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 CE010C433FE for ; Sun, 20 Nov 2022 01:05:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229499AbiKTBFA (ORCPT ); Sat, 19 Nov 2022 20:05:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229437AbiKTBE5 (ORCPT ); Sat, 19 Nov 2022 20:04:57 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 04F0DB6B34; Sat, 19 Nov 2022 17:04:56 -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 ams.source.kernel.org (Postfix) with ESMTPS id 9663EB8085E; Sun, 20 Nov 2022 01:04:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C67EC433D6; Sun, 20 Nov 2022 01:04:53 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="QlCx2dJr" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1668906291; 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=PwCgR4GrIDa93Xj810+SeDsgFfSgAHtSL3WBPnVichA=; b=QlCx2dJrMPKdb8FOUiyeKgxCV8ijGOybdybyPkdf3VdyyapD+FmDwtoVG1S1GfYKre1Y6q 0GMjrNNxDHhDtKQLfzg03rZciD5A/GO+u0aALfbvi92PKrsR8+KBdAbQ2cVIdv801iJXGr gUISb3oVtbe8F64xf5oNH7mo24Bgm0M= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 08b48af9 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Sun, 20 Nov 2022 01:04:51 +0000 (UTC) Date: Sun, 20 Nov 2022 02:04:49 +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 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. Jason