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t=1779794326; bh=hwcv2gonPHpgCT0f3+/I1m85tJYegiKdKnPZStVnGxs=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=F/U4Y59a//xfdzb3biidGRmmpns10SE1ABekJ1J4jBiRAORO4vXAkPRA3/AAh9yAK 16MYenua0OdnWEFug60TeFZoFPQ2Wdg12gsu3NuBqUCVkYM4OFvI5lPdZzFvBE6bTD Zhhtzjx6g1w/0VU/RtPAKFo6NY8lH/PQ+LNtEB88= From: Kevin Brodsky Date: Tue, 26 May 2026 12:16:10 +0100 Subject: [PATCH RFC v8 21/24] arm64: kpkeys: Guard page table writes MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260526-kpkeys-v8-21-eaaacdacc67c@arm.com> References: <20260526-kpkeys-v8-0-eaaacdacc67c@arm.com> In-Reply-To: <20260526-kpkeys-v8-0-eaaacdacc67c@arm.com> To: linux-hardening@vger.kernel.org Cc: Kevin Brodsky , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , "David Hildenbrand (Arm)" , Ira Weiny , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , Quentin Perret , Rick Edgecombe , Ryan Roberts , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org, Lorenzo Stoakes , Thomas Gleixner X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1779794212; l=4674; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=hwcv2gonPHpgCT0f3+/I1m85tJYegiKdKnPZStVnGxs=; b=acbni5FydzqysJ5dMgbsdAlXZrSXrjGZ9fILV417IMyC2z6ykw6ftEdeixBWE0s1kBd43a8Bh z9+CKJx/qiKCD3vFU+glse8yHgGm7Ws8vxmjz/JAEeXKgGZIBaPyBh+ X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= X-Rspamd-Server: rspam11 X-Stat-Signature: y7sp4ynq6rdoawzyqt6a8spzbmtsin5a X-Rspamd-Queue-Id: 9C7B1C0007 X-Rspam-User: X-HE-Tag: 1779794327-989592 X-HE-Meta: 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 vF7r+cQo aAtR+LHkchljXTMy/ti2AoF7hzX1AKhegGxYeV5vvGGBfHiFhLzOe+aUz6gsKijw/DDa+BJwS4uebP2iIopfB/BwqgIgOR9hlBeuF/h+0JYBssdw7R5pJVkEWP+H+s2FdOGpGms6AH0x0/vfuEOxb5KdroFQL38Mwh3m61n3Ud0ATCuMidHfmpQRa7GFRlBpDiU1sqjSx/La458SHcMpLkRG7RaZYgz09qlM1r0f7iISomqzsUimcSZlXE+qhXIFZ9Ebzj1a/E2fdofHfyC+oc+VsQSVYlAFeJpG6 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When CONFIG_KPKEYS_HARDENED_PGTABLES is enabled, page tables (both user and kernel) are mapped with a privileged pkey in the linear mapping. As a result, they can only be written in a privileged kpkeys context. Introduce a kpkeys guard that sets POR_EL1 appropriately to allow writing to page tables, and use this guard wherever necessary. The scope is kept as small as possible, so that POR_EL1 is quickly reset to its default value. Where atomics are involved, the guard's scope encompasses the whole loop to avoid switching POR_EL1 unnecessarily. This patch is a no-op if CONFIG_KPKEYS_HARDENED_PGTABLES is disabled (default). Signed-off-by: Kevin Brodsky --- arch/arm64/include/asm/pgtable.h | 22 +++++++++++++++++++++- arch/arm64/mm/fault.c | 17 ++++++++++------- 2 files changed, 31 insertions(+), 8 deletions(-) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 4dfa42b7d053..20072f32677d 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -39,6 +39,14 @@ #include #include #include +#include + +#ifdef CONFIG_KPKEYS_HARDENED_PGTABLES +KPKEYS_GUARD_COND(kpkeys_hardened_pgtables, KPKEYS_CTX_PGTABLES, + kpkeys_hardened_pgtables_enabled()) +#else +KPKEYS_GUARD_NOOP(kpkeys_hardened_pgtables) +#endif static inline void emit_pte_barriers(void) { @@ -359,6 +367,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte) static inline void __set_pte_nosync(pte_t *ptep, pte_t pte) { + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*ptep, pte); } @@ -830,6 +839,7 @@ static inline void set_pmd(pmd_t *pmdp, pmd_t pmd) } #endif /* __PAGETABLE_PMD_FOLDED */ + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pmdp, pmd); if (pmd_valid(pmd)) @@ -894,6 +904,7 @@ static inline void set_pud(pud_t *pudp, pud_t pud) return; } + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pudp, pud); if (pud_valid(pud)) @@ -975,6 +986,7 @@ static inline void set_p4d(p4d_t *p4dp, p4d_t p4d) return; } + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*p4dp, p4d); queue_pte_barriers(); } @@ -1103,6 +1115,7 @@ static inline void set_pgd(pgd_t *pgdp, pgd_t pgd) return; } + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pgdp, pgd); queue_pte_barriers(); } @@ -1307,6 +1320,7 @@ static inline bool __ptep_test_and_clear_young(struct vm_area_struct *vma, { pte_t old_pte, pte; + guard(kpkeys_hardened_pgtables)(); pte = __ptep_get(ptep); do { old_pte = pte; @@ -1354,7 +1368,10 @@ static inline pte_t __ptep_get_and_clear_anysz(struct mm_struct *mm, pte_t *ptep, unsigned long pgsize) { - pte_t pte = __pte(xchg_relaxed(&pte_val(*ptep), 0)); + pte_t pte; + + scoped_guard(kpkeys_hardened_pgtables) + pte = __pte(xchg_relaxed(&pte_val(*ptep), 0)); switch (pgsize) { case PAGE_SIZE: @@ -1427,6 +1444,7 @@ static inline void ___ptep_set_wrprotect(struct mm_struct *mm, { pte_t old_pte; + guard(kpkeys_hardened_pgtables)(); do { old_pte = pte; pte = pte_wrprotect(pte); @@ -1460,6 +1478,7 @@ static inline void __clear_young_dirty_pte(struct vm_area_struct *vma, { pte_t old_pte; + guard(kpkeys_hardened_pgtables)(); do { old_pte = pte; @@ -1507,6 +1526,7 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp, pmd_t pmd) { page_table_check_pmd_set(vma->vm_mm, address, pmdp, pmd); + guard(kpkeys_hardened_pgtables)(); return __pmd(xchg_relaxed(&pmd_val(*pmdp), pmd_val(pmd))); } #endif diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 739800835920..35f9b702f87d 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -227,13 +227,16 @@ int __ptep_set_access_flags_anysz(struct vm_area_struct *vma, */ pte_val(entry) ^= PTE_RDONLY; pteval = pte_val(pte); - do { - old_pteval = pteval; - pteval ^= PTE_RDONLY; - pteval |= pte_val(entry); - pteval ^= PTE_RDONLY; - pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, pteval); - } while (pteval != old_pteval); + scoped_guard(kpkeys_hardened_pgtables) { + do { + old_pteval = pteval; + pteval ^= PTE_RDONLY; + pteval |= pte_val(entry); + pteval ^= PTE_RDONLY; + pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, + pteval); + } while (pteval != old_pteval); + } /* * Invalidate the local stale read-only entry. Remote stale entries -- 2.51.2