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([2601:646:c200:1ef2:b847:ef6e:681b:6624]) by smtp.gmail.com with ESMTPSA id 17sm6316073pgy.53.2021.02.11.08.10.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Feb 2021 08:10:43 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: Are vDSO addresses special? Date: Thu, 11 Feb 2021 08:10:42 -0800 Message-Id: <442A16C0-AE5A-4A44-B261-FE6F817EAF3C@amacapital.net> References: <87zh0bq62r.fsf@oldenburg.str.redhat.com> Cc: linux-mm@kvack.org, linux-api@vger.kernel.org, libc-alpha@sourceware.org In-Reply-To: <87zh0bq62r.fsf@oldenburg.str.redhat.com> To: Florian Weimer X-Mailer: iPhone Mail (18D52) X-Stat-Signature: nxmadup5ddfkb7qpy4q11uy4enyzk8uz X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: E0F692000D97 Received-SPF: none (amacapital.net>: No applicable sender policy available) receiver=imf01; identity=mailfrom; envelope-from=""; helo=mail-pl1-f175.google.com; client-ip=209.85.214.175 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1613059845-836655 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000321, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > 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 t= he > 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=99= t been a problem for a long, long time. vDSO addresses are regular user addr= esses. The *vsyscall* addresses are not, and most syscalls will not accept t= hem, but that shouldn=E2=80=99t matter especially since modern kernels, by d= efault, won=E2=80=99t let you read those addresses from user code either. Saying =E2=80=9Cvsyscall DSO=E2=80=9D is odd. There=E2=80=99s no such thing.= =E2=80=94Andy=20 >=20 > We only care about Linux 3.2 or later in glibc. >=20 > Thanks, > 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'= Neill >=20