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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 786D2C3DA7A for ; Sat, 31 Dec 2022 12:55:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235592AbiLaMzv (ORCPT ); Sat, 31 Dec 2022 07:55:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36626 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235583AbiLaMzq (ORCPT ); Sat, 31 Dec 2022 07:55:46 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 790B4131 for ; Sat, 31 Dec 2022 04:55:43 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 26357B80759 for ; Sat, 31 Dec 2022 12:55:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BF2C3C433D2; Sat, 31 Dec 2022 12:55:39 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="Zj+6Yeu6" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1672491338; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=WtAEE7+A30698oarN7kLZng0aHalPx3eHSCK0c4NZ4Q=; b=Zj+6Yeu6IKHkbjh3w8ulIKp0JX/VtWBFOj14CAflyHJ+n8iXBigBmLi7IeaTq0LN/SwKvo TV9V5xhqF6m/qbS4UeCrqxRQdy4gg7/2lkMvFtOC395/Sk28Aolfo81AtWtFKmIOux4I0i ZyK6onKXNIvl4UIycmmga0mTpmPM5oM= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 3a678b71 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Sat, 31 Dec 2022 12:55:38 +0000 (UTC) Date: Sat, 31 Dec 2022 13:55:32 +0100 From: "Jason A. Donenfeld" To: "H. Peter Anvin" Cc: Borislav Petkov , pbonzini@redhat.com, ebiggers@kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, ardb@kernel.org, kraxel@redhat.com, philmd@linaro.org Subject: Re: [PATCH qemu] x86: don't let decompressed kernel image clobber setup_data Message-ID: References: <46466e54-25c3-3194-8546-a57cd4a80d9d@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <46466e54-25c3-3194-8546-a57cd4a80d9d@zytor.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 30, 2022 at 05:06:55PM -0800, H. Peter Anvin wrote: > > > On 12/30/22 14:10, Jason A. Donenfeld wrote: > > On Fri, Dec 30, 2022 at 01:58:39PM -0800, H. Peter Anvin wrote: > >> See the other thread fork. They have identified the problem already. > > > > Not sure I follow. Is there another thread where somebody worked out why > > this 62meg limit was happening? > > > > Note that I sent v2/v3, to fix the original problem in a different way, > > and if that looks good to the QEMU maintainers, then we can all be happy > > with that. But I *haven't* addressed and still don't fully understand > > why the 62meg limit applied to my v1 in the way it does. Did you find a > > bug there to fix? If so, please do CC me. > > > > Yes, you yourself posted the problem: > > > Then build qemu. Run it with `-kernel bzImage`, based on the kernel > > built with the .config I attached. > > > > You'll see that the CPU triple faults when hitting this line: > > > > sd = (struct setup_data *)boot_params->hdr.setup_data; > > while (sd) { > > unsigned long sd_addr = (unsigned long)sd; > > > > kernel_add_identity_map(sd_addr, sd_addr + sizeof(*sd) + sd->len); <---- > > sd = (struct setup_data *)sd->next; > > } > > > > , because it dereferences *sd. This does not happen if the decompressed > > size of the kernel is < 62 megs. > > > > So that's the "big and pretty serious" bug that might be worthy of > > investigation. > > This needs to be something like: > > kernel_add_identity_map(sd_addr, sd_addr + sizeof(*sd)); > kernel_add_identity_map(sd_addr + sizeof(*sd), > sd_addr + sizeof(*sd) + sd->len); > Oh, right, duh. Thanks for spelling it out. Jason