From patchwork Tue Nov 7 22:15:27 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 10047301 X-Patchwork-Delegate: herbert@gondor.apana.org.au Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 3CA7A6032D for ; Tue, 7 Nov 2017 22:16:24 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 2DC8828904 for ; Tue, 7 Nov 2017 22:16:24 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1FD6528D7A; Tue, 7 Nov 2017 22:16:24 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.5 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, FREEMAIL_FROM, RCVD_IN_DNSWL_HI, RCVD_IN_SORBS_SPAM autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B510128904 for ; Tue, 7 Nov 2017 22:16:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755906AbdKGWQW (ORCPT ); Tue, 7 Nov 2017 17:16:22 -0500 Received: from mail-io0-f195.google.com ([209.85.223.195]:54612 "EHLO mail-io0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755829AbdKGWQV (ORCPT ); Tue, 7 Nov 2017 17:16:21 -0500 Received: by mail-io0-f195.google.com with SMTP id e89so3827736ioi.11; Tue, 07 Nov 2017 14:16:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=pGivlXYZmIba+S0QNvODdkrmftEmPDoy9vvxfA+1cwk=; b=b/VCYQSh3aWdC9S5CK1RWq8BrfnMaNdqkLzAdj3C7RZXgY+v6aGQwWFJYeqJdx/zJs 9sIv0a43z4SiCKxdZ8NyIP25p0dZdrArC2jQOLR5PBQkS++M7MIht0FooDJv4TbCFabB DvFK3O74YQ0DJe1ktqshtivmA+S4cN+3LUYBzSbkL18huitJjamIzuzX3NYTjiDoiy5d t0ZYpje8AShAfRKXYc7fiaQaj/QO51OwMd6ijkSCWNHsgFbH1OfzAjlKZJDRTP2kKEjC DKHv96S+q5L7xTHHJsT5wa7ZVhRJWOhsF1Ern54DUdGtPkoJclFuZyQ4a+AoeygRZRDF iUXQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=pGivlXYZmIba+S0QNvODdkrmftEmPDoy9vvxfA+1cwk=; b=oOSlR6hurg2KoyGoVBrhFS+MQRmc6oMRNiTnP+ryn4Htw++VaQVMWz5ma+6ulCQutv 11zFywRI8F5Jo6bz4NioHsg+hpgQ4hAPUbdprk4E0SxzTlhEad6HAzofJuKEdDbg0xVQ +rmvwoPdi04yLS92PNRUTQORkFkq6UTbtkKx01/GnUumOZ0TJB6YjPwJV5FBkmTpM0VY P5TslreCSg6VyvGj62UJ0jpXelrgmH1K8L2Ex0XPRUHpx8RZuF5Fn57/y34WKHatBayq pbhQ7sQ7UffulMLAVzwFoUl9UON/5ILTtoZlkhQc+8kPMG9nZ1P1Sr+m1p4pgkzG2aRI IAFQ== X-Gm-Message-State: AJaThX4tYEFeNRixTtD40JhdiJYPfB9Cy+r5gMBB6OgWI+WD4SFosULn L2xugnMcOpdWOPTYqJxHzvJR88xW X-Google-Smtp-Source: ABhQp+Q8BDRIwiLB9SbPDwmTyGuDmU2caiHp0hyNrj/RjzY2HgMzGKFdNUsvdc2XFDrH8IVTKPc2ag== X-Received: by 10.107.129.149 with SMTP id l21mr330829ioi.193.1510092980074; Tue, 07 Nov 2017 14:16:20 -0800 (PST) Received: from ebiggers-linuxstation.kir.corp.google.com ([100.66.175.88]) by smtp.gmail.com with ESMTPSA id 80sm1062961ioz.54.2017.11.07.14.16.18 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 07 Nov 2017 14:16:19 -0800 (PST) From: Eric Biggers To: linux-crypto@vger.kernel.org, Herbert Xu Cc: Tudor-Dan Ambarus , Mat Martineau , Salvatore Benedetto , keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, Eric Biggers , stable@vger.kernel.org Subject: [PATCH v2] lib/mpi: call cond_resched() from mpi_powm() loop Date: Tue, 7 Nov 2017 14:15:27 -0800 Message-Id: <20171107221527.98433-1-ebiggers3@gmail.com> X-Mailer: git-send-email 2.15.0.403.gc27cc4dac6-goog Sender: linux-crypto-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Eric Biggers On a non-preemptible kernel, if KEYCTL_DH_COMPUTE is called with the largest permitted inputs (16384 bits), the kernel spends 10+ seconds doing modular exponentiation in mpi_powm() without rescheduling. If all threads do it, it locks up the system. Moreover, it can cause rcu_sched-stall warnings. Notwithstanding the insanity of doing this calculation in kernel mode rather than in userspace, fix it by calling cond_resched() as each bit from the exponent is processed. It's still noninterruptible, but at least it's preemptible now. Do the cond_resched() once per bit rather than once per MPI limb because each limb might still easily take 100+ milliseconds on slow CPUs. Cc: # v4.12+ Signed-off-by: Eric Biggers --- lib/mpi/mpi-pow.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c index e24388a863a7..468fb7cd1221 100644 --- a/lib/mpi/mpi-pow.c +++ b/lib/mpi/mpi-pow.c @@ -26,6 +26,7 @@ * however I decided to publish this code under the plain GPL. */ +#include #include #include "mpi-internal.h" #include "longlong.h" @@ -256,6 +257,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod) } e <<= 1; c--; + cond_resched(); } i--;