From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=217.140.110.172 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794240151; b=4zXC3GLoVpfrkVc5MnYp0of+UnIL/5gXzA/8aFroHLUuCeo9GR/BID0NbdxnooVRusxb K3S1O8VWjRtWJ0VHD7g+b3M/NEXhRASa/cmdEEpv7uWcmI+Yrxr/KPClz0OlQq6RvEswv RQlvNc9KN7AiUcbz86aohKK5CG0gEechHWhwGNPbKvrEFPfvkYtbL0cRnlFhBjnfhrb80 X/O+5phPaNELTuKI0IBP/H2a557/jrgqK/XJ0XpkN1DvlxGlpqUn410Dm2iPkjSim81nw hLNJ/QO2XDPooO6Tb5M1wLA0N2kdfgZn9gTP4k14TJvX/8kHzT5bfjzKIKAw1bMJiWg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794240151; h=DMARC-Filter:Received:Received:DKIM-Signature:From:Date:Subject: MIME-Version:Content-Type:Content-Transfer-Encoding:Message-Id: References:In-Reply-To:To:Cc:X-Mailer:X-Developer-Signature: X-Developer-Key; bh=KEIsFW9jH6gypon3gbKl/1F5oRxGR3xdBdmV6PMmfqQ=; b=SAU9Y3SPkUYSEelmdAarjk7Z7eGyTaTrqUZNM0DHkGqd/GQ/8q6L+RLjlN77D5ZG6iQM 0e5/9rTEqnMa93i8/PsxGOZni0e+FRje3c8L+8FO54efBoNTP8iZUR+dQpaqTNxT/xcDL UDfn4vzcZ0yVZ8DhP1vMhz/XghYuyjh9nYjrPrYt0PkK/MMr8vGUvmhHNdcPHUBmHuR6O Ha3vKllYDvcF9Or2clucNZXUTf8SIQM8TiCpy9iD2Sf2xrIGKlZe4IIq6tCMLkef3nsnA HH2wY5SjlQYgFfP+0mWDxVWLYZAyTEB7BMOAfWkq0huCjr/m+pHAJbM8qxOO8+Z8dPA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=iMDYvXpk; arc=none smtp.remote-ip=217.140.110.172 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 491BA606EE93; Mon, 9 Nov 2026 16:02:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 491BA606EE93 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=iMDYvXpk Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8B13A2F; Mon, 9 Nov 2026 08:02:26 -0800 (PST) Received: from localhost.localdomain (e123572-lin.cambridge.arm.com [10.2.208.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AE4A23F632; Mon, 9 Nov 2026 08:02:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1794240149; bh=whHNqvrgkNGDWhe3Qiyv8K8tTXQdyzS5DNMu5K3JCD8=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=iMDYvXpkelxJePBSzgn+i0+x2akbCd3CBRy4l7OFEcb2EjWv+m/azm068BZjkdudw YKEYwtuM+C3x9QW+Yc1qQptt5HFwSwubGdIKbovaVUgFYoQpjw2zhHxQOKfFxessjl qlyJJr2NTrOl02unsu0tYLesKm6upWccZeB/WIuI= From: Kevin Brodsky Date: Mon, 09 Nov 2026 15:58:47 +0000 Subject: [PATCH RFC v10 22/22] mm: Add basic tests for kpkeys_hardened_pgtables X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261109-kpkeys-v10-22-aa6c4d9603bc@arm.com> References: <20261109-kpkeys-v10-0-aa6c4d9603bc@arm.com> In-Reply-To: <20261109-kpkeys-v10-0-aa6c4d9603bc@arm.com> To: linux-hardening@vger.kernel.org Cc: Kevin Brodsky , Andrew Morton , Ard Biesheuvel , Andy Lutomirski , Catalin Marinas , Dave Hansen , "David Hildenbrand (Arm)" , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linu Cherian , Linus Walleij , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , =?utf-8?q?Pierre-Cl=C3=A9ment_Tosi?= , Quentin Perret , Rick Edgecombe , Ryan Roberts , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org, Ira Weiny , Lorenzo Stoakes , Thomas Gleixner X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=ed25519-sha256; t=1794240029; l=8244; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=whHNqvrgkNGDWhe3Qiyv8K8tTXQdyzS5DNMu5K3JCD8=; b=864d1s7mcMPTzdCv7ZDhpZX1q/RPNV085d42av0+370yfZpQDlIINNoHvAQ+w9IRHJ61oZ8JS 4f2IZ8ZwfhmA+1swOc3JPZECBbVL4jaLroXdU6aJWI3is9jZl7ZvBf2 X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= Add basic tests for the kpkeys_hardened_pgtables feature: try to perform direct writes to kernel and user page table entries and ensure they fail. 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()). Reviewed-by: Yeoreum Yun Signed-off-by: Kevin Brodsky --- mm/Makefile | 1 + mm/tests/kpkeys_hardened_pgtables_kunit.c | 200 ++++++++++++++++++++++++++++++ security/Kconfig.hardening | 12 ++ 3 files changed, 213 insertions(+) diff --git a/mm/Makefile b/mm/Makefile index 07b67eaa1b3b..4acdd3c58b46 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -150,3 +150,4 @@ obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o obj-$(CONFIG_LAZY_MMU_MODE_KUNIT_TEST) += tests/lazy_mmu_mode_kunit.o obj-$(CONFIG_MEM_ALLOC_PROFILING) += alloc_tag.o obj-$(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..b6e1eba0d9b9 --- /dev/null +++ b/mm/tests/kpkeys_hardened_pgtables_kunit.c @@ -0,0 +1,200 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include +#include +#include +#include +#include + +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 (!kpkeys_supported()) + 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, 1); + KUNIT_ASSERT_EQ(test, ret, 0); + ret = set_direct_map_default_noflush(page, 1); + 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"); + if (!mm_p4d_folded(&init_mm)) + write_pgtable(p4d, p4dp); + + pudp = pud_offset(p4dp, addr); + KUNIT_ASSERT_NOT_NULL_MSG(test, pudp, "Failed to get PUD"); + if (!mm_pud_folded(&init_mm)) + 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 (!kpkeys_supported()) + 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 (!kpkeys_supported()) + 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); +} + +static void write_vmemmap_pmd(struct kunit *test) +{ + struct page *page; + pmd_t *pmdp; + + if (!kpkeys_supported()) + kunit_skip(test, "kpkeys are not supported"); + + /* + * We just need the address of some struct page, so we can free the + * page right away. + */ + page = alloc_page(GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, page); + __free_page(page); + + /* vmemmap may use PMD block mappings */ + pmdp = pmd_off_k((unsigned long)page); + KUNIT_ASSERT_NOT_NULL_MSG(test, pmdp, "Failed to get PMD"); + write_pgtable(pmd, pmdp); +} + +static void write_user_pmd(struct kunit *test) +{ + pmd_t *pmdp; + unsigned long uaddr; + + if (!kpkeys_supported()) + 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), + KUNIT_CASE(write_vmemmap_pmd), + 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 9a6f50103482..af0f83e3a19c 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -283,6 +283,18 @@ 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 -- 2.56.0