_poison_shadow(const void *address, size_t size, u8 value)
{
        void *shadow_start, *shadow_end;

        /*
         * Perform shadow offset calculation based on untagged address, as
         * some of the callers (e.g. kasan_poison_object_data) pass tagged
         * addresses to this function.
         */
        address = reset_tag(address);

        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)
{
        u8 tag = get_tag(address);

        /*
         * Perform shadow offset calculation based on untagged address, as
         * some of the callers (e.g. kasan_unpoison_object_data) pass tagged
         * addresses to this function.
         */
        address = reset_tag(address);

        kasan_poison_shadow(address, size, tag);

        if (size & KASAN_SHADOW_MASK) {
                u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);

                if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
                        *shadow = tag;
                else
                        *shadow = size & KASAN_SHADOW_MASK;
        }
}

static void __kasan_unpoison_stack(struct task_struct *task, const 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_task_stack_below(const void *watermark)
{
        /*
         * Calculate the task stack base address.  Avoid using 'current'
         * because this function is called by early resume code which hasn't
         * yet set up the percpu register (%gs).
         */
        void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));

        kasan_unpoison_shadow(base, watermark - base);
}

void kasan_alloc_pages(struct page *page, unsigned int order)
{
        u8 tag;
        unsigned long i;

        if (unlikely(PageHighMem(page)))
                return;

        tag = random_tag();
        for (i = 0; i < (1 << order); i++)
                page_kasan_tag_set(page + i, tag);
        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);
}

/*
 * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
 * For larger allocations larger redzones are used.
 */
static inline unsigned int optimal_redzone(unsigned int object_size)
{
        if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
                return 0;

        return
                object_size <= 64        - 16   ? 16 :
                object_size <= 128       - 32   ? 32 :
                object_size <= 512       - 64   ? 64 :
                object_size <= 4096      - 128  ? 128 :
                object_size <= (1 << 14) - 256  ? 256 :
                object_size <= (1 << 15) - 512  ? 512 :
                object_size <= (1 << 16) - 1024 ? 1024 : 2048;
}

void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
                        slab_flags_t *flags)
{
        unsigned int orig_size = *size;
        unsigned int redzone_size;
        int redzone_adjust;

        /* Add alloc meta. */
        cache->kasan_info.alloc_meta_offset = *size;
        *size += sizeof(struct kasan_alloc_meta);

        /* Add free meta. */
        if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
            (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
             cache->object_size < sizeof(struct kasan_free_meta))) {
                cache->kasan_info.free_meta_offset = *size;
                *size += sizeof(struct kasan_free_meta);
        }

        redzone_size = optimal_redzone(cache->object_size);
        redzone_adjust = redzone_size - (*size - cache->object_size);
        if (redzone_adjust > 0)
                *size += redzone_adjust;

        *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
                        max(*size, cache->object_size + redzone_size));

        /*
         * If the metadata doesn't fit, don't enable KASAN at all.
         */
        if (*size <= cache->kasan_info.alloc_meta_offset ||
                        *size <= cache->kasan_info.free_meta_offset) {
                cache->kasan_info.alloc_meta_offset = 0;
                cache->kasan_info.free_meta_offset = 0;
                *size = orig_size;
                return;
        }

        *flags |= SLAB_KASAN;
}

size_t kasan_metadata_size(struct kmem_cache *cache)
{
        return (cache->kasan_info.alloc_meta_offset ?
                sizeof(struct kasan_alloc_meta) : 0) +
                (cache->kasan_info.free_meta_offset ?
                sizeof(struct kasan_free_meta) : 0);
}

struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
                                        const void *object)
{
        return (void *)object + cache->kasan_info.alloc_meta_offset;
}

struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
                                      const void *object)
{
        BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
        return (void *)object + cache->kasan_info.free_meta_offset;
}

void kasan_poison_slab(struct page *page)
{
        unsigned long i;

        for (i = 0; i < compound_nr(page); i++)
                page_kasan_tag_reset(page + i);
        kasan_poison_shadow(page_address(page), page_size(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);
}

