From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from theia.8bytes.org (8bytes.org [81.169.241.247]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5CC0A72 for ; Wed, 19 May 2021 13:16:41 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id 63C252FA; Wed, 19 May 2021 15:16:39 +0200 (CEST) Date: Wed, 19 May 2021 15:16:38 +0200 From: Joerg Roedel To: Sean Christopherson Cc: x86@kernel.org, Hyunwook Baek , Joerg Roedel , stable@vger.kernel.org, hpa@zytor.com, Andy Lutomirski , Dave Hansen , Peter Zijlstra , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Martin Radev , Arvind Sankar , linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH 2/6] x86/sev-es: Forward page-faults which happen during emulation Message-ID: References: <20210512075445.18935-1-joro@8bytes.org> <20210512075445.18935-3-joro@8bytes.org> X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Sean, On Wed, May 12, 2021 at 05:31:03PM +0000, Sean Christopherson wrote: > This got me looking at the flows that "inject" #PF, and I'm pretty sure there > are bugs in __vc_decode_user_insn() + insn_get_effective_ip(). > > Problem #1: __vc_decode_user_insn() assumes a #PF if insn_fetch_from_user_inatomic() > fails, but the majority of failure cases in insn_get_seg_base() are #GPs, not #PF. > > res = insn_fetch_from_user_inatomic(ctxt->regs, buffer); > if (!res) { > ctxt->fi.vector = X86_TRAP_PF; > ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER; > ctxt->fi.cr2 = ctxt->regs->ip; > return ES_EXCEPTION; > } > > Problem #2: Using '0' as an error code means a legitimate effective IP of '0' > will be misinterpreted as a failure. Practically speaking, I highly doubt anyone > will ever actually run code at address 0, but it's technically possible. The > most robust approach would be to pass a pointer to @ip and return an actual error > code. Using a non-canonical magic value might also work, but that could run afoul > of future shenanigans like LAM. > > ip = insn_get_effective_ip(regs); > if (!ip) > return 0; Your observations are all correct. I put some changes onto this patch-set to fix these problems. Regards, Joerg 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=-3.7 required=3.0 tests=BAYES_00, 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 73107C433ED for ; Wed, 19 May 2021 13:16:49 +0000 (UTC) Received: from smtp3.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id EB6DE613AA for ; Wed, 19 May 2021 13:16:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB6DE613AA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=virtualization-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp3.osuosl.org (Postfix) with ESMTP id B18D06067E; Wed, 19 May 2021 13:16:48 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp3.osuosl.org ([127.0.0.1]) by localhost (smtp3.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id hKHZDREjn9XP; Wed, 19 May 2021 13:16:46 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp3.osuosl.org (Postfix) with ESMTP id 328D7605EC; Wed, 19 May 2021 13:16:45 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 02272C000E; Wed, 19 May 2021 13:16:45 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id CDF7CC0001 for ; Wed, 19 May 2021 13:16:43 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id AE8594020C for ; Wed, 19 May 2021 13:16:43 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id xvIRNSg6dF7d for ; Wed, 19 May 2021 13:16:43 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.8.0 Received: from theia.8bytes.org (8bytes.org [IPv6:2a01:238:4383:600:38bc:a715:4b6d:a889]) by smtp2.osuosl.org (Postfix) with ESMTPS id 1A89C4011B for ; Wed, 19 May 2021 13:16:42 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id 63C252FA; Wed, 19 May 2021 15:16:39 +0200 (CEST) Date: Wed, 19 May 2021 15:16:38 +0200 From: Joerg Roedel To: Sean Christopherson Subject: Re: [PATCH 2/6] x86/sev-es: Forward page-faults which happen during emulation Message-ID: References: <20210512075445.18935-1-joro@8bytes.org> <20210512075445.18935-3-joro@8bytes.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Cc: kvm@vger.kernel.org, Peter Zijlstra , Dave Hansen , virtualization@lists.linux-foundation.org, Arvind Sankar , hpa@zytor.com, Jiri Slaby , x86@kernel.org, David Rientjes , Martin Radev , Tom Lendacky , Joerg Roedel , Kees Cook , Cfir Cohen , Hyunwook Baek , linux-coco@lists.linux.dev, Andy Lutomirski , Dan Williams , Juergen Gross , Mike Stunes , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Masami Hiramatsu , Erdem Aktas X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" Hi Sean, On Wed, May 12, 2021 at 05:31:03PM +0000, Sean Christopherson wrote: > This got me looking at the flows that "inject" #PF, and I'm pretty sure there > are bugs in __vc_decode_user_insn() + insn_get_effective_ip(). > > Problem #1: __vc_decode_user_insn() assumes a #PF if insn_fetch_from_user_inatomic() > fails, but the majority of failure cases in insn_get_seg_base() are #GPs, not #PF. > > res = insn_fetch_from_user_inatomic(ctxt->regs, buffer); > if (!res) { > ctxt->fi.vector = X86_TRAP_PF; > ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER; > ctxt->fi.cr2 = ctxt->regs->ip; > return ES_EXCEPTION; > } > > Problem #2: Using '0' as an error code means a legitimate effective IP of '0' > will be misinterpreted as a failure. Practically speaking, I highly doubt anyone > will ever actually run code at address 0, but it's technically possible. The > most robust approach would be to pass a pointer to @ip and return an actual error > code. Using a non-canonical magic value might also work, but that could run afoul > of future shenanigans like LAM. > > ip = insn_get_effective_ip(regs); > if (!ip) > return 0; Your observations are all correct. I put some changes onto this patch-set to fix these problems. Regards, Joerg _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization