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=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 91A1DC4346E for ; Tue, 29 Sep 2020 05:33:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 58DF720BED for ; Tue, 29 Sep 2020 05:33:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727035AbgI2Fdp (ORCPT ); Tue, 29 Sep 2020 01:33:45 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:33832 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725819AbgI2Fdo (ORCPT ); Tue, 29 Sep 2020 01:33:44 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4C0p2r3TPVz9txQw; Tue, 29 Sep 2020 07:33:40 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id TIqEvTt6Jfz6; Tue, 29 Sep 2020 07:33:40 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4C0p2r28n5z9txQv; Tue, 29 Sep 2020 07:33:40 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 4DC678B79F; Tue, 29 Sep 2020 07:33:41 +0200 (CEST) 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 3fyGxHwIxsx4; Tue, 29 Sep 2020 07:33:41 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 982908B76C; Tue, 29 Sep 2020 07:33:40 +0200 (CEST) Subject: Re: [PATCH v2 23/25] powerpc/signal: Create 'unsafe' versions of copy_[ck][fpr/vsx]_to_user() From: Christophe Leroy To: "Christopher M. Riedl" , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org References: Message-ID: <61bd2283-94bb-edff-5140-8be2b98a02e3@csgroup.eu> Date: Tue, 29 Sep 2020 07:33:30 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 29/09/2020 à 07:22, Christophe Leroy a écrit : > > > Le 29/09/2020 à 04:04, Christopher M. Riedl a écrit : >> On Tue Aug 18, 2020 at 12:19 PM CDT, Christophe Leroy wrote: >>> For the non VSX version, that's trivial. Just use unsafe_copy_to_user() >>> instead of __copy_to_user(). >>> >>> For the VSX version, remove the intermediate step through a buffer and >>> use unsafe_put_user() directly. This generates a far smaller code which >>> is acceptable to inline, see below: >>> >>> >>> Signed-off-by: Christophe Leroy >>> --- >>> arch/powerpc/kernel/signal.h | 53 ++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 53 insertions(+) >>> >>> diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h >>> index f610cfafa478..2559a681536e 100644 >>> --- a/arch/powerpc/kernel/signal.h >>> +++ b/arch/powerpc/kernel/signal.h >>> @@ -32,7 +32,54 @@ unsigned long copy_fpr_to_user(void __user *to, >>> struct task_struct *task); >>> unsigned long copy_ckfpr_to_user(void __user *to, struct task_struct >>> *task); >>> unsigned long copy_fpr_from_user(struct task_struct *task, void __user >>> *from); >>> unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user >>> *from); >>> + >>> +#define unsafe_copy_fpr_to_user(to, task, label) do { \ >>> + struct task_struct *__t = task; \ >>> + u64 __user *buf = (u64 __user *)to; \ >>> + int i; \ >>> + \ >>> + for (i = 0; i < ELF_NFPREG - 1 ; i++) \ >>> + unsafe_put_user(__t->thread.TS_FPR(i), &buf[i], label); \ >>> + unsafe_put_user(__t->thread.fp_state.fpscr, &buf[i], label); \ >>> +} while (0) >>> + >> >> I've been working on the PPC64 side of this "unsafe" rework using this >> series as a basis. One question here - I don't really understand what >> the benefit of re-implementing this logic in macros (similarly for the >> other copy_* functions below) is? > > Not sure either. > > The whole purpose is to not manage the error through a local var but exclusively use labels. > However, GCC is probably smart enough to understand it and drop the local var while inlining. > > One important thing however is to make sure we won't end up with an outline function, otherwise you > completely loose the benefit of the label stuff. And you get a function call inside a user access, > which is what we want to avoid. > >> >> I am considering  a "__unsafe_copy_*" implementation in signal.c for >> each (just the original implementation w/ using the "unsafe_" variants >> of the uaccess stuff) which gets called by the "safe" functions w/ the >> appropriate "user_*_access_begin/user_*_access_end". Something like >> (pseudo-ish code): > > Good idea, however ... > >> >>     /* signal.c */ >>     unsigned long __unsafe_copy_fpr_to_user(...) >>     { >>         ... >>         unsafe_copy_to_user(..., bad); >>         return 0; >>     bad: >>         return 1; /* -EFAULT? */ >>     } > > This __unsafe_copy_fpr_to_user() has to be in signal.h and must be tagged 'static __always_inline' > for the reasons explained above. > >> >>     unsigned long copy_fpr_to_user(...) >>     { >>         unsigned long err; >>         if (!user_write_access_begin(...)) >>             return 1; /* -EFAULT? */ >> >>         err = __unsafe_copy_fpr_to_user(...); >> >>         user_write_access_end(); >>         return err; >>     } Also note that at the end (ie when both PPC32 and PPC64 signal code are using "unsafe" versions), the "safe" version won't be used anymore and will be dropped. Christophe