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 D79D8EE49AC for ; Tue, 22 Aug 2023 09:10:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230313AbjHVJKS (ORCPT ); Tue, 22 Aug 2023 05:10:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49934 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234075AbjHVJKQ (ORCPT ); Tue, 22 Aug 2023 05:10:16 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6384A1BE; Tue, 22 Aug 2023 02:10:13 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E6B2E64FE4; Tue, 22 Aug 2023 09:10:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8B12BC433C7; Tue, 22 Aug 2023 09:10:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692695412; bh=pQisISmZ66AdEx39jJ4009uh0Yx/8HETEG0JPihLCHM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dt1q16xZ4wVawYqxKyc7pTbYu+xIoHKLpdt4WziTYiykP4mBCSsx9VyKV3nGdWZuB CGlsfHp0LveeO9NIsm2e6txPBhrMJk1AjqMm2owxcsfgIRV8U6Tt291oP3dqGDBQwG gDHLPYuO5I1KGNzPSmFaAQ13Ck4sdojjeTz3R2DLhRG6otJRWx1AbClFee5WLwQArS PEQ+W/rcU+hY/C9pH9HW980wqKbHfsBj2syDGyGfJ4KcbpYfg7B6yf6QcxIUaEjVGF QYWB8QtIcGfFThWJC6mqnrDF7sLKwARR06oIWqrbVYOF+L5uhBGCzY8GFgI7AqFe2D prG6ZSWsJIrdA== Date: Tue, 22 Aug 2023 11:10:06 +0200 From: Christian Brauner To: Aleksa Sarai Cc: Andrew Morton , Shuah Khan , Jeff Xu , Kees Cook , Daniel Verkamp , Dominique Martinet , stable@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v2 3/5] memfd: improve userspace warnings for missing exec-related flags Message-ID: <20230822-seenotrettung-bungalow-a4ea576f6f85@brauner> References: <20230814-memfd-vm-noexec-uapi-fixes-v2-0-7ff9e3e10ba6@cyphar.com> <20230814-memfd-vm-noexec-uapi-fixes-v2-3-7ff9e3e10ba6@cyphar.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230814-memfd-vm-noexec-uapi-fixes-v2-3-7ff9e3e10ba6@cyphar.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 14, 2023 at 06:40:59PM +1000, Aleksa Sarai wrote: > In order to incentivise userspace to switch to passing MFD_EXEC and > MFD_NOEXEC_SEAL, we need to provide a warning on each attempt to call > memfd_create() without the new flags. pr_warn_once() is not useful > because on most systems the one warning is burned up during the boot > process (on my system, systemd does this within the first second of > boot) and thus userspace will in practice never see the warnings to push > them to switch to the new flags. > > The original patchset[1] used pr_warn_ratelimited(), however there were > concerns about the degree of spam in the kernel log[2,3]. The resulting > inability to detect every case was flagged as an issue at the time[4]. > > While we could come up with an alternative rate-limiting scheme such as > only outputting the message if vm.memfd_noexec has been modified, or > only outputting the message once for a given task, these alternatives > have downsides that don't make sense given how low-stakes a single > kernel warning message is. Switching to pr_info_ratelimited() instead > should be fine -- it's possible some monitoring tool will be unhappy > with a stream of warning-level messages but there's already plenty of > info-level message spam in dmesg. > > [1]: https://lore.kernel.org/20221215001205.51969-4-jeffxu@google.com/ > [2]: https://lore.kernel.org/202212161233.85C9783FB@keescook/ > [3]: https://lore.kernel.org/Y5yS8wCnuYGLHMj4@x1n/ > [4]: https://lore.kernel.org/f185bb42-b29c-977e-312e-3349eea15383@linuxfoundation.org/ > > Cc: stable@vger.kernel.org # v6.3+ > Fixes: 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC") > Signed-off-by: Aleksa Sarai > --- Reviewed-by: Christian Brauner