/*
 * This function assigns a tag to an object considering the following:
 * 1. A cache might have a constructor, which might save a pointer to a slab
 *    object somewhere (e.g. in the object itself). We preassign a tag for
 *    each object in caches with constructors during slab creation and reuse
 *    the same tag each time a particular object is allocated.
 * 2. A cache might be SLAB_TYPESAFE_BY_RCU, which means objects can be
 *    accessed after being freed. We preassign tags for objects in these
 *    caches as well.
 * 3. For SLAB allocator we can't preassign tags randomly since the freelist
 *    is stored as an array of indexes instead of a linked list. Assign tags
 *    based on objects indexes, so that objects that are next to each other
 *    get different tags.
 */
static u8 assign_tag(struct kmem_cache *cache, const void *object,
                        bool init, bool keep_tag)
{
        /*
         * 1. When an object is kmalloc()'ed, two hooks are called:
         *    kasan_slab_alloc() and kasan_kmalloc(). We assign the
         *    tag only in the first one.
         * 2. We reuse the same tag for krealloc'ed objects.
         */
        if (keep_tag)
                return get_tag(object);

        /*
         * If the cache neither has a constructor nor has SLAB_TYPESAFE_BY_RCU
         * set, assign a tag when the object is being allocated (init == false).
         */
        if (!cache->ctor && !(cache->flags & SLAB_TYPESAFE_BY_RCU))
                return init ? KASAN_TAG_KERNEL : random_tag();

        /* For caches that either have a constructor or SLAB_TYPESAFE_BY_RCU: */
#ifdef CONFIG_SLAB
        /* For SLAB assign tags based on the object index in the freelist. */
        return (u8)obj_to_index(cache, virt_to_page(object), (void *)object);
#else
        /*
         * For SLUB assign a random tag during slab creation, otherwise reuse
         * the already assigned tag.
         */
        return init ? random_tag() : get_tag(object);
#endif
}

void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
                                                const void *object)
{
        struct kasan_alloc_meta *alloc_info;

        if (!(cache->flags & SLAB_KASAN))
                return (void *)object;

        alloc_info = get_alloc_info(cache, object);
        __memset(alloc_info, 0, sizeof(*alloc_info));

        if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
                object = set_tag(object,
                                assign_tag(cache, object, true, false));

        return (void *)object;
}

static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
{
        if (IS_ENABLED(CONFIG_KASAN_GENERIC))
                return shadow_byte < 0 ||
                        shadow_byte >= KASAN_SHADOW_SCALE_SIZE;

        /* else CONFIG_KASAN_SW_TAGS: */
        if ((u8)shadow_byte == KASAN_TAG_INVALID)
                return true;
        if ((tag != KASAN_TAG_KERNEL) && (tag != (u8)shadow_byte))
                return true;

        return false;
}

static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
                              unsigned long ip, bool quarantine)
{
        s8 shadow_byte;
        u8 tag;
        void *tagged_object;
        unsigned long rounded_up_size;

        tag = get_tag(object);
        tagged_object = object;
        object = reset_tag(object);

        if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
            object)) {
                kasan_report_invalid_free(tagged_object, ip);
                return true;
        }

        /* RCU slabs could be legally used after free within the RCU period */
        if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
                return false;

        shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
        if (shadow_invalid(tag, shadow_byte)) {
                kasan_report_invalid_free(tagged_object, ip);
                return true;
        }

        rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
        kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);

        if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
                        unlikely(!(cache->flags & SLAB_KASAN)))
                return false;

        kasan_set_free_info(cache, object, tag);

        quarantine_put(get_free_info(cache, object), cache);

        return IS_ENABLED(CONFIG_KASAN_GENERIC);
}

bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
{
        return __kasan_slab_free(cache, object, ip, true);
}

static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
                                size_t size, gfp_t flags, bool keep_tag)
{
        unsigned long redzone_start;
        unsigned long redzone_end;
        u8 tag = 0xff;

        if (gfpflags_allow_blocking(flags))
                quarantine_reduce();

        if (unlikely(object == NULL))
                return NULL;

