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