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Sat, 29 Nov 2025 12:06:37 +0800 (CST) Received: from kwepemj100009.china.huawei.com (unknown [7.202.194.3]) by mail.maildlp.com (Postfix) with ESMTPS id 950921A0191; Sat, 29 Nov 2025 12:08:26 +0800 (CST) Received: from DESKTOP-A37P9LK.huawei.com (10.67.109.17) by kwepemj100009.china.huawei.com (7.202.194.3) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Sat, 29 Nov 2025 12:08:25 +0800 From: Xie Yuanbin To: , , , , , CC: , , , , , , , , , , , , , , , Subject: Re: [Bug report] hash_name() may cross page boundary and trigger Date: Sat, 29 Nov 2025 12:08:17 +0800 Message-ID: <20251129040817.65356-1-xieyuanbin1@huawei.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.67.109.17] X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To kwepemj100009.china.huawei.com (7.202.194.3) X-Stat-Signature: krqtefpanam54rrg77aqskdnca7zfbsj X-Rspam-User: X-Rspamd-Queue-Id: 6B853100012 X-Rspamd-Server: rspam09 X-HE-Tag: 1764389311-865841 X-HE-Meta: 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 7ITQwCU4 rCVFlq+4DBfGSa0GY1nRNrp0WeZbYwFQrVtasUcokqKH7jBy8KGIqtbGh3/jEOT7ez7P6g9Ghli7/fK7AdJQhKydUqgKaFbgj5odD0ti3Np1nYlZ8vbqJfMqGu8roM6J8rxCNvpfk7IYPGvwviDJ6v1xTAW1qXw3/pXNQU9AxDDxAFB7azbPbO2nE6nZXCKm4gcKziPZTp/yHukvHrqWdZVNSu4FJ2nE+JE97OjBfwyQMUGilQ0HCfj87p80rZ4LK9PyyC6eE09XtAaE0qo+dp5DVcRTYs/wVSV5yAwI425xe7HllJASxGjDlDBWnL6blppWjlWRNZ6sLchAzBCz32j6f9mvwuSEuetE11K9iTJxPRljRFzbSbVh6r0It7VlQ3RLSCCMgrQgdNMJBmsRJP+9s+HRv+up3b7fo 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 Fri, 28 Nov 2025 17:35:37 -0800, Linus Torvalds wrote: > On Fri, 28 Nov 2025 at 17:01, Zizhi Wo wrote: >> It has an additional check to determine reg: >> >> if (unlikely(addr > TASK_SIZE) && !user_mode(regs)) >> goto no_context; >> >> I'd like to ask if this "regs" examination also needs to be brought >> along? > > That seems unnecessary. > > Yes, in this case the original problem you reported with sleeping in > an RCU region was triggered by a kernel access, and a user-space > access would never have caused any such issues. > > So checking for !user_mode(regs) isn't exactly *wrong*. > > But while it isn't wrong, I think it's also kind of pointless. > > Because regardless of whether it's a kernel or user space access, an > access outside TASK_SIZE shouldn't be associated with a valid user > space context, so the code might as well just go to the "no_context" > label directly. > > That said, somebody should definitely double-check me - because I > think arm also did the vdso trick at high addresses that i386 used to > do, so there is the fake VDSO thing up there. > > But if you get a page fault on that, it's not going to be fixed up, so > even if user space can access it, there's no point in looking that > fake vm area up for page faults. I think the `user_mode(regs)` check is necessary because the label no_context actually jumps to __do_kernel_fault(), whereas page fault from user mode should jump to `__do_user_fault()`. Alternatively, we would need to change `goto no_context` to `goto bad_area`. Or perhaps I misunderstood something, please point it out. Thanks very much! Xie Yuanbin