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Fri, 19 Mar 2021 08:25:10 -0700 (PDT) Received: from localhost.localdomain ([113.172.181.219]) by smtp.gmail.com with ESMTPSA id d138sm336346pfd.55.2021.03.19.08.25.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Mar 2021 08:25:10 -0700 (PDT) From: Bui Quang Minh To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, minhquangbui99@gmail.com Subject: [PATCH] userfaultfd: Write protect when virtual memory range has no page table entry Date: Fri, 19 Mar 2021 22:24:28 +0700 Message-Id: <20210319152428.52683-1-minhquangbui99@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Stat-Signature: fbpqorq1jtc4yf6ggp6ggqgtinr63h1s X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: AC926408E5EF Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf10; identity=mailfrom; envelope-from=""; helo=mail-pj1-f44.google.com; client-ip=209.85.216.44 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616167512-253353 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000007, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: userfaultfd_writeprotect() use change_protection() to clear write bit in page table entries (pte/pmd). So, later write to this virtual address range causes a page fault, which is then handled by userspace program. However, change_protection() has no effect when there is no page table entries associated with that virtual memory range (a newly mapped memory range). As a result, later access to that memory range causes allocating a page table entry with write bit still set (due to VM_WRITE flag in vma->vm_flags). Add checks for VM_UFFD_WP in vma->vm_flags when allocating new page table entry in missing page table entry page fault path. Signed-off-by: Bui Quang Minh --- mm/huge_memory.c | 12 ++++++++++++ mm/memory.c | 10 ++++++++++ 2 files changed, 22 insertions(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index ae907a9c2050..9bb16a55a48c 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -636,6 +636,11 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf, entry = mk_huge_pmd(page, vma->vm_page_prot); entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); + if (userfaultfd_wp(vma)) { + entry = pmd_wrprotect(entry); + entry = pmd_mkuffd_wp(entry); + } + page_add_new_anon_rmap(page, vma, haddr, true); lru_cache_add_inactive_or_unevictable(page, vma); pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable); @@ -643,6 +648,13 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf, update_mmu_cache_pmd(vma, vmf->address, vmf->pmd); add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR); mm_inc_nr_ptes(vma->vm_mm); + + if (userfaultfd_huge_pmd_wp(vma, *vmf->pmd)) { + spin_unlock(vmf->ptl); + count_vm_event(THP_FAULT_ALLOC); + count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC); + return handle_userfault(vmf, VM_UFFD_WP); + } spin_unlock(vmf->ptl); count_vm_event(THP_FAULT_ALLOC); count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC); diff --git a/mm/memory.c b/mm/memory.c index 5efa07fb6cdc..b835746545bf 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3564,6 +3564,11 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) if (vma->vm_flags & VM_WRITE) entry = pte_mkwrite(pte_mkdirty(entry)); + if (userfaultfd_wp(vma)) { + entry = pte_wrprotect(entry); + entry = pte_mkuffd_wp(entry); + } + vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); if (!pte_none(*vmf->pte)) { @@ -3590,6 +3595,11 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) /* No need to invalidate - it was non-present before */ update_mmu_cache(vma, vmf->address, vmf->pte); + + if (userfaultfd_pte_wp(vma, *vmf->pte)) { + pte_unmap_unlock(vmf->pte, vmf->ptl); + return handle_userfault(vmf, VM_UFFD_WP); + } unlock: pte_unmap_unlock(vmf->pte, vmf->ptl); return ret;