From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:58018 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731565AbeK3Bas (ORCPT ); Thu, 29 Nov 2018 20:30:48 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Aneesh Kumar K.V" , "Kirill A. Shutemov" , Willem de Bruijn , Eric Dumazet , Ido Schimmel , Andrew Morton , Linus Torvalds Subject: [PATCH 4.14 029/100] mm/memory.c: recheck page table entry with page table lock held Date: Thu, 29 Nov 2018 15:11:59 +0100 Message-Id: <20181129140101.264750396@linuxfoundation.org> In-Reply-To: <20181129140058.768942700@linuxfoundation.org> References: <20181129140058.768942700@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aneesh Kumar K.V commit ff09d7ec9786be4ad7589aa987d7dc66e2dd9160 upstream. We clear the pte temporarily during read/modify/write update of the pte. If we take a page fault while the pte is cleared, the application can get SIGBUS. One such case is with remap_pfn_range without a backing vm_ops->fault callback. do_fault will return SIGBUS in that case. cpu 0 cpu1 mprotect() ptep_modify_prot_start()/pte cleared. . . page fault. . . prep_modify_prot_commit() Fix this by taking page table lock and rechecking for pte_none. [aneesh.kumar@linux.ibm.com: fix crash observed with syzkaller run] Link: http://lkml.kernel.org/r/87va6bwlfg.fsf@linux.ibm.com Link: http://lkml.kernel.org/r/20180926031858.9692-1-aneesh.kumar@linux.ibm.com Signed-off-by: Aneesh Kumar K.V Acked-by: Kirill A. Shutemov Cc: Willem de Bruijn Cc: Eric Dumazet Cc: Ido Schimmel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/memory.c | 34 ++++++++++++++++++++++++++++++---- 1 file changed, 30 insertions(+), 4 deletions(-) --- a/mm/memory.c +++ b/mm/memory.c @@ -3697,10 +3697,36 @@ static int do_fault(struct vm_fault *vmf struct vm_area_struct *vma = vmf->vma; int ret; - /* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND */ - if (!vma->vm_ops->fault) - ret = VM_FAULT_SIGBUS; - else if (!(vmf->flags & FAULT_FLAG_WRITE)) + /* + * The VMA was not fully populated on mmap() or missing VM_DONTEXPAND + */ + if (!vma->vm_ops->fault) { + /* + * If we find a migration pmd entry or a none pmd entry, which + * should never happen, return SIGBUS + */ + if (unlikely(!pmd_present(*vmf->pmd))) + ret = VM_FAULT_SIGBUS; + else { + vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, + vmf->pmd, + vmf->address, + &vmf->ptl); + /* + * Make sure this is not a temporary clearing of pte + * by holding ptl and checking again. A R/M/W update + * of pte involves: take ptl, clearing the pte so that + * we don't have concurrent modification by hardware + * followed by an update. + */ + if (unlikely(pte_none(*vmf->pte))) + ret = VM_FAULT_SIGBUS; + else + ret = VM_FAULT_NOPAGE; + + pte_unmap_unlock(vmf->pte, vmf->ptl); + } + } else if (!(vmf->flags & FAULT_FLAG_WRITE)) ret = do_read_fault(vmf); else if (!(vma->vm_flags & VM_SHARED)) ret = do_cow_fault(vmf);