        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);

        if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
                tag = assign_tag(cache, object, false, keep_tag);

        /* Tag is ignored in set_tag without CONFIG_KASAN_SW_TAGS */
        kasan_unpoison_shadow(set_tag(object, tag), size);
        kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
                KASAN_KMALLOC_REDZONE);

        if (cache->flags & SLAB_KASAN)
                kasan_set_track(&get_alloc_info(cache, object)->alloc_track, flags);

        return set_tag(object, tag);
}

void * __must_check kasan_slab_alloc(struct kmem_cache *cache, void *object,
                                        gfp_t flags)
{
        return __kasan_kmalloc(cache, object, cache->object_size, flags, false);
}

void * __must_check kasan_kmalloc(struct kmem_cache *cache, const void *object,
                                size_t size, gfp_t flags)
{
        return __kasan_kmalloc(cache, object, size, flags, true);
}
EXPORT_SYMBOL(kasan_kmalloc);

void * __must_check kasan_kmalloc_large(const void *ptr, size_t size,
                                                gfp_t flags)
{
        struct page *page;
        unsigned long redzone_start;
        unsigned long redzone_end;

        if (gfpflags_allow_blocking(flags))
                quarantine_reduce();

        if (unlikely(ptr == NULL))
                return NULL;

        page = virt_to_page(ptr);
        redzone_start = round_up((unsigned long)(ptr + size),
                                KASAN_SHADOW_SCALE_SIZE);
        redzone_end = (unsigned long)ptr + page_size(page);

        kasan_unpoison_shadow(ptr, size);
        kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
                KASAN_PAGE_REDZONE);

        return (void *)ptr;
}

void * __must_check kasan_krealloc(const void *object, size_t size, gfp_t flags)
{
        struct page *page;

        if (unlikely(object == ZERO_SIZE_PTR))
                return (void *)object;

        page = virt_to_head_page(object);

        if (unlikely(!PageSlab(page)))
                return kasan_kmalloc_large(object, size, flags);
        else
                return __kasan_kmalloc(page->slab_cache, object, size,
                                                flags, true);
}

void kasan_poison_kfree(void *ptr, unsigned long ip)
{
        struct page *page;

        page = virt_to_head_page(ptr);

        if (unlikely(!PageSlab(page))) {
                if (ptr != page_address(page)) {
                        kasan_report_invalid_free(ptr, ip);
                        return;
                }
                kasan_poison_shadow(ptr, page_size(page), KASAN_FREE_PAGE);
        } else {
                __kasan_slab_free(page->slab_cache, ptr, ip, false);
        }
}

void kasan_kfree_large(void *ptr, unsigned long ip)
{
        if (ptr != page_address(virt_to_head_page(ptr)))
                kasan_report_invalid_free(ptr, ip);
        /* The object will be poisoned by page_alloc. */
}

#ifndef CONFIG_KASAN_VMALLOC
int kasan_module_alloc(void *addr, size_t size)
{
        void *ret;
        size_t scaled_size;
        size_t shadow_size;
        unsigned long shadow_start;

        shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
        scaled_size = (size + KASAN_SHADOW_MASK) >> KASAN_SHADOW_SCALE_SHIFT;
        shadow_size = round_up(scaled_size, 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,
                        PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
                        __builtin_return_address(0));

        if (ret) {
                __memset(ret, KASAN_SHADOW_INIT, shadow_size);
                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));
}
#endif

