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h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=lVVNBFfmth+dtWyl6uliVwssxGOrcmuCM84uUz46PtSf6FN5gIQaRiEOsmIxVpsLm LW/Te0JY3B+HcZ2MdHVxQdg7ste/Q7XofWLTaDhXM9y+F8Dn26w92bpuX18mZQUD0I z0+u2x5fdY4lJF7rktGCuB/HDd0kdPzGV2NNY1u4= Date: Tue, 25 Jun 2024 14:06:43 -0700 From: Andrew Morton To: Peng Zhang Cc: , , , , , , , , , , Subject: Re: [PATCH] filemap: replace pte_offset_map() with pte_offset_map_nolock() Message-Id: <20240625140643.bf4a1a19b0d534d802764610@linux-foundation.org> In-Reply-To: <20240313012913.2395414-1-zhangpeng362@huawei.com> References: <20240313012913.2395414-1-zhangpeng362@huawei.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: a46sixkacf6j7m8c3m3qkcs7ioh47nki X-Rspamd-Queue-Id: 2EFDEA0006 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1719349607-494797 X-HE-Meta: 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 NfQISPMx 5+J575ntduuqzC5A9v72rZp40WCnOYbVm6Ka30dWxeH5Zs3aBjxIl8HaUq6I3Opn9hGspP3z+R5JgKNUsokYNpCQ2Ma4jccKCbOUnJsBTG4LpGbUQo3VKJsRm2iQJHs772Hb99fqWB3WeTYRrcS7PHB7XgFBC3jllATPJGCYpEzVeSV3pbrstasiCw665iak6IqwCxTyHb5QZ5nJ3oYd/ZsKXKMdEgR+lVVnnNy8zaoCt7A0OEETWp9cYsJDTcoS6qgl6ukQ2suAa+puZcrDoaRpslUoG1I11CF3Uj3WEVl2utRg= 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: List-Subscribe: List-Unsubscribe: On Wed, 13 Mar 2024 09:29:13 +0800 Peng Zhang wrote: > From: ZhangPeng > > The vmf->ptl in filemap_fault_recheck_pte_none() is still set from > handle_pte_fault(). But at the same time, we did a pte_unmap(vmf->pte). > After a pte_unmap(vmf->pte) unmap and rcu_read_unlock(), the page table > may be racily changed and vmf->ptl maybe fails to protect the actual > page table. > Fix this by replacing pte_offset_map() with pte_offset_map_nolock(). > > ... > > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3207,7 +3207,8 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf) > if (!(vmf->flags & FAULT_FLAG_ORIG_PTE_VALID)) > return 0; > > - ptep = pte_offset_map(vmf->pmd, vmf->address); > + ptep = pte_offset_map_nolock(vma->vm_mm, vmf->pmd, vmf->address, > + &vmf->ptl); > if (unlikely(!ptep)) > return VM_FAULT_NOPAGE; > whoops, I'm still sitting on this because I didn't know whether we should backport it. And... guess what I say next. Can we please describe what are the userspace visible effects of the bug?