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Date: Tue, 28 Feb 2017 16:42:01 +0100 From: Andrea Arcangeli <aarcange@...hat.com> To: Dmitry Vyukov <dvyukov@...gle.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Jan Kara <jack@...e.cz>, ross.zwisler@...ux.intel.com, Michal Hocko <mhocko@...e.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Mike Kravetz <mike.kravetz@...cle.com>, syzkaller <syzkaller@...glegroups.com> Subject: Re: mm: fault in __do_fault Hello Dmitry, On Tue, Feb 28, 2017 at 03:04:53PM +0100, Dmitry Vyukov wrote: > Hello, > > The following program triggers GPF in __do_fault: > https://gist.githubusercontent.com/dvyukov/27345737fca18d92ef761e7fa08aec9b/raw/d99d02511d0bf9a8d6f6bd9c79d373a26924e974/gistfile1.txt Can you verify this fix: >From a65381bc86d2963713b6a9c4a73cded7dd184282 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli <aarcange@...hat.com> Date: Tue, 28 Feb 2017 16:36:59 +0100 Subject: [PATCH 1/1] userfaultfd: shmem: __do_fault requires VM_FAULT_NOPAGE __do_fault assumes vmf->page has been initialized and is valid if VM_FAULT_NOPAGE is not returned by vma->vm_ops->fault(vma, vmf). handle_userfault() in turn should return VM_FAULT_NOPAGE if it doesn't return VM_FAULT_SIGBUS or VM_FAULT_RETRY (the other two possibilities). This VM_FAULT_NOPAGE case is only invoked when signal are pending and it didn't matter for anonymous memory before. It only started to matter since shmem was introduced. hugetlbfs also takes a different path and doesn't exercise __do_fault. Signed-off-by: Andrea Arcangeli <aarcange@...hat.com> --- fs/userfaultfd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index fb6d02b..de28f43 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -500,7 +500,7 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason) * in such case. */ down_read(&mm->mmap_sem); - ret = 0; + ret = VM_FAULT_NOPAGE; } }
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