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 C7164C433FE for ; Mon, 21 Nov 2022 03:23:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229893AbiKUDX2 (ORCPT ); Sun, 20 Nov 2022 22:23:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229755AbiKUDX1 (ORCPT ); Sun, 20 Nov 2022 22:23:27 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B4A7618B10; Sun, 20 Nov 2022 19:23:26 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 5157A60E9F; Mon, 21 Nov 2022 03:23:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AA7D0C433C1; Mon, 21 Nov 2022 03:23:24 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="FGcmyMnA" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1669001003; 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=iHEmdgq+IRGtyRkvMHcpeJyVrJYV+YY+BtviBpbtKkE=; b=FGcmyMnAD11Sh+J4t9G3VpYMKj7qX+ijuot6gl1P6jUUjOl0wT6U3g43oAe6fszlrs6kBx CtJekQ6F9NjrzynOGtu7yfJ7JIVyT2tu+QbpXIMaZ/rrVuuMkaq1nlhrRFTgAHJp55Srgv RPRdrjHlUn754oDRoamnEDWZ5Wp6WSI= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 73f9b883 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Mon, 21 Nov 2022 03:23:22 +0000 (UTC) Date: Mon, 21 Nov 2022 04:23:20 +0100 From: "Jason A. Donenfeld" To: Eric Biggers Cc: linux-kernel@vger.kernel.org, patches@lists.linux.dev, linux-crypto@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell Subject: Re: [PATCH v5 2/3] random: introduce generic vDSO getrandom() implementation Message-ID: References: <20221119120929.2963813-1-Jason@zx2c4.com> <20221119120929.2963813-3-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 20, 2022 at 02:04:49AM +0100, Jason A. Donenfeld wrote: > On Sun, Nov 20, 2022 at 01:53:53AM +0100, Jason A. Donenfeld wrote: > > I'm not quite sure what the best approach here is. One idea would be to > > just note that libcs should wait until vgetrandom() has returned > > everywhere before forking, using its atfork functionality. > > To elaborate on this idea a bit, the way this looks is: > > rwlock_t l; > pid_t fork(void) > { > pid_t pid; > write_lock(&l); > pid = syscall_fork(); > write_unlock(&l); > return pid; > } > ssize_t getrandom(...) > { > ssize_t ret; > ... > if (!read_try_lock(&l)) > return syscall_getrandom(...); > ret = vdso_getrandom(...); > read_unlock(&l); > return ret; > } > > So maybe that doesn't seem that bad, especially considering libc already > has the kind of infrastructure in place to do that somewhat easily. > Maybe there's a priority locking thing to get right here -- the writer > should immediately starve out all future readers, so it's not unbound -- > but that seems par for the course. Fortunately none of this was necessary, and I've got things implemented without needing to resort to that, for v+1. Jason