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 X-Spam-Level: X-Spam-Status: No, score=-6.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5CB55C433E0 for ; Fri, 12 Feb 2021 17:31:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 20C2D64EAC for ; Fri, 12 Feb 2021 17:31:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229797AbhBLRaw (ORCPT ); Fri, 12 Feb 2021 12:30:52 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:35332 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231686AbhBLRar (ORCPT ); Fri, 12 Feb 2021 12:30:47 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613150961; h=from:from: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; bh=7Ue6UWZYwyAvO9YFZKl3E6wcYmOcTl43h7n8qAVY1TQ=; b=aPn2B7Ld+OSgBZgGYgJcNuAbYEAxRbRmIlacIOUhIhu1cxPrHEj8w9WIuVDWiA53GRZ6Da eqbFAWU31ox9LU3AAljaqLMprV3OHHm7ygp3FMhjkkfq5losH4y0qDlE5uioAlNCXEZRBe 3hQxPnz3zKzyfDMRQeialkCSmIOSThs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-108-COOHzF2sOya4tpx2NozfKw-1; Fri, 12 Feb 2021 12:29:18 -0500 X-MC-Unique: COOHzF2sOya4tpx2NozfKw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 47527BBEE2; Fri, 12 Feb 2021 17:29:17 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-113-131.ams2.redhat.com [10.36.113.131]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 23D4E5D9FC; Fri, 12 Feb 2021 17:29:15 +0000 (UTC) From: Florian Weimer To: Andy Lutomirski Cc: linux-mm@kvack.org, linux-api@vger.kernel.org, libc-alpha@sourceware.org Subject: Re: Are vDSO addresses special? References: <87zh0bq62r.fsf@oldenburg.str.redhat.com> <442A16C0-AE5A-4A44-B261-FE6F817EAF3C@amacapital.net> Date: Fri, 12 Feb 2021 18:29:37 +0100 In-Reply-To: <442A16C0-AE5A-4A44-B261-FE6F817EAF3C@amacapital.net> (Andy Lutomirski's message of "Thu, 11 Feb 2021 08:10:42 -0800") Message-ID: <87wnvdgpoe.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org * Andy Lutomirski: >> On Feb 11, 2021, at 2:05 AM, Florian Weimer wrote: >>=20 >> =EF=BB=BFIn glibc, we have some code that copies the DT_SONAME string of= the >> kernel vDSO into the heap, commented this way: >>=20 >> /* Work around a kernel problem. The kernel cannot handle >> addresses in the vsyscall DSO pages in writev() calls. */ >>=20 >> Is this really a problem anymore? vDSO addresses are ordinary userspace >> addresses, I think. (The vsyscall stuff is very different, of course, >> and maybe the vDSO started out the same way.) > > I don=E2=80=99t think it was ever a problem, and it certainly haven=E2=80= =99t been a > problem for a long, long time. vDSO addresses are regular user > addresses. The *vsyscall* addresses are not, and most syscalls will > not accept them, but that shouldn=E2=80=99t matter especially since modern > kernels, by default, won=E2=80=99t let you read those addresses from user= code > either. Thanks. Patch posted: > Saying =E2=80=9Cvsyscall DSO=E2=80=9D is odd. There=E2=80=99s no such thi= ng. In the glibc context, it sometimes means =E2=80=9Csystem-call-like function implemented in the vDSO=E2=80=9D. But that's not the case here. Florian --=20 Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn, Commercial register: Amtsgericht Muenchen, HRB 153243, Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'N= eill