// SPDX-License-Identifier: GPL-2.0 /* * Copyright (c) 2021, Google LLC. * Pasha Tatashin <pasha.tatashin@soleen.com> */ #include <linux/kstrtox.h> #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) { return kstrtobool(buf, &__page_table_check_enabled); } 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, .need_shared_flags = false, }; static struct page_table_check *get_page_table_check(struct page_ext *page_ext) { BUG_ON(!page_ext); return page_ext_data(page_ext, &page_table_check_ops); } /* * An entry 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(unsigned long pfn, unsigned long pgcnt) { struct page_ext *page_ext; struct page *page; unsigned long i; bool anon; if (!pfn_valid(pfn)) return; page = pfn_to_page(pfn); page_ext = page_ext_get(page); BUG_ON(PageSlab(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); } page_ext_put(page_ext); } /* * A new entry 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(unsigned long pfn, unsigned long pgcnt, bool rw) { struct page_ext *page_ext; struct page *page; unsigned long i; bool anon; if (!pfn_valid(pfn)) return; page = pfn_to_page(pfn); page_ext = page_ext_get(page); BUG_ON(PageSlab(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_ext_put(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; unsigned long i; BUG_ON(PageSlab(page)); page_ext = page_ext_get(page); BUG_ON(!page_ext); for (i = 0; i < (1ul << 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); } page_ext_put(page_ext); } void __page_table_check_pte_clear(struct mm_struct *mm, pte_t pte) { if (&init_mm == mm) return; if (pte_user_accessible_page(pte)) { page_table_check_clear(pte_pfn(pte), PAGE_SIZE >> PAGE_SHIFT); } } EXPORT_SYMBOL(__page_table_check_pte_clear); void __page_table_check_pmd_clear(struct mm_struct *mm, pmd_t pmd) { if (&init_mm == mm) return; if (pmd_user_accessible_page(pmd)) { page_table_check_clear(pmd_pfn(pmd), PMD_SIZE >> PAGE_SHIFT); } } EXPORT_SYMBOL(__page_table_check_pmd_clear); void __page_table_check_pud_clear(struct mm_struct *mm, pud_t pud) { if (&init_mm == mm) return; if (pud_user_accessible_page(pud)) { page_table_check_clear(pud_pfn(pud), PUD_SIZE >> PAGE_SHIFT); } } EXPORT_SYMBOL(__page_table_check_pud_clear); void __page_table_check_ptes_set(struct mm_struct *mm, pte_t *ptep, pte_t pte, unsigned int nr) { unsigned int i; if (&init_mm == mm) return; for (i = 0; i < nr; i++) __page_table_check_pte_clear(mm, ptep_get(ptep + i)); if (pte_user_accessible_page(pte)) page_table_check_set(pte_pfn(pte), nr, pte_write(pte)); } EXPORT_SYMBOL(__page_table_check_ptes_set); void __page_table_check_pmd_set(struct mm_struct *mm, pmd_t *pmdp, pmd_t pmd) { if (&init_mm == mm) return; __page_table_check_pmd_clear(mm, *pmdp); if (pmd_user_accessible_page(pmd)) { page_table_check_set(pmd_pfn(pmd), PMD_SIZE >> PAGE_SHIFT, pmd_write(pmd)); } } EXPORT_SYMBOL(__page_table_check_pmd_set); void __page_table_check_pud_set(struct mm_struct *mm, pud_t *pudp, pud_t pud) { if (&init_mm == mm) return; __page_table_check_pud_clear(mm, *pudp); if (pud_user_accessible_page(pud)) { page_table_check_set(pud_pfn(pud), PUD_SIZE >> PAGE_SHIFT, pud_write(pud)); } } EXPORT_SYMBOL(__page_table_check_pud_set); void __page_table_check_pte_clear_range(struct mm_struct *mm, unsigned long addr, pmd_t pmd) { if (&init_mm == mm) return; if (!pmd_bad(pmd) && !pmd_leaf(pmd)) { pte_t *ptep = pte_offset_map(&pmd, addr); unsigned long i; if (WARN_ON(!ptep)) return; for (i = 0; i < PTRS_PER_PTE; i++) { __page_table_check_pte_clear(mm, ptep_get(ptep)); addr += PAGE_SIZE; ptep++; } pte_unmap(ptep - PTRS_PER_PTE); } }