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Sat, 6 Jul 2024 17:15:11 +0800 Message-ID: <3ccb25fa-873d-44d5-d7c4-8385a6152508@huawei.com> Date: Sat, 6 Jul 2024 17:15:10 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH] filemap: replace pte_offset_map() with pte_offset_map_nolock() To: Andrew Morton , , , , , , , , , , , References: <20240313012913.2395414-1-zhangpeng362@huawei.com> <20240625140643.bf4a1a19b0d534d802764610@linux-foundation.org> <20240704114039.4fd0739593cd0a96fe428496@linux-foundation.org> Content-Language: en-US From: "zhangpeng (AS)" In-Reply-To: <20240704114039.4fd0739593cd0a96fe428496@linux-foundation.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.160] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemm600020.china.huawei.com (7.193.23.147) X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 8E15F80025 X-Stat-Signature: yxb1jfx6i8gofi8iokukyjuf6ofnzjk3 X-HE-Tag: 1720257317-491577 X-HE-Meta: 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 j+15fHJJ 6CKmOF2ZT+pHv2q7lfYHXQtaTBqHL8fJNgmQOlSrxpBqlA3QWq8l94xhNWmf/pXiaetO7SwB5d4H+6kYjptcekRJSXsc0uN6SKObt4exhwttEWQHRd7KznXUAqIoQKbYLMGlE4URAJbxqnmmtvAtadYEUD/pXPNY5Q3gM1Ksrho5Kxsz02S15ClzZnAr+pafzK5W1oPkuG80ko/fcX3uyaHKzC+0ePpIWkvGm1vrMxxOKXtATLHaY/HSMISKF0zwOpNdQVGVV51Gptxk= 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 2024/7/5 2:40, Andrew Morton wrote: > On Tue, 25 Jun 2024 14:06:43 -0700 Andrew Morton wrote: > >> 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? >> > Nobody? > > Oh well, I'll add cc:stable amd move this into mm-hotfixes. > Sorry for the late reply. As David said, the PTL pointer might be stale so if we continue to use it infilemap_fault_recheck_pte_none(), it might trigger UAF. Also, if the PTL fails, the issue fixed by commit 58f327f2ce80 ("filemap: avoid unnecessary major faults in filemap_fault()") might reappear. -- Best Regards, Peng