#ifdef CONFIG_MEMORY_HOTPLUG
static bool shadow_mapped(unsigned long addr)
{
        pgd_t *pgd = pgd_offset_k(addr);
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

        if (pgd_none(*pgd))
                return false;
        p4d = p4d_offset(pgd, addr);
        if (p4d_none(*p4d))
                return false;
        pud = pud_offset(p4d, addr);
        if (pud_none(*pud))
                return false;

        /*
         * We can't use pud_large() or pud_huge(), the first one is
         * arch-specific, the last one depends on HUGETLB_PAGE.  So let's abuse
         * pud_bad(), if pud is bad then it's bad because it's huge.
         */
        if (pud_bad(*pud))
                return true;
        pmd = pmd_offset(pud, addr);
        if (pmd_none(*pmd))
                return false;

        if (pmd_bad(*pmd))
                return true;
        pte = pte_offset_kernel(pmd, addr);
        return !pte_none(*pte);
}

static int __meminit kasan_mem_notifier(struct notifier_block *nb,
                        unsigned long action, void *data)
{
        struct memory_notify *mem_data = data;
        unsigned long nr_shadow_pages, start_kaddr, shadow_start;
        unsigned long shadow_end, shadow_size;

        nr_shadow_pages = mem_data->nr_pages >> KASAN_SHADOW_SCALE_SHIFT;
        start_kaddr = (unsigned long)pfn_to_kaddr(mem_data->start_pfn);
        shadow_start = (unsigned long)kasan_mem_to_shadow((void *)start_kaddr);
        shadow_size = nr_shadow_pages << PAGE_SHIFT;
        shadow_end = shadow_start + shadow_size;

        if (WARN_ON(mem_data->nr_pages % KASAN_SHADOW_SCALE_SIZE) ||
                WARN_ON(start_kaddr % (KASAN_SHADOW_SCALE_SIZE << PAGE_SHIFT)))
                return NOTIFY_BAD;

        switch (action) {
        case MEM_GOING_ONLINE: {
                void *ret;

                /*
                 * If shadow is mapped already than it must have been mapped
                 * during the boot. This could happen if we onlining previously
                 * offlined memory.
                 */
                if (shadow_mapped(shadow_start))
                        return NOTIFY_OK;

                ret = __vmalloc_node_range(shadow_size, PAGE_SIZE, shadow_start,
                                        shadow_end, GFP_KERNEL,
                                        PAGE_KERNEL, VM_NO_GUARD,
                                        pfn_to_nid(mem_data->start_pfn),
                                        __builtin_return_address(0));
                if (!ret)
                        return NOTIFY_BAD;

                kmemleak_ignore(ret);
                return NOTIFY_OK;
        }
        case MEM_CANCEL_ONLINE:
        case MEM_OFFLINE: {
                struct vm_struct *vm;

                /*
                 * shadow_start was either mapped during boot by kasan_init()
                 * or during memory online by __vmalloc_node_range().
                 * In the latter case we can use vfree() to free shadow.
                 * Non-NULL result of the find_vm_area() will tell us if
                 * that was the second case.
                 *
                 * Currently it's not possible to free shadow mapped
                 * during boot by kasan_init(). It's because the code
                 * to do that hasn't been written yet. So we'll just
                 * leak the memory.
                 */
                vm = find_vm_area((void *)shadow_start);
                if (vm)
                        vfree((void *)shadow_start);
        }
        }

        return NOTIFY_OK;
}

static int __init kasan_memhotplug_init(void)
{
        hotplug_memory_notifier(kasan_mem_notifier, 0);

        return 0;
}

core_initcall(kasan_memhotplug_init);
#endif

#ifdef CONFIG_KASAN_VMALLOC
static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
                                      void *unused)
{
        unsigned long page;
        pte_t pte;

        if (likely(!pte_none(*ptep)))
                return 0;

        page = __get_free_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        memset((void *)page, KASAN_VMALLOC_INVALID, PAGE_SIZE);
        pte = pfn_pte(PFN_DOWN(__pa(page)), PAGE_KERNEL);

        spin_lock(&init_mm.page_table_lock);
        if (likely(pte_none(*ptep))) {
                set_pte_at(&init_mm, addr, ptep, pte);
                page = 0;
        }
        spin_unlock(&init_mm.page_table_lock);
        if (page)
                free_page(page);
        return 0;
}

int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
{
        unsigned long shadow_start, shadow_end;
        int ret;

        if (!is_vmalloc_or_module_addr((void *)addr))
                return 0;

        shadow_start = (unsigned long)kasan_mem_to_shadow((void *)addr);
        shadow_start = ALIGN_DOWN(shadow_start, PAGE_SIZE);
        shadow_end = (unsigned long)kasan_mem_to_shadow((void *)addr + size);
        shadow_end = ALIGN(shadow_end, PAGE_SIZE);

        ret = apply_to_page_range(&init_mm, shadow_start,
                                  shadow_end - shadow_start,
                                  kasan_populate_vmalloc_pte, NULL);
        if (ret)
                return ret;

        flush_cache_vmap(shadow_start, shadow_end);

        /*
         * We need to be careful about inter-cpu effects here. Consider:
         *
         *   CPU#0                                CPU#1
         * WRITE_ONCE(p, vmalloc(100));         while (x = READ_ONCE(p)) ;
         *                                      p[99] = 1;
         *
         * With compiler instrumentation, that ends up looking like this:
         *
         *   CPU#0                                CPU#1
         * // vmalloc() allocates memory
         * // let a = area->addr
         * // we reach kasan_populate_vmalloc
         * // and call kasan_unpoison_shadow:
         * STORE shadow(a), unpoison_val
         * ...
         * STORE shadow(a+99), unpoison_val     x = LOAD p
         * // rest of vmalloc process           <data dependency>
         * STORE p, a                           LOAD shadow(x+99)
         *
         * If there is no barrier between the end of unpoisioning the shadow
         * and the store of the result to p, the stores could be committed
         * in a different order by CPU#0, and CPU#1 could erroneously observe
         * poison in the shadow.
         *
         * We need some sort of barrier between the stores.
         *
         * In the vmalloc() case, this is provided by a smp_wmb() in
         * clear_vm_uninitialized_flag(). In the per-cpu allocator and in
         * get_vm_area() and friends, the caller gets shadow allocated but
         * doesn't have any pages mapped into the virtual address space that
         * has been reserved. Mapping those pages in will involve taking and
         * releasing a page-table lock, which will provide the barrier.
         */

        return 0;
}

/*
 * Poison the shadow for a vmalloc region. Called as part of the
 * freeing process at the time the region is freed.
 */
void kasan_poison_vmalloc(const void *start, unsigned long size)
{
        if (!is_vmalloc_or_module_addr(start))
                return;

        size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
        kasan_poison_shadow(start, size, KASAN_VMALLOC_INVALID);
}

void kasan_unpoison_vmalloc(const void *start, unsigned long size)
{
        if (!is_vmalloc_or_module_addr(start))
                return;

        kasan_unpoison_shadow(start, size);
}

static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
                                        void *unused)
{
        unsigned long page;

        page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT);

        spin_lock(&init_mm.page_table_lock);

        if (likely(!pte_none(*ptep))) {
                pte_clear(&init_mm, addr, ptep);
                free_page(page);
        }
        spin_unlock(&init_mm.page_table_lock);

