linux-kernel - [RFC PATCH v2 15/15] mm: Add basic tests for kpkeys_hardened

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250108103250.3188419-16-kevin.brodsky@arm.com>
Date: Wed,  8 Jan 2025 10:32:50 +0000
From: Kevin Brodsky <kevin.brodsky@....com>
To: linux-hardening@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Kevin Brodsky <kevin.brodsky@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mark Brown <broonie@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Jann Horn <jannh@...gle.com>,
	Jeff Xu <jeffxu@...omium.org>,
	Joey Gouly <joey.gouly@....com>,
	Kees Cook <kees@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Andy Lutomirski <luto@...nel.org>,
	Marc Zyngier <maz@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Pierre Langlois <pierre.langlois@....com>,
	Quentin Perret <qperret@...gle.com>,
	"Mike Rapoport (IBM)" <rppt@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Qi Zheng <zhengqi.arch@...edance.com>,
	linux-arm-kernel@...ts.infradead.org,
	x86@...nel.org
Subject: [RFC PATCH v2 15/15] mm: Add basic tests for kpkeys_hardened_pgtables

Add basic tests for the kpkeys_hardened_pgtables feature: try to
perform a direct write to some kernel and user page table entry and
ensure it fails.

Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 mm/Makefile                        |  1 +
 mm/kpkeys_hardened_pgtables_test.c | 72 ++++++++++++++++++++++++++++++
 security/Kconfig.hardening         | 12 +++++
 3 files changed, 85 insertions(+)
 create mode 100644 mm/kpkeys_hardened_pgtables_test.c

diff --git a/mm/Makefile b/mm/Makefile
index 130691364172..f7263b7f45b8 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_TEST) += kpkeys_hardened_pgtables_test.o
diff --git a/mm/kpkeys_hardened_pgtables_test.c b/mm/kpkeys_hardened_pgtables_test.c
new file mode 100644
index 000000000000..86d862d43bea
--- /dev/null
+++ b/mm/kpkeys_hardened_pgtables_test.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <kunit/test.h>
+#include <linux/pgtable.h>
+#include <linux/mman.h>
+
+static void write_kernel_pte(struct kunit *test)
+{
+	pte_t *ptep;
+	pte_t pte;
+	int ret;
+
+	/*
+	 * The choice of address is mostly arbitrary - we just need a page
+	 * that is definitely mapped, such as the current function.
+	 */
+	ptep = virt_to_kpte((unsigned long)&write_kernel_pte);
+	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;
+
+	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 int kpkeys_hardened_pgtables_suite_init(struct kunit_suite *suite)
+{
+	if (!arch_kpkeys_enabled()) {
+		pr_err("Cannot run kpkeys_hardened_pgtables tests: kpkeys are not supported\n");
+		return 1;
+	}
+
+	return 0;
+}
+
+static struct kunit_case kpkeys_hardened_pgtables_test_cases[] = {
+	KUNIT_CASE(write_kernel_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,
+	.suite_init = kpkeys_hardened_pgtables_suite_init,
+};
+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 95f93f1d4055..8bc5d7235f6d 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -312,6 +312,18 @@ config KPKEYS_HARDENED_PGTABLES
 	  This option has no effect if the system does not support
 	  kernel pkeys.
 
+config KPKEYS_HARDENED_PGTABLES_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