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=-0.7 required=3.0 tests=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 956FBC38A2A for ; Thu, 7 May 2020 18:22:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 71033215A4 for ; Thu, 7 May 2020 18:22:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728237AbgEGSWd (ORCPT ); Thu, 7 May 2020 14:22:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1728198AbgEGSWb (ORCPT ); Thu, 7 May 2020 14:22:31 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D1F5C05BD43; Thu, 7 May 2020 11:22:31 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jWl9z-0002qB-Ia; Thu, 07 May 2020 20:22:15 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id B9DAE102652; Thu, 7 May 2020 20:22:14 +0200 (CEST) From: Thomas Gleixner To: Yu-cheng Yu , linux-kernel@vger.kernel.org, x86@kernel.org, "H. Peter Anvin" , Ingo Molnar , Dave Hansen , Tony Luck , Andy Lutomirski , Borislav Petkov , Rik van Riel , "Ravi V. Shankar" , Sebastian Andrzej Siewior , Fenghua Yu , Peter Zijlstra Cc: Yu-cheng Yu , sam , Kees Cook , Alexey Dobriyan , Dave Hansen , Jann Horn , Andrew Morton , Alexander Potapenko , Al Viro , stable@vger.kernel.org Subject: Re: [PATCH] x86/fpu/xstate: Clear uninitialized xstate areas in core dump In-Reply-To: <20200507164904.26927-1-yu-cheng.yu@intel.com> References: <20200507164904.26927-1-yu-cheng.yu@intel.com> Date: Thu, 07 May 2020 20:22:14 +0200 Message-ID: <87lfm3ehbd.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Yu-cheng Yu writes: > @@ -983,6 +983,7 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of > { > unsigned int offset, size; > struct xstate_header header; > + int last_off; > int i; > > /* > @@ -1006,7 +1007,17 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of > > __copy_xstate_to_kernel(kbuf, &header, offset, size, size_total); > > + last_off = 0; > + > for (i = 0; i < XFEATURE_MAX; i++) { > + /* > + * Clear uninitialized area before XSAVE header. > + */ > + if (i == FIRST_EXTENDED_XFEATURE) { > + memset(kbuf + last_off, 0, XSAVE_HDR_OFFSET - last_off); > + last_off = XSAVE_HDR_OFFSET + XSAVE_HDR_SIZE; > + } > + > /* > * Copy only in-use xstates: > */ > @@ -1020,11 +1031,16 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of > if (offset + size > size_total) > break; > > + memset(kbuf + last_off, 0, offset - last_off); > + last_off = offset + size; > + > __copy_xstate_to_kernel(kbuf, src, offset, size, size_total); > } > > } > > + memset(kbuf + last_off, 0, size_total - last_off); Why doing all this partial zeroing? There is absolutely no point. Either the caller clears the buffer or this function clears it right at the beginning with: memset(kbuf, 0, min(size_total, XSAVE_MAX_SIZE)); Thanks, tglx