        return 0;
}

/*
 * Release the backing for the vmalloc region [start, end), which
 * lies within the free region [free_region_start, free_region_end).
 *
 * This can be run lazily, long after the region was freed. It runs
 * under vmap_area_lock, so it's not safe to interact with the vmalloc/vmap
 * infrastructure.
 *
 * How does this work?
 * -------------------
 *
 * We have a region that is page aligned, labelled as A.
 * That might not map onto the shadow in a way that is page-aligned:
 *
 *                    start                     end
 *                    v                         v
 * |????????|????????|AAAAAAAA|AA....AA|AAAAAAAA|????????| < vmalloc
 *  -------- -------- --------          -------- --------
 *      |        |       |                 |        |
 *      |        |       |         /-------/        |
 *      \-------\|/------/         |/---------------/
 *              |||                ||
 *             |??AAAAAA|AAAAAAAA|AA??????|                < shadow
 *                 (1)      (2)      (3)
 *
 * First we align the start upwards and the end downwards, so that the
 * shadow of the region aligns with shadow page boundaries. In the
 * example, this gives us the shadow page (2). This is the shadow entirely
 * covered by this allocation.
 *
 * Then we have the tricky bits. We want to know if we can free the
 * partially covered shadow pages - (1) and (3) in the example. For this,
 * we are given the start and end of the free region that contains this
 * allocation. Extending our previous example, we could have:
 *
 *  free_region_start                                    free_region_end
 *  |                 start                     end      |
 *  v                 v                         v        v
 * |FFFFFFFF|FFFFFFFF|AAAAAAAA|AA....AA|AAAAAAAA|FFFFFFFF| < vmalloc
 *  -------- -------- --------          -------- --------
 *      |        |       |                 |        |
 *      |        |       |         /-------/        |
 *      \-------\|/------/         |/---------------/
 *              |||                ||
 *             |FFAAAAAA|AAAAAAAA|AAF?????|                < shadow
 *                 (1)      (2)      (3)
 *
 * Once again, we align the start of the free region up, and the end of
 * the free region down so that the shadow is page aligned. So we can free
 * page (1) - we know no allocation currently uses anything in that page,
 * because all of it is in the vmalloc free region. But we cannot free
 * page (3), because we can't be sure that the rest of it is unused.
 *
 * We only consider pages that contain part of the original region for
 * freeing: we don't try to free other pages from the free region or we'd
 * end up trying to free huge chunks of virtual address space.
 *
 * Concurrency
 * -----------
 *
 * How do we know that we're not freeing a page that is simultaneously
 * being used for a fresh allocation in kasan_populate_vmalloc(_pte)?
 *
 * We _can_ have kasan_release_vmalloc and kasan_populate_vmalloc running
 * at the same time. While we run under free_vmap_area_lock, the population
 * code does not.
 *
 * free_vmap_area_lock instead operates to ensure that the larger range
 * [free_region_start, free_region_end) is safe: because __alloc_vmap_area and
 * the per-cpu region-finding algorithm both run under free_vmap_area_lock,
 * no space identified as free will become used while we are running. This
 * means that so long as we are careful with alignment and only free shadow
 * pages entirely covered by the free region, we will not run in to any
 * trouble - any simultaneous allocations will be for disjoint regions.
 */
void kasan_release_vmalloc(unsigned long start, unsigned long end,
                           unsigned long free_region_start,
                           unsigned long free_region_end)
{
        void *shadow_start, *shadow_end;
        unsigned long region_start, region_end;
        unsigned long size;

        region_start = ALIGN(start, PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
        region_end = ALIGN_DOWN(end, PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);

        free_region_start = ALIGN(free_region_start,
                                  PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);

        if (start != region_start &&
            free_region_start < region_start)
                region_start -= PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE;

        free_region_end = ALIGN_DOWN(free_region_end,
                                     PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);

        if (end != region_end &&
            free_region_end > region_end)
                region_end += PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE;

        shadow_start = kasan_mem_to_shadow((void *)region_start);
        shadow_end = kasan_mem_to_shadow((void *)region_end);

        if (shadow_end > shadow_start) {
                size = shadow_end - shadow_start;
                apply_to_existing_page_range(&init_mm,
                                             (unsigned long)shadow_start,
                                             size, kasan_depopulate_vmalloc_pte,
                                             NULL);
                flush_tlb_kernel_range((unsigned long)shadow_start,
                                       (unsigned long)shadow_end);
        }
}
#endif