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[192.55.52.93]) by mx.google.com with ESMTPS id 31-v6si17386340plz.217.2018.07.10.15.31.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 10 Jul 2018 15:31:14 -0700 (PDT) Received-SPF: pass (google.com: domain of yu-cheng.yu@intel.com designates 192.55.52.93 as permitted sender) client-ip=192.55.52.93; Authentication-Results: mx.google.com; spf=pass (google.com: domain of yu-cheng.yu@intel.com designates 192.55.52.93 as permitted sender) smtp.mailfrom=yu-cheng.yu@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Jul 2018 15:31:13 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,335,1526367600"; d="scan'208";a="70305412" Received: from 2b52.sc.intel.com ([143.183.136.52]) by fmsmga004.fm.intel.com with ESMTP; 10 Jul 2018 15:31:13 -0700 From: Yu-cheng Yu 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 Subject: [RFC PATCH v2 13/27] mm: Handle shadow stack page fault Date: Tue, 10 Jul 2018 15:26:25 -0700 Message-Id: <20180710222639.8241-14-yu-cheng.yu@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20180710222639.8241-1-yu-cheng.yu@intel.com> References: <20180710222639.8241-1-yu-cheng.yu@intel.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP When a task does fork(), its shadow stack must be duplicated for the child. However, the child may not actually use all pages of of the copied shadow stack. This patch implements a flow that is similar to copy-on-write of an anonymous page, but for shadow stack memory. A shadow stack PTE needs to be RO and dirty. We use this dirty bit requirement to effect the copying of shadow stack pages. In copy_one_pte(), we clear the dirty bit from the shadow stack PTE. On the next shadow stack access to the PTE, a page fault occurs. At that time, we then copy/re-use the page and fix the PTE. Signed-off-by: Yu-cheng Yu --- mm/memory.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 7206a634270b..a2695dbc0418 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2453,7 +2453,13 @@ static inline void wp_page_reuse(struct vm_fault *vmf) flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte)); entry = pte_mkyoung(vmf->orig_pte); - entry = maybe_mkwrite(pte_mkdirty(entry), vma); + + if (is_shstk_mapping(vma->vm_flags)) + entry = pte_mkdirty_shstk(entry); + else + entry = pte_mkdirty(entry); + + entry = maybe_mkwrite(entry, vma); if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1)) update_mmu_cache(vma, vmf->address, vmf->pte); pte_unmap_unlock(vmf->pte, vmf->ptl); @@ -2526,7 +2532,11 @@ static int wp_page_copy(struct vm_fault *vmf) } flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte)); entry = mk_pte(new_page, vma->vm_page_prot); - entry = maybe_mkwrite(pte_mkdirty(entry), vma); + if (is_shstk_mapping(vma->vm_flags)) + entry = pte_mkdirty_shstk(entry); + else + entry = pte_mkdirty(entry); + entry = maybe_mkwrite(entry, vma); /* * Clear the pte entry and flush it first, before updating the * pte with the new entry. This will avoid a race condition @@ -3201,6 +3211,14 @@ static int do_anonymous_page(struct vm_fault *vmf) mem_cgroup_commit_charge(page, memcg, false, false); lru_cache_add_active_or_unevictable(page, vma); setpte: + /* + * If this is within a shadow stack mapping, mark + * the PTE dirty. We don't use pte_mkdirty(), + * because the PTE must have _PAGE_DIRTY_HW set. + */ + if (is_shstk_mapping(vma->vm_flags)) + entry = pte_mkdirty_shstk(entry); + set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry); /* No need to invalidate - it was non-present before */ @@ -3983,6 +4001,14 @@ static int handle_pte_fault(struct vm_fault *vmf) entry = vmf->orig_pte; if (unlikely(!pte_same(*vmf->pte, entry))) goto unlock; + + /* + * Shadow stack PTEs are copy-on-access, so do_wp_page() + * handling on them no matter if we have write fault or not. + */ + if (is_shstk_mapping(vmf->vma->vm_flags)) + return do_wp_page(vmf); + if (vmf->flags & FAULT_FLAG_WRITE) { if (!pte_write(entry)) return do_wp_page(vmf);