From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) by kanga.kvack.org (Postfix) with ESMTP id 94DFB6B5226 for ; Thu, 30 Aug 2018 10:43:46 -0400 (EDT) Received: by mail-pl1-f197.google.com with SMTP id d40-v6so4052464pla.14 for ; Thu, 30 Aug 2018 07:43:46 -0700 (PDT) Received: from mga01.intel.com (mga01.intel.com. [192.55.52.88]) by mx.google.com with ESMTPS id w13-v6si6403728pll.449.2018.08.30.07.43.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 Aug 2018 07:43:44 -0700 (PDT) From: Yu-cheng Yu Subject: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Date: Thu, 30 Aug 2018 07:38:52 -0700 Message-Id: <20180830143904.3168-13-yu-cheng.yu@intel.com> In-Reply-To: <20180830143904.3168-1-yu-cheng.yu@intel.com> References: <20180830143904.3168-1-yu-cheng.yu@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , "Ravi V. Shankar" , Vedvyas Shanbhogue Cc: Yu-cheng Yu When Shadow Stack is enabled, the read-only and PAGE_DIRTY_HW PTE setting is reserved only for the Shadow Stack. To track dirty of non-Shadow Stack read-only PTEs, we use PAGE_DIRTY_SW. Update ptep_set_wrprotect() and pmdp_set_wrprotect(). Signed-off-by: Yu-cheng Yu --- arch/x86/include/asm/pgtable.h | 42 ++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 4d50de77ea96..556ef258eeff 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1203,7 +1203,28 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm, static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr, pte_t *ptep) { + pte_t pte; + clear_bit(_PAGE_BIT_RW, (unsigned long *)&ptep->pte); + pte = *ptep; + + /* + * Some processors can start a write, but ending up seeing + * a read-only PTE by the time they get to the Dirty bit. + * In this case, they will set the Dirty bit, leaving a + * read-only, Dirty PTE which looks like a Shadow Stack PTE. + * + * However, this behavior has been improved and will not occur + * on processors supporting Shadow Stacks. Without this + * guarantee, a transition to a non-present PTE and flush the + * TLB would be needed. + * + * When change a writable PTE to read-only and if the PTE has + * _PAGE_DIRTY_HW set, we move that bit to _PAGE_DIRTY_SW so + * that the PTE is not a valid Shadow Stack PTE. + */ + pte = pte_move_flags(pte, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW); + set_pte_at(mm, addr, ptep, pte); } #define flush_tlb_fix_spurious_fault(vma, address) do { } while (0) @@ -1266,7 +1287,28 @@ static inline pud_t pudp_huge_get_and_clear(struct mm_struct *mm, static inline void pmdp_set_wrprotect(struct mm_struct *mm, unsigned long addr, pmd_t *pmdp) { + pmd_t pmd; + clear_bit(_PAGE_BIT_RW, (unsigned long *)pmdp); + pmd = *pmdp; + + /* + * Some processors can start a write, but ending up seeing + * a read-only PTE by the time they get to the Dirty bit. + * In this case, they will set the Dirty bit, leaving a + * read-only, Dirty PTE which looks like a Shadow Stack PTE. + * + * However, this behavior has been improved and will not occur + * on processors supporting Shadow Stacks. Without this + * guarantee, a transition to a non-present PTE and flush the + * TLB would be needed. + * + * When change a writable PTE to read-only and if the PTE has + * _PAGE_DIRTY_HW set, we move that bit to _PAGE_DIRTY_SW so + * that the PTE is not a valid Shadow Stack PTE. + */ + pmd = pmd_move_flags(pmd, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW); + set_pmd_at(mm, addr, pmdp, pmd); } #define pud_write pud_write -- 2.17.1