Add basic tests for the kpkeys_hardened_pgtables feature: try to perform a direct write to kernel and user page table entries and ensure it fails.
Signed-off-by: Kevin Brodsky <[email protected]> --- mm/Makefile | 1 + mm/tests/kpkeys_hardened_pgtables_kunit.c | 106 ++++++++++++++++++++++ security/Kconfig.hardening | 12 +++ 3 files changed, 119 insertions(+) create mode 100644 mm/tests/kpkeys_hardened_pgtables_kunit.c diff --git a/mm/Makefile b/mm/Makefile index 10848df0ca85..b1e6cf7f753c 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -148,3 +148,4 @@ obj-$(CONFIG_EXECMEM) += execmem.o obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o obj-$(CONFIG_PT_RECLAIM) += pt_reclaim.o obj-$(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..3d916f0719d0 --- /dev/null +++ b/mm/tests/kpkeys_hardened_pgtables_kunit.c @@ -0,0 +1,106 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include <kunit/test.h> +#include <linux/mman.h> +#include <linux/pgtable.h> +#include <linux/vmalloc.h> + +KUNIT_DEFINE_ACTION_WRAPPER(vfree_wrapper, vfree, const void *); + +static inline 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); +} + +static void write_linear_map_pte(struct kunit *test) +{ + pte_t *ptep; + pte_t pte; + int ret; + + if (!arch_kpkeys_enabled()) + kunit_skip(test, "kpkeys are not supported"); + + /* + * The choice of address is mostly arbitrary - we just need something + * that is PTE-mapped, such as a global variable. + */ + ptep = get_kernel_pte((unsigned long)&init_mm); + KUNIT_ASSERT_NOT_NULL_MSG(test, ptep, "Failed to get PTE"); + + pte = ptep_get(ptep); + pte = set_pte_bit(pte, __pgprot(PTE_WRITE)); + ret = copy_to_kernel_nofault(ptep, &pte, sizeof(pte)); + KUNIT_EXPECT_EQ_MSG(test, ret, -EFAULT, + "Direct PTE write wasn't prevented"); +} + +static void write_kernel_vmalloc_pte(struct kunit *test) +{ + void *mem; + pte_t *ptep; + pte_t pte; + 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); + + ptep = get_kernel_pte((unsigned long)mem); + KUNIT_ASSERT_NOT_NULL_MSG(test, ptep, "Failed to get PTE"); + + pte = ptep_get(ptep); + pte = set_pte_bit(pte, __pgprot(PTE_WRITE)); + ret = copy_to_kernel_nofault(ptep, &pte, sizeof(pte)); + KUNIT_EXPECT_EQ_MSG(test, ret, -EFAULT, + "Direct PTE write wasn't prevented"); +} + +static void write_user_pmd(struct kunit *test) +{ + pmd_t *pmdp; + pmd_t pmd; + unsigned long uaddr; + int ret; + + 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"); + + pmd = pmdp_get(pmdp); + pmd = set_pmd_bit(pmd, __pgprot(PROT_SECT_NORMAL)); + ret = copy_to_kernel_nofault(pmdp, &pmd, sizeof(pmd)); + KUNIT_EXPECT_EQ_MSG(test, ret, -EFAULT, + "Direct PMD write wasn't prevented"); +} + +static struct kunit_case kpkeys_hardened_pgtables_test_cases[] = { + KUNIT_CASE(write_linear_map_pte), + KUNIT_CASE(write_kernel_vmalloc_pte), + KUNIT_CASE(write_user_pmd), + {} +}; + +static struct kunit_suite kpkeys_hardened_pgtables_test_suite = { + .name = "Hardened pgtables using kpkeys", + .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 41b7530530b7..653663008096 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -277,6 +277,18 @@ config KPKEYS_HARDENED_PGTABLES This option has no effect if the system does not support kernel pkeys. +config KPKEYS_HARDENED_PGTABLES_KUNIT_TEST + tristate "KUnit tests for kpkeys_hardened_pgtables" if !KUNIT_ALL_TESTS + depends on KPKEYS_HARDENED_PGTABLES + depends on KUNIT + 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 -- 2.47.0
