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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2021, Google LLC.
* Pasha Tatashin <pasha.tatashin@soleen.com>
*/
#include <linux/mm.h>
#include <linux/page_table_check.h>
#undef pr_fmt
#define pr_fmt(fmt) "page_table_check: " fmt
struct page_table_check {
atomic_t anon_map_count;
atomic_t file_map_count;
};
static bool __page_table_check_enabled __initdata =
IS_ENABLED(CONFIG_PAGE_TABLE_CHECK_ENFORCED);
DEFINE_STATIC_KEY_TRUE(page_table_check_disabled);
EXPORT_SYMBOL(page_table_check_disabled);
static int __init early_page_table_check_param(char *buf)
{
if (!buf)
return -EINVAL;
if (strcmp(buf, "on") == 0)
__page_table_check_enabled = true;
else if (strcmp(buf, "off") == 0)
__page_table_check_enabled = false;
return 0;
}
early_param("page_table_check", early_page_table_check_param);
static bool __init need_page_table_check(void)
{
return __page_table_check_enabled;
}
static void __init init_page_table_check(void)
{
if (!__page_table_check_enabled)
return;
static_branch_disable(&page_table_check_disabled);
}
struct page_ext_operations page_table_check_ops = {
.size = sizeof(struct page_table_check),
.need = need_page_table_check,
.init = init_page_table_check,
};
static struct page_table_check *get_page_table_check(struct page_ext *page_ext)
{
BUG_ON(!page_ext);
return (void *)(page_ext) + page_table_check_ops.offset;
}
static inline bool pte_user_accessible_page(pte_t pte)
{
return (pte_val(pte) & _PAGE_PRESENT) && (pte_val(pte) & _PAGE_USER);
}
static inline bool pmd_user_accessible_page(pmd_t pmd)
{
return pmd_leaf(pmd) && (pmd_val(pmd) & _PAGE_PRESENT) &&
(pmd_val(pmd) & _PAGE_USER);
}
static inline bool pud_user_accessible_page(pud_t pud)
{
return pud_leaf(pud) && (pud_val(pud) & _PAGE_PRESENT) &&
(pud_val(pud) & _PAGE_USER);
}
/*
* An enty is removed from the page table, decrement the counters for that page
* verify that it is of correct type and counters do not become negative.
*/
static void page_table_check_clear(struct mm_struct *mm, unsigned long addr,
unsigned long pfn, unsigned long pgcnt)
{
struct page_ext *page_ext;
struct page *page;
bool anon;
int i;
if (!pfn_valid(pfn))
return;
page = pfn_to_page(pfn);
page_ext = lookup_page_ext(page);
anon = PageAnon(page);
for (i = 0; i < pgcnt; i++) {
struct page_table_check *ptc = get_page_table_check(page_ext);
if (anon) {
BUG_ON(atomic_read(&ptc->file_map_count));
BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0);
} else {
BUG_ON(atomic_read(&ptc->anon_map_count));
BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0);
}
page_ext = page_ext_next(page_ext);
}
}
/*
* A new enty is added to the page table, increment the counters for that page
* verify that it is of correct type and is not being mapped with a different
* type to a different process.
*/
static void page_table_check_set(struct mm_struct *mm, unsigned long addr,
unsigned long pfn, unsigned long pgcnt,
bool rw)
{
struct page_ext *page_ext;
struct page *page;
bool anon;
int i;
if (!pfn_valid(pfn))
return;
page = pfn_to_page(pfn);
page_ext = lookup_page_ext(page);
anon = PageAnon(page);
for (i = 0; i < pgcnt; i++) {
struct page_table_check *ptc = get_page_table_check(page_ext);
if (anon) {
BUG_ON(atomic_read(&ptc->file_map_count));
BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw);
} else {
BUG_ON(atomic_read(&ptc->anon_map_count));
BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0);
}
page_ext = page_ext_next(page_ext);
}
}
/*
* page is on free list, or is being allocated, verify that counters are zeroes
* crash if they are not.
*/
void __page_table_check_zero(struct page *page, unsigned int order)
{
struct page_ext *page_ext = lookup_page_ext(page);
int i;
BUG_ON(!page_ext);
for (i = 0; i < (1 << order); i++) {
struct page_table_check *ptc = get_page_table_check(page_ext);
BUG_ON(atomic_read(&ptc->anon_map_count));
BUG_ON(atomic_read(&ptc->file_map_count));
page_ext = page_ext_next(page_ext);
}
}
void __page_table_check_pte_clear(struct mm_struct *mm, unsigned long addr,
pte_t pte)
{
if (&init_mm == mm)
return;
if (pte_user_accessible_page(pte)) {
page_table_check_clear(mm, addr, pte_pfn(pte),
PAGE_SIZE >> PAGE_SHIFT);
}
}
EXPORT_SYMBOL(__page_table_check_pte_clear);
void __page_table_check_pmd_clear(struct mm_struct *mm, unsigned long addr,
pmd_t pmd)
{
if (&init_mm == mm)
return;
if (pmd_user_accessible_page(pmd)) {
page_table_check_clear(mm, addr, pmd_pfn(pmd),
PMD_PAGE_SIZE >> PAGE_SHIFT);
}
}
EXPORT_SYMBOL(__page_table_check_pmd_clear);
void __page_table_check_pud_clear(struct mm_struct *mm, unsigned long addr,
pud_t pud)
{
if (&init_mm == mm)
return;
if (pud_user_accessible_page(pud)) {
page_table_check_clear(mm, addr, pud_pfn(pud),
PUD_PAGE_SIZE >> PAGE_SHIFT);
}
}
EXPORT_SYMBOL(__page_table_check_pud_clear);
void __page_table_check_pte_set(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte)
{
pte_t old_pte;
if (&init_mm == mm)
return;
old_pte = *ptep;
if (pte_user_accessible_page(old_pte)) {
page_table_check_clear(mm, addr, pte_pfn(old_pte),
PAGE_SIZE >> PAGE_SHIFT);
}
if (pte_user_accessible_page(pte)) {
page_table_check_set(mm, addr, pte_pfn(pte),
PAGE_SIZE >> PAGE_SHIFT,
pte_write(pte));
}
}
EXPORT_SYMBOL(__page_table_check_pte_set);
void __page_table_check_pmd_set(struct mm_struct *mm, unsigned long addr,
pmd_t *pmdp, pmd_t pmd)
{
pmd_t old_pmd;
if (&init_mm == mm)
return;
old_pmd = *pmdp;
if (pmd_user_accessible_page(old_pmd)) {
page_table_check_clear(mm, addr, pmd_pfn(old_pmd),
PMD_PAGE_SIZE >> PAGE_SHIFT);
}
if (pmd_user_accessible_page(pmd)) {
page_table_check_set(mm, addr, pmd_pfn(pmd),
PMD_PAGE_SIZE >> PAGE_SHIFT,
pmd_write(pmd));
}
}
EXPORT_SYMBOL(__page_table_check_pmd_set);
void __page_table_check_pud_set(struct mm_struct *mm, unsigned long addr,
pud_t *pudp, pud_t pud)
{
pud_t old_pud;
if (&init_mm == mm)
return;
old_pud = *pudp;
if (pud_user_accessible_page(old_pud)) {
page_table_check_clear(mm, addr, pud_pfn(old_pud),
PUD_PAGE_SIZE >> PAGE_SHIFT);
}
if (pud_user_accessible_page(pud)) {
page_table_check_set(mm, addr, pud_pfn(pud),
PUD_PAGE_SIZE >> PAGE_SHIFT,
pud_write(pud));
}
}
EXPORT_SYMBOL(__page_table_check_pud_set);
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