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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A9929D2A526 for ; Wed, 16 Oct 2024 15:17:44 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t15lg-0004Ip-4T; Wed, 16 Oct 2024 11:16:56 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t15ld-0004IL-9h for qemu-devel@nongnu.org; Wed, 16 Oct 2024 11:16:53 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t15la-0007kP-Pl for qemu-devel@nongnu.org; Wed, 16 Oct 2024 11:16:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1729091807; h=from:from:reply-to: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=FyeVLZyb941Jued/kL1pbRnq+bk/AMCHCZeNDv3p4Uc=; b=Ike/HmCPfZU2/HWbH2XoUc+R6kuU/T3Hd4JP6NNds16c+4r7PSLD0uFTNjj/x2IUvMXP7Q q+bphk61XMVA8L/+6W7n/z0pelTC/UyZzxAdyEd0B6GFk6XCDeYOyQWFqCMoO3mSJ9K0UQ 1o6ZQtWa5npcTT19mR8TcgYK5rLeBjg= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-199-2N3EphTsPriCGxh-OmB6iw-1; Wed, 16 Oct 2024 11:16:45 -0400 X-MC-Unique: 2N3EphTsPriCGxh-OmB6iw-1 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9EA97195604F; Wed, 16 Oct 2024 15:16:44 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.95]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5510F19560A3; Wed, 16 Oct 2024 15:16:42 +0000 (UTC) Date: Wed, 16 Oct 2024 16:16:39 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Stefan Berger Cc: qemu-devel@nongnu.org, marcandre.lureau@gmail.com Subject: Re: [PATCH v3 2/2] tpm_emulator: Read control channel response in 2 passes Message-ID: References: <20241016145708.1166471-1-stefanb@linux.ibm.com> <20241016145708.1166471-3-stefanb@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20241016145708.1166471-3-stefanb@linux.ibm.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.038, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Oct 16, 2024 at 10:57:08AM -0400, Stefan Berger wrote: > Error responses from swtpm are typically only 4 bytes long with the > exception of a few commands that return more bytes. Therefore, read the > entire response in 2 passes and stop if the first few bytes indicate an > error response with no subsequent bytes readable. Read the rest in a 2nd > pass, if needed. This avoids getting stuck while waiting for too many > bytes. The 'getting stuck' condition has not been observed in practice so > far, though. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2615 > Signed-off-by: Stefan Berger > --- > backends/tpm/tpm_emulator.c | 65 ++++++++++++++++++++++++++++--------- > 1 file changed, 49 insertions(+), 16 deletions(-) > > diff --git a/backends/tpm/tpm_emulator.c b/backends/tpm/tpm_emulator.c > index b0e2fb3fc7..dfb298a16d 100644 > --- a/backends/tpm/tpm_emulator.c > +++ b/backends/tpm/tpm_emulator.c > @@ -123,12 +123,17 @@ static const char *tpm_emulator_strerror(uint32_t tpm_result) > } > > static int tpm_emulator_ctrlcmd(TPMEmulator *tpm, unsigned long cmd, void *msg, > - size_t msg_len_in, size_t msg_len_out) > + size_t msg_len_in, size_t msg_len_out_err, > + size_t msg_len_out_total) > { > CharBackend *dev = &tpm->ctrl_chr; > uint32_t cmd_no = cpu_to_be32(cmd); > ssize_t n = sizeof(uint32_t) + msg_len_in; > + size_t left_to_read = msg_len_out_total; > uint8_t *buf = NULL; > + ptm_res res; > + off_t o = 0; > + int to_read; > > WITH_QEMU_LOCK_GUARD(&tpm->mutex) { > buf = g_alloca(n); > @@ -140,11 +145,28 @@ static int tpm_emulator_ctrlcmd(TPMEmulator *tpm, unsigned long cmd, void *msg, > return -1; > } > > - if (msg_len_out != 0) { > - n = qemu_chr_fe_read_all(dev, msg, msg_len_out); > + if (msg_len_out_err > 0) { > + to_read = msg_len_out_err; > + } else { > + to_read = left_to_read; > + } > + while (to_read > 0) { > + n = qemu_chr_fe_read_all(dev, (uint8_t *)msg + o, to_read); > if (n <= 0) { > return -1; > } > + left_to_read -= n; > + if (left_to_read == 0) { > + return 0; > + } > + /* result error code is always in the first 4 bytes */ > + memcpy(&res, msg, sizeof(res)); > + if (res) { > + return 0; > + } > + > + o = to_read; > + to_read = left_to_read; > } Using qemu_chr_fe_read_all in a loop feels like an anti-pattern, since it will always read exactly the full amount you ask, or return an error. IOW, there code here is a rather confusing way to do exactly 2 reads of the required size. I think it'd be much clearer to just read in two steps, without a loop like this: n = qemu_chr_fe_read_all(dev, (uint8_t *)msg, msg_len_out_err); if (n != msg_len_out_err) { return -1; } /* result error code is always in the first 4 bytes */ memcpy(&res, msg, sizeof(res)); if (res) { return 0; } assert(msg_len_out_err <= msg_len_out_total); msg_len_out_total -= msg_len_out_err; n = qemu_chr_fe_read_all(dev, (uint8_t *)msg + msg_len_out_err, msg_len_out_total); if (n != msg_len_out_total) { return -1; } return 0; With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|