From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Martin Subject: [PATCH 08/14] KVM: arm64/sve: WARN when avoiding divide-by-zero in sve_reg_to_region() Date: Fri, 12 Apr 2019 17:28:12 +0100 Message-ID: <1555086498-26691-9-git-send-email-Dave.Martin@arm.com> References: <1555086498-26691-1-git-send-email-Dave.Martin@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 91BFD4A4C5 for ; Fri, 12 Apr 2019 12:29:25 -0400 (EDT) Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ED5OWQNKPdSl for ; Fri, 12 Apr 2019 12:29:24 -0400 (EDT) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 9B5B54A4A0 for ; Fri, 12 Apr 2019 12:29:24 -0400 (EDT) In-Reply-To: <1555086498-26691-1-git-send-email-Dave.Martin@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: kvmarm@lists.cs.columbia.edu Cc: Okamoto Takayuki , Christoffer Dall , Ard Biesheuvel , Marc Zyngier , Catalin Marinas , Will Deacon , Zhang Lei , Julien Grall , linux-arm-kernel@lists.infradead.org List-Id: kvmarm@lists.cs.columbia.edu sve_reg_to_region() currently passes the result of vcpu_sve_state_size() to array_index_nospec(), effectively leading to a divide / modulo operation. Currently the code bails out and returns -EINVAL if vcpu_sve_state_size() turns out to be zero, in order to avoid going ahead and attempting to divide by zero. This is reasonable, but it should only happen if the kernel contains some other bug that allowed this code to be reached without the vcpu having been properly initialised. To make it clear that this is a defence against bugs rather than something that the user should be able to trigger, this patch marks the check with WARN_ON(). Suggested-by: Andrew Jones Signed-off-by: Dave Martin --- arch/arm64/kvm/guest.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c index e45a042..73044e3 100644 --- a/arch/arm64/kvm/guest.c +++ b/arch/arm64/kvm/guest.c @@ -371,7 +371,7 @@ static int sve_reg_to_region(struct sve_state_reg_region *region, } sve_state_size = vcpu_sve_state_size(vcpu); - if (!sve_state_size) + if (WARN_ON(!sve_state_size)) return -EINVAL; region->koffset = array_index_nospec(reqoffset, sve_state_size); -- 2.1.4 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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 7A4F9C10F14 for ; Fri, 12 Apr 2019 16:29:30 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 2C3A520869 for ; Fri, 12 Apr 2019 16:29:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2C3A520869 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id C8B794A4C5; Fri, 12 Apr 2019 12:29:29 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 52qe6fVGtqlO; Fri, 12 Apr 2019 12:29:27 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id D15214A4EC; Fri, 12 Apr 2019 12:29:26 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 91BFD4A4C5 for ; Fri, 12 Apr 2019 12:29:25 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ED5OWQNKPdSl for ; Fri, 12 Apr 2019 12:29:24 -0400 (EDT) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 9B5B54A4A0 for ; Fri, 12 Apr 2019 12:29:24 -0400 (EDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2AE2C15AD; Fri, 12 Apr 2019 09:29:24 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id DAE273F718; Fri, 12 Apr 2019 09:29:21 -0700 (PDT) From: Dave Martin To: kvmarm@lists.cs.columbia.edu Subject: [PATCH 08/14] KVM: arm64/sve: WARN when avoiding divide-by-zero in sve_reg_to_region() Date: Fri, 12 Apr 2019 17:28:12 +0100 Message-Id: <1555086498-26691-9-git-send-email-Dave.Martin@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1555086498-26691-1-git-send-email-Dave.Martin@arm.com> References: <1555086498-26691-1-git-send-email-Dave.Martin@arm.com> Cc: Okamoto Takayuki , Christoffer Dall , Ard Biesheuvel , Marc Zyngier , Catalin Marinas , Will Deacon , Zhang Lei , Julien Grall , linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Message-ID: <20190412162812.l08q9wyFCoTcfCY0lrw8vXNyA1FaM3W3hCHydX5bWpI@z> sve_reg_to_region() currently passes the result of vcpu_sve_state_size() to array_index_nospec(), effectively leading to a divide / modulo operation. Currently the code bails out and returns -EINVAL if vcpu_sve_state_size() turns out to be zero, in order to avoid going ahead and attempting to divide by zero. This is reasonable, but it should only happen if the kernel contains some other bug that allowed this code to be reached without the vcpu having been properly initialised. To make it clear that this is a defence against bugs rather than something that the user should be able to trigger, this patch marks the check with WARN_ON(). Suggested-by: Andrew Jones Signed-off-by: Dave Martin --- arch/arm64/kvm/guest.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c index e45a042..73044e3 100644 --- a/arch/arm64/kvm/guest.c +++ b/arch/arm64/kvm/guest.c @@ -371,7 +371,7 @@ static int sve_reg_to_region(struct sve_state_reg_region *region, } sve_state_size = vcpu_sve_state_size(vcpu); - if (!sve_state_size) + if (WARN_ON(!sve_state_size)) return -EINVAL; region->koffset = array_index_nospec(reqoffset, sve_state_size); -- 2.1.4 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm