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Multiple cases are considered for kernel page tables, as early page tables are allocated and/or protected in a different way. The tests are builtin (cannot be built as a module) because they refer to multiple symbols that are not exported (e.g. copy_to_kernel_nofault()). Signed-off-by: Kevin Brodsky --- mm/Makefile | 1 + mm/tests/kpkeys_hardened_pgtables_kunit.c | 202 ++++++++++++++++++++++ security/Kconfig.hardening | 12 ++ 3 files changed, 215 insertions(+) create mode 100644 mm/tests/kpkeys_hardened_pgtables_kunit.c diff --git a/mm/Makefile b/mm/Makefile index 7603e6051afa..9ebdbaa696b2 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -151,3 +151,4 @@ obj-$(CONFIG_EXECMEM) += execmem.o obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o obj-$(CONFIG_LAZY_MMU_MODE_KUNIT_TEST) += tests/lazy_mmu_mode_kunit.o obj-$(CONFIG_KPKEYS_HARDENED_PGTABLES) += kpkeys_hardened_pgtables.o +obj-$(CONFIG_KPKEYS_HARDENED_PGTABLES_KUNIT_TEST) += tests/kpkeys_hardened_pgtables_kunit.o diff --git a/mm/tests/kpkeys_hardened_pgtables_kunit.c b/mm/tests/kpkeys_hardened_pgtables_kunit.c new file mode 100644 index 000000000000..fa11fcd7abde --- /dev/null +++ b/mm/tests/kpkeys_hardened_pgtables_kunit.c @@ -0,0 +1,202 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include +#include +#include +#include +#include + +#ifdef CONFIG_ARM64 +#include +#endif + +static void free_page_wrapper(void *ctx) +{ + __free_page((struct page *)ctx); +} + +KUNIT_DEFINE_ACTION_WRAPPER(vfree_wrapper, vfree, const void *); + +static pud_t *pud_off_k(unsigned long va) +{ + return pud_offset(p4d_offset(pgd_offset_k(va), va), va); +} + +static pte_t *get_kernel_pte(unsigned long addr) +{ + pmd_t *pmdp = pmd_off_k(addr); + + if (!pmdp || pmd_leaf(*pmdp)) + return NULL; + + return pte_offset_kernel(pmdp, addr); +} + +#define write_pgtable(type, ptr) do { \ + type##_t val; \ + int ret; \ + \ + pr_debug("%s: writing to "#type" at %px\n", __func__, (ptr)); \ + \ + val = type##p_get(ptr); \ + ret = copy_to_kernel_nofault(ptr, &val, sizeof(val)); \ + KUNIT_EXPECT_EQ_MSG(test, ret, -EFAULT, \ + "Direct "#type" write wasn't prevented"); \ +} while (0) + +/* + * Try to write linear map page tables, at every level. This is worthwhile + * because those page table pages are obtained from different allocators: + * + * - Static memory (part of the kernel image) for PGD + * - memblock for PUD and possibly PMD/PTE + * - pagetable_alloc() (buddy allocator) for PMD/PTE if large block mappings are + * used and the linear map is split after being created + */ +static void write_direct_map_pgtables(struct kunit *test) +{ + struct page *page; + unsigned long addr; + pgd_t *pgdp; + p4d_t *p4dp; + pud_t *pudp; + pmd_t *pmdp; + pte_t *ptep; + int ret; + + if (!arch_kpkeys_enabled()) + kunit_skip(test, "kpkeys are not supported"); + + page = alloc_page(GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, page); + ret = kunit_add_action_or_reset(test, free_page_wrapper, page); + KUNIT_ASSERT_EQ(test, ret, 0); + + /* Ensure page is PTE-mapped (splitting the linear map if necessary) */ + ret = set_direct_map_invalid_noflush(page); + KUNIT_ASSERT_EQ(test, ret, 0); + ret = set_direct_map_default_noflush(page); + KUNIT_ASSERT_EQ(test, ret, 0); + + addr = (unsigned long)page_address(page); + + pgdp = pgd_offset_k(addr); + KUNIT_ASSERT_NOT_NULL_MSG(test, pgdp, "Failed to get PGD"); + /* + * swapper_pg_dir is still writable at this stage, so don't check it. + * It is not protected by kpkeys_hardened_pgtables because it should be + * made read-only by mark_rodata_ro(). However since these + * KUnit tests are builtin, they are run before mark_rodata_ro() is + * called. + */ + + p4dp = p4d_offset(pgdp, addr); + KUNIT_ASSERT_NOT_NULL_MSG(test, p4dp, "Failed to get P4D"); + /* Not checked; same rationale as PGD in case P4D is folded */ + + pudp = pud_offset(p4dp, addr); + KUNIT_ASSERT_NOT_NULL_MSG(test, pudp, "Failed to get PUD"); + write_pgtable(pud, pudp); + + pmdp = pmd_offset(pudp, addr); + KUNIT_ASSERT_NOT_NULL_MSG(test, pmdp, "Failed to get PMD"); + write_pgtable(pmd, pmdp); + + ptep = pte_offset_kernel(pmdp, addr); + KUNIT_ASSERT_NOT_NULL_MSG(test, ptep, "Failed to get PTE"); + write_pgtable(pte, ptep); +} + +/* Worth checking since the kernel image is mapped with static page tables */ +static void write_kernel_image_pud(struct kunit *test) +{ + pud_t *pudp; + + if (!arch_kpkeys_enabled()) + kunit_skip(test, "kpkeys are not supported"); + + /* The kernel is probably block-mapped, check the PUD to be safe */ + pudp = pud_off_k((unsigned long)&init_mm); + KUNIT_ASSERT_NOT_NULL_MSG(test, pudp, "Failed to get PUD"); + + write_pgtable(pud, pudp); +} + +static void write_kernel_vmalloc_pte(struct kunit *test) +{ + void *mem; + pte_t *ptep; + int ret; + + if (!arch_kpkeys_enabled()) + kunit_skip(test, "kpkeys are not supported"); + + mem = vmalloc(PAGE_SIZE); + KUNIT_ASSERT_NOT_NULL(test, mem); + ret = kunit_add_action_or_reset(test, vfree_wrapper, mem); + KUNIT_ASSERT_EQ(test, ret, 0); + + /* vmalloc() without VM_ALLOW_HUGE_VMAP is PTE-mapped */ + ptep = get_kernel_pte((unsigned long)mem); + KUNIT_ASSERT_NOT_NULL_MSG(test, ptep, "Failed to get PTE"); + + write_pgtable(pte, ptep); +} + +#ifdef CONFIG_ARM64 +static void write_early_kernel_vmap_pte(struct kunit *test) +{ + pte_t *ptep; + + if (!arch_kpkeys_enabled()) + kunit_skip(test, "kpkeys are not supported"); + + /* + * When block mappings are used, the IRQ stacks are allocated before + * set_memory_pkey() is available - the pkey is set later by + * kpkeys_hardened_pgtables_init_late() + */ + ptep = get_kernel_pte((unsigned long)raw_cpu_read(irq_stack_ptr)); + KUNIT_ASSERT_NOT_NULL_MSG(test, ptep, "Failed to get PTE"); + + write_pgtable(pte, ptep); +} +#endif + +static void write_user_pmd(struct kunit *test) +{ + pmd_t *pmdp; + unsigned long uaddr; + + if (!arch_kpkeys_enabled()) + kunit_skip(test, "kpkeys are not supported"); + + uaddr = kunit_vm_mmap(test, NULL, 0, PAGE_SIZE, PROT_READ, + MAP_ANONYMOUS | MAP_PRIVATE | MAP_POPULATE, 0); + KUNIT_ASSERT_NE_MSG(test, uaddr, 0, "Could not create userspace mm"); + + /* We passed MAP_POPULATE so a PMD should already be allocated */ + pmdp = pmd_off(current->mm, uaddr); + KUNIT_ASSERT_NOT_NULL_MSG(test, pmdp, "Failed to get PMD"); + + write_pgtable(pmd, pmdp); +} + +static struct kunit_case kpkeys_hardened_pgtables_test_cases[] = { + KUNIT_CASE(write_direct_map_pgtables), + KUNIT_CASE(write_kernel_image_pud), + KUNIT_CASE(write_kernel_vmalloc_pte), +#ifdef CONFIG_ARM64 + KUNIT_CASE(write_early_kernel_vmap_pte), +#endif + KUNIT_CASE(write_user_pmd), + {} +}; + +static struct kunit_suite kpkeys_hardened_pgtables_test_suite = { + .name = "kpkeys_hardened_pgtables", + .test_cases = kpkeys_hardened_pgtables_test_cases, +}; +kunit_test_suite(kpkeys_hardened_pgtables_test_suite); + +MODULE_DESCRIPTION("Tests for the kpkeys_hardened_pgtables feature"); +MODULE_LICENSE("GPL"); diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening index fdaf977d4626..48789f93e933 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -287,6 +287,18 @@ config KPKEYS_HARDENED_PGTABLES This option has no effect if the system does not support kernel pkeys. +config KPKEYS_HARDENED_PGTABLES_KUNIT_TEST + bool "KUnit tests for kpkeys_hardened_pgtables" if !KUNIT_ALL_TESTS + depends on KPKEYS_HARDENED_PGTABLES + depends on KUNIT=y + default KUNIT_ALL_TESTS + help + Enable this option to check that the kpkeys_hardened_pgtables feature + functions as intended, i.e. prevents arbitrary writes to user and + kernel page tables. + + If unsure, say N. + endmenu config CC_HAS_RANDSTRUCT -- 2.51.2