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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 5B012C433E0 for ; Tue, 26 May 2020 05:05:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 28FAE207D8 for ; Tue, 26 May 2020 05:05:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="BIhrzCXi" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726598AbgEZFFH (ORCPT ); Tue, 26 May 2020 01:05:07 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:52931 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725872AbgEZFFG (ORCPT ); Tue, 26 May 2020 01:05:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1590469505; 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=Oz1sdMnNcBOEuR7TbEaLiAqhkVwdoF5waHE5jMnmydI=; b=BIhrzCXihiywmMXzUO4YLoQlDruUjWrTrIul82kKOGZ1RSsXw12aCbSL5KetwZuaIdqYmM SBrNZ91YPJY1gARmOEVauVr5Jnt7K20YJaJjVUlaIEbjKHv4k/TSGOPlXbvfbHZDRS+iqG h/q3bUyav7ckVamayMGRw6D9CcFZwcw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-299-uOahTH1bPmq4J7iQyeUFcA-1; Tue, 26 May 2020 01:05:01 -0400 X-MC-Unique: uOahTH1bPmq4J7iQyeUFcA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BDEC210082EA; Tue, 26 May 2020 05:04:59 +0000 (UTC) Received: from dhcp-128-65.nay.redhat.com (ovpn-12-170.pek2.redhat.com [10.72.12.170]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F1E501BCBE; Tue, 26 May 2020 05:04:55 +0000 (UTC) Date: Tue, 26 May 2020 13:04:51 +0800 From: Dave Young To: Lianbo Jiang Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, jbohac@suse.cz, jmorris@namei.org, mjg59@google.com, bhe@redhat.com Subject: Re: [PATCH] kexec: Do not verify the signature without the lockdown or mandatory signature Message-ID: <20200526050451.GA74334@dhcp-128-65.nay.redhat.com> References: <20200525052351.24134-1-lijiang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200525052351.24134-1-lijiang@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/25/20 at 01:23pm, Lianbo Jiang wrote: > Signature verification is an important security feature, to protect > system from being attacked with a kernel of unknown origin. Kexec > rebooting is a way to replace the running kernel, hence need be > secured carefully. > > In the current code of handling signature verification of kexec kernel, > the logic is very twisted. It mixes signature verification, IMA signature > appraising and kexec lockdown. > > If there is no KEXEC_SIG_FORCE, kexec kernel image doesn't have one of > signature, the supported crypto, and key, we don't think this is wrong, > Unless kexec lockdown is executed. IMA is considered as another kind of > signature appraising method. > > If kexec kernel image has signature/crypto/key, it has to go through the > signature verification and pass. Otherwise it's seen as verification > failure, and won't be loaded. > > Seems kexec kernel image with an unqualified signature is even worse than > those w/o signature at all, this sounds very unreasonable. E.g. If people > get a unsigned kernel to load, or a kernel signed with expired key, which > one is more dangerous? > > So, here, let's simplify the logic to improve code readability. If the > KEXEC_SIG_FORCE enabled or kexec lockdown enabled, signature verification > is mandated. Otherwise, we lift the bar for any kernel image. > > Signed-off-by: Lianbo Jiang > --- > kernel/kexec_file.c | 37 ++++++------------------------------- > 1 file changed, 6 insertions(+), 31 deletions(-) > > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c > index faa74d5f6941..e4bdf0c42f35 100644 > --- a/kernel/kexec_file.c > +++ b/kernel/kexec_file.c > @@ -181,52 +181,27 @@ void kimage_file_post_load_cleanup(struct kimage *image) > static int > kimage_validate_signature(struct kimage *image) > { > - const char *reason; > int ret; > > ret = arch_kexec_kernel_verify_sig(image, image->kernel_buf, > image->kernel_buf_len); > - switch (ret) { > - case 0: > - break; > + if (ret) { > + pr_debug("kernel signature verification failed (%d).\n", ret); > > - /* Certain verification errors are non-fatal if we're not > - * checking errors, provided we aren't mandating that there > - * must be a valid signature. > - */ > - case -ENODATA: > - reason = "kexec of unsigned image"; > - goto decide; > - case -ENOPKG: > - reason = "kexec of image with unsupported crypto"; > - goto decide; > - case -ENOKEY: > - reason = "kexec of image with unavailable key"; > - decide: > - if (IS_ENABLED(CONFIG_KEXEC_SIG_FORCE)) { > - pr_notice("%s rejected\n", reason); > + if (IS_ENABLED(CONFIG_KEXEC_SIG_FORCE)) > return ret; > - } > > - /* If IMA is guaranteed to appraise a signature on the kexec > + /* > + * If IMA is guaranteed to appraise a signature on the kexec > * image, permit it even if the kernel is otherwise locked > * down. > */ > if (!ima_appraise_signature(READING_KEXEC_IMAGE) && > security_locked_down(LOCKDOWN_KEXEC)) > return -EPERM; > - > - return 0; > - > - /* All other errors are fatal, including nomem, unparseable > - * signatures and signature check failures - even if signatures > - * aren't required. > - */ > - default: > - pr_notice("kernel signature verification failed (%d).\n", ret); > } > > - return ret; > + return 0; > } > #endif > > -- > 2.17.1 > Acked-by: Dave Young Thanks Dave