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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 4CB97C8300B for ; Thu, 30 Apr 2020 10:59:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 27D8220784 for ; Thu, 30 Apr 2020 10:59:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588244351; bh=XdmvD3Q8v1cVOjovGFmT69sCbDPOc3huwohLmrMo6aQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Jh6A9wmHizZ20JsjkWJr3fi2yu7igHA7RefJxrOQhyzGwM2ePZNpxDxFtaTqFdmKL xnMysqpdJcdHzkdd4DEVN/2lpDXwsfNDGaC0tLiYVrWbbuJjsEcDvupuQX9/XvMStC Iz8QLbTfkDYjjrZGMpxHFYLqCNetgfVolPLdo6TQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726780AbgD3K7K (ORCPT ); Thu, 30 Apr 2020 06:59:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:60842 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725280AbgD3K7I (ORCPT ); Thu, 30 Apr 2020 06:59:08 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C00E020784; Thu, 30 Apr 2020 10:59:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588244347; bh=XdmvD3Q8v1cVOjovGFmT69sCbDPOc3huwohLmrMo6aQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=LRDP7EhDi2XJ8/Y4BDNiUv0rMndR1qZec3TsYLk7z/Ujv4RPCejiqk103Qoxyx0P8 eRTj5qEqmYG1Dnf0qLKUP44Xj1w22cvWXI4/77S4iGghNXnP7yK6uttQGo2EkGVY43 PbWiUJKCvbMKaWQoRDSEJwzNzZVj02UZlJu8+eB0= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jU6uH-0080A8-UU; Thu, 30 Apr 2020 11:59:06 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 30 Apr 2020 11:59:05 +0100 From: Marc Zyngier To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, James Morse , Julien Thierry , Suzuki K Poulose Subject: Re: [PATCH] KVM: arm64: Fix 32bit PC wrap-around In-Reply-To: <20200430102556.GE19932@willie-the-truck> References: <20200430101513.318541-1-maz@kernel.org> <20200430102556.GE19932@willie-the-truck> User-Agent: Roundcube Webmail/1.4.3 Message-ID: <897baec2a3fad776716bccf3027340fa@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: will@kernel.org, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2020-04-30 11:25, Will Deacon wrote: > On Thu, Apr 30, 2020 at 11:15:13AM +0100, Marc Zyngier wrote: >> In the unlikely event that a 32bit vcpu traps into the hypervisor >> on an instruction that is located right at the end of the 32bit >> range, the emulation of that instruction is going to increment >> PC past the 32bit range. This isn't great, as userspace can then >> observe this value and get a bit confused. >> >> Conversly, userspace can do things like (in the context of a 64bit >> guest that is capable of 32bit EL0) setting PSTATE to AArch64-EL0, >> set PC to a 64bit value, change PSTATE to AArch32-USR, and observe >> that PC hasn't been truncated. More confusion. >> >> Fix both by: >> - truncating PC increments for 32bit guests >> - sanitize PC every time a core reg is changed by userspace, and >> that PSTATE indicates a 32bit mode. > > It's not clear to me whether this needs a cc stable. What do you think? > I > suppose that it really depends on how confused e.g. QEMU gets. It isn't so much QEMU itself that I'm worried about (the emulation shouldn't really care about the PC), but the likes of GDB. So yes, a cc stable seems to be in order. > >> Signed-off-by: Marc Zyngier >> --- >> arch/arm64/kvm/guest.c | 4 ++++ >> virt/kvm/arm/hyp/aarch32.c | 8 ++++++-- >> 2 files changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c >> index 23ebe51410f0..2a159af82429 100644 >> --- a/arch/arm64/kvm/guest.c >> +++ b/arch/arm64/kvm/guest.c >> @@ -200,6 +200,10 @@ static int set_core_reg(struct kvm_vcpu *vcpu, >> const struct kvm_one_reg *reg) >> } >> >> memcpy((u32 *)regs + off, valp, KVM_REG_SIZE(reg->id)); >> + >> + if (*vcpu_cpsr(vcpu) & PSR_AA32_MODE_MASK) >> + *vcpu_pc(vcpu) = lower_32_bits(*vcpu_pc(vcpu)); > > It seems slightly odd to me that we don't enforce this for *all* the > registers when running as a 32-bit guest. Couldn't userspace be equally > confused by a 64-bit lr or sp? Fair point. How about this on top, which wipes the upper 32 bits for each and every register in the current mode: diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c index 2a159af82429..f958c3c7bf65 100644 --- a/arch/arm64/kvm/guest.c +++ b/arch/arm64/kvm/guest.c @@ -201,9 +201,12 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg) memcpy((u32 *)regs + off, valp, KVM_REG_SIZE(reg->id)); - if (*vcpu_cpsr(vcpu) & PSR_AA32_MODE_MASK) - *vcpu_pc(vcpu) = lower_32_bits(*vcpu_pc(vcpu)); + if (*vcpu_cpsr(vcpu) & PSR_AA32_MODE_MASK) { + int i; + for (i = 0; i < 16; i++) + *vcpu_reg32(vcpu, i) = (u32)*vcpu_reg32(vcpu, i); + } out: return err; } I'm tempted to make the whole SET_REG hunk a separate patch though. Thanks, M. -- Jazz is not dead. It just smells funny...