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=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 CCFA5C433DB for ; Thu, 21 Jan 2021 16:08:16 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 4E16B23A1E for ; Thu, 21 Jan 2021 16:08:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E16B23A1E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57168 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l2cVK-0005io-VY for qemu-devel@archiver.kernel.org; Thu, 21 Jan 2021 11:08:14 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:36120) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l2cSj-0003E9-IB for qemu-devel@nongnu.org; Thu, 21 Jan 2021 11:05:34 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:31343) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l2cSh-00079c-Jy for qemu-devel@nongnu.org; Thu, 21 Jan 2021 11:05:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611245130; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Q7sHcYJWAuwxKKB5ZBc2tCcPKZrODA/OFK772/5ZYrs=; b=NLBbduGOgV4BJO1tYQ9P65bD7KEG9NYz1UWge53H0++w+ueR3UDvAw7P0kjIBWOgySAYEH vDkO3l3q6LkEsRPOTJVM6sWbyJglwxEKtj4/vR6obn3qUgxy0fBgHv6VU1iztNXMLECXCb 8w7YP8hYMrSS60alu/OGwAl5d/ueYsA= 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-372-QIIK9m2ENB-javMOnvLfkQ-1; Thu, 21 Jan 2021 11:05:27 -0500 X-MC-Unique: QIIK9m2ENB-javMOnvLfkQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4A46EA0CAB for ; Thu, 21 Jan 2021 16:05:26 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-115-169.ams2.redhat.com [10.36.115.169]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2DD296EF50; Thu, 21 Jan 2021 16:05:18 +0000 (UTC) Subject: Re: Thread safety of coroutine-sigaltstack To: Max Reitz , "qemu-devel@nongnu.org" References: <7b8155ad-0942-dc1c-f43c-bb5eb518a278@redhat.com> <445268c9-d91f-af5a-3d7e-f4c6f014ca52@redhat.com> <62d5d33c-fe2a-228b-146d-632c84d09fd5@redhat.com> <823a843f-af47-f091-1bd1-e33487524eb9@redhat.com> From: Laszlo Ersek Message-ID: <47c2c4de-7f8e-e64b-452e-e7b0f3e9d48d@redhat.com> Date: Thu, 21 Jan 2021 17:05:17 +0100 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=lersek@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=lersek@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.168, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 01/21/21 16:42, Max Reitz wrote: > Perhaps we have the policy of “If another process can send signals, then > we consider it to have full control over qemu, like a debugger.” That's what I had more or less in mind, yes; see e.g. https://man7.org/linux/man-pages/man2/ptrace.2.html EPERM The specified process cannot be traced. This could be because the tracer has insufficient privileges (the required capability is CAP_SYS_PTRACE); unprivileged processes cannot trace processes that they cannot send signals to or those running set-user-ID/set-group-ID programs, for obvious reasons. Alternatively, the process may already be being traced, or (on kernels before 2.6.26) be init(1) (PID 1). Which seems to imply that, if you can send a signal, you can ptrace() the signalee as well. (I realize that what I'm saying does not follow from *pure logic*, as the manual is stating !sendsig -> !trace, hence trace -> sendsig. Whereas we're discussing the opposite direction: sendsig -> trace. *But*, IMO, that direction is *suggested* by the manual.) Anyway, this is kind of moot; I'm OK with the mutex too. :) Thanks Laszlo