diff options
Diffstat (limited to 'mm/page_table_check.c')
| -rw-r--r-- | mm/page_table_check.c | 246 |
1 files changed, 246 insertions, 0 deletions
diff --git a/mm/page_table_check.c b/mm/page_table_check.c new file mode 100644 index 000000000..af69c3c8f --- /dev/null +++ b/mm/page_table_check.c @@ -0,0 +1,246 @@ +// 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); + } +} |