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Fri, 24 Jan 2020 07:25:52 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id YWp1fOtM3W3N; Fri, 24 Jan 2020 07:25:52 +0100 (CET) Received: from [172.25.230.111] (po15451.idsi0.si.c-s.fr [172.25.230.111]) by messagerie.si.c-s.fr (Postfix) with ESMTP id F08338B768; Fri, 24 Jan 2020 07:25:51 +0100 (CET) Subject: Re: [PATCH] lib: Reduce user_access_begin() boundaries in strncpy_from_user() and strnlen_user() To: Linus Torvalds , linux-arch Cc: Andrew Morton , Linux Kernel Mailing List , linuxppc-dev , Linux-MM References: <70f99f7474826883877e84f93224e937d9c974de.1579767339.git.christophe.leroy@c-s.fr> From: Christophe Leroy Message-ID: <8de7ba48-7bf4-8d43-5dfc-dacf34f80537@c-s.fr> Date: Fri, 24 Jan 2020 07:25:51 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: quoted-printable 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: Le 23/01/2020 =C3=A0 19:47, Linus Torvalds a =C3=A9crit=C2=A0: > On Thu, Jan 23, 2020 at 12:34 AM Christophe Leroy > wrote: >> >> The range passed to user_access_begin() by strncpy_from_user() and >> strnlen_user() starts at 'src' and goes up to the limit of userspace >> allthough reads will be limited by the 'count' param. >> >> On 32 bits powerpc (book3s/32) access has to be granted for each 256Mb= ytes >> segment and the cost increases with the number of segments to unlock. >> >> Limit the range with 'count' param. >=20 > Ack. I'm tempted to take this for 5.5 too, just so that the > unquestionably trivial fixes are in that baseline, and the > infrastructure is ready for any architecture that has issues like > this. It would be nice, then the user_access_begin stuff for powerpc could go=20 for 5.6 without worring about. Thanks Christophe