From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7B0ADC433EF for ; Thu, 7 Jul 2022 08:57:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F1D9A6B0072; Thu, 7 Jul 2022 04:57:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id ECE706B0073; Thu, 7 Jul 2022 04:57:31 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D96176B0074; Thu, 7 Jul 2022 04:57:31 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id CA0AC6B0072 for ; Thu, 7 Jul 2022 04:57:31 -0400 (EDT) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay11.hostedemail.com (Postfix) with ESMTP id A0FFD80669 for ; Thu, 7 Jul 2022 08:57:31 +0000 (UTC) X-FDA: 79659700302.27.F9B7546 Received: from mail-yw1-f171.google.com (mail-yw1-f171.google.com [209.85.128.171]) by imf01.hostedemail.com (Postfix) with ESMTP id 4C83B40013 for ; Thu, 7 Jul 2022 08:57:31 +0000 (UTC) Received: by mail-yw1-f171.google.com with SMTP id 00721157ae682-31c8bb90d09so109815657b3.8 for ; Thu, 07 Jul 2022 01:57:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=hxxPRIfRZ6kDlNJS/WoodDXQuHq7aEJrE7gGVlQfxtc=; b=ZmyUgdvMu6NZCSWtYE6O6bzfid1hYCJsA7WyF7VN2wseRhfi03QNLKlYGcZZtXLGEJ RTF2FqOAwVxGBekRl3B9p48InGj1uoc/j7Q6nJ6sfHlOq89OKAMiRcDIy8QqsyEvrnRn LtmJypAw8lzH7McW1PPBK663RQuWJ5IMBs5xGFttjpi/nPfgjq+BEg0SDZiRL/uY6cyT 9RgpawoxCGaMe57GPQgJRyNSeEpyA2Rml9efUjdp1DmHrt6WvJz+qMY9Xz/m2mm56DZv Qn5QCfb1BrT2/2pEI9nCqlOmZa/CIFjCNHza/sTkGLBbQw3Nbgxng4QfCrgrnu3ZrA8a M24Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=hxxPRIfRZ6kDlNJS/WoodDXQuHq7aEJrE7gGVlQfxtc=; b=5iGnxIVvHXytcGLEHvLnAs5lDKvGbnT2i/+KLhS1aggOnvZEccga0byLQfz8pQ9eRy 3CY7gUzzM1DZ7KFEGVtGj31xpCFgEvuuKGz7y1hsjKBoNwu4IqotcWrWjNqgsRX+PZp8 Z366EyX+N2ZL+s/F29yt7UQV1T9RIYBJGbxXFdAnnXuqVPAZzb+UOej22zxISHOCpVCp tNrVQ3Qn0HfIHFlIA6K4jYbZVg/yETzeqx2vvM3VXbnALIKP8Z/y4cEQfZfPn6VbKGtz 3zYbMCHCL7BgkBBDK7u7gSAZrP0clnKD2dOCV+bzOCfb54bSS9+xRIoAGPCRTceIlujO 8g2Q== X-Gm-Message-State: AJIora/deJym4XJzIMOIfIdvf6MWYDsXlFR0Jn/Zfz+yBsI+sTS8U/BO jvJmvjNalZJEila7SbrV+V+uIgeLLr0I6DPW06+rxA== X-Google-Smtp-Source: AGRyM1u5n+5YHZaW5ne094F1MJ3Dh/iwnzn5Yo8ytzAmgsdWnzH5qYppBnkr6xJWsGT8xbgLo+p+vGyX8BjAF/7xOes= X-Received: by 2002:a0d:e905:0:b0:31c:9616:1fc5 with SMTP id s5-20020a0de905000000b0031c96161fc5mr24879363ywe.265.1657184248976; Thu, 07 Jul 2022 01:57:28 -0700 (PDT) MIME-Version: 1.0 References: <20220622162230.83474-1-kirill.shutemov@linux.intel.com> <20220622162230.83474-4-kirill.shutemov@linux.intel.com> <20220706231349.4ghhewbfpzjln56u@black.fi.intel.com> In-Reply-To: <20220706231349.4ghhewbfpzjln56u@black.fi.intel.com> From: Alexander Potapenko Date: Thu, 7 Jul 2022 10:56:53 +0200 Message-ID: Subject: Re: [PATCHv4 3/8] mm: Pass down mm_struct to untagged_addr() To: "Kirill A. Shutemov" Cc: Dave Hansen , Andy Lutomirski , Peter Zijlstra , "the arch/x86 maintainers" , Kostya Serebryany , Andrey Ryabinin , Andrey Konovalov , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657184251; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=hxxPRIfRZ6kDlNJS/WoodDXQuHq7aEJrE7gGVlQfxtc=; b=CG27M589L4OBnjLDGsj9zn+y+PyXOS1MJTOiVPaqYIn+xdpKf0rTJD2XBqW0N9+u6AKH8G u3m5Cww0x8ZhOFDTAVBG27+shh8cPYiJROsbOnoWPRuj/PDojGfXxChNs3fjKYsSpH9YWZ hgFTZECLTF+64/vpyLuSDQdWzP8qCqE= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=ZmyUgdvM; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf01.hostedemail.com: domain of glider@google.com designates 209.85.128.171 as permitted sender) smtp.mailfrom=glider@google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657184251; a=rsa-sha256; cv=none; b=1BXCU13StF2bh+ydOmMXLPZffcfjLBRoGwD5S+4uyJqcy86jGFFA7aawtdYcJV7/bWh5AP 7m7uq20nAQUa0RRtenCtbgkBxiTmxkjrWZdT6wsY5rL66YDhn0QBC2Sko9n9vzMpnXM1hA ZM9NvhGEj3/2AG2pOkajWKbdSMsOEnk= X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: xf66a69chq8b6m14ofef11d4nsphpwzf X-Rspamd-Queue-Id: 4C83B40013 Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=ZmyUgdvM; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf01.hostedemail.com: domain of glider@google.com designates 209.85.128.171 as permitted sender) smtp.mailfrom=glider@google.com X-HE-Tag: 1657184251-919105 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: On Thu, Jul 7, 2022 at 1:14 AM Kirill A. Shutemov wrote: > > On Tue, Jul 05, 2022 at 05:42:21PM +0200, Alexander Potapenko wrote: > > Kirill, > > > > > > > diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c > > > index feeb935a2299..abc096a68f05 100644 > > > --- a/lib/strnlen_user.c > > > +++ b/lib/strnlen_user.c > > > @@ -97,7 +97,7 @@ long strnlen_user(const char __user *str, long coun= t) > > > return 0; > > > > > > max_addr =3D TASK_SIZE_MAX; > > > - src_addr =3D (unsigned long)untagged_addr(str); > > > + src_addr =3D (unsigned long)untagged_addr(current->mm, str); > > > > In a downstream kernel with LAM disabled I'm seeing current->mm being > > NULL at this point, because strnlen_user() is being called by > > kdevtmpfs. > > IIUC current->mm is only guaranteed to be non-NULL in the userspace > > process context, whereas untagged_addr() may get called in random > > places. > > > > Am I missing something? > > Hm. Could you show a traceback? > > As strnlen_user() intended to be used on an user string I expected it to > be called from a process context. I guess I'm wrong, but I don't yet > understand why. Oh, I see now. The old implementation of devtmpfsd() (https://elixir.bootlin.com/linux/v5.4/source/drivers/base/devtmpfs.c#L397) uses ksys_mount(), which assumes that the strings must be copied from the userspace, whereas they are actually constants in kernel .rodata Wonder if the validity of mm->current for userspace accesses is actually enforced anyhow in newer kernels. > -- > Kirill A. Shutemov --=20 Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Stra=C3=9Fe, 33 80636 M=C3=BCnchen Gesch=C3=A4ftsf=C3=BChrer: Paul Manicle, Liana Sebastian Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg