From patchwork Wed Nov 16 16:16:36 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 625286 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 8C168C4167B for ; Wed, 16 Nov 2022 16:17:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234127AbiKPQRV (ORCPT ); Wed, 16 Nov 2022 11:17:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53970 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234776AbiKPQRB (ORCPT ); Wed, 16 Nov 2022 11:17:01 -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 B303E57B7C; Wed, 16 Nov 2022 08:16:59 -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 6A3AFB81DE0; Wed, 16 Nov 2022 16:16:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 708CFC433C1; Wed, 16 Nov 2022 16:16:56 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="L3qpjO+h" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1668615414; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=7081WT2vIv2P593Em1s6an5/PNnBOO7eRlHKQoDe8bM=; b=L3qpjO+hA//nPICVxX6CEoFke5uoMjJPXe77EoYqr8paiIG2qZARvNIxdH2kXppvCokuzO t3D6umAOT59195cQnZ3y3NYCT5LrvJad7gpDHbq++Zip2Bwpyu57wXsHEEQm0dbhOHsF/4 mIOkuGtdbh1b0ZOpC3kGn4b1D8KxeoQ= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id d4ea79a6 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Wed, 16 Nov 2022 16:16:53 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-efi@vger.kernel.org, linux-crypto@vger.kernel.org Cc: "Jason A. Donenfeld" , Ard Biesheuvel , Lennart Poettering Subject: [PATCH RFC v1 0/6] Use EFI variables for random seed Date: Wed, 16 Nov 2022 17:16:36 +0100 Message-Id: <20221116161642.1670235-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org This is a rough sketch of a proposal to use non-volatile EFI variables as random seeds for EFISTUB to manage. Patch 1 adds (back) the random.c async notifier, so we can learn when the RNG is initialized. Patch 2 uses it in vsprintf, because I promised Sebastian we'd do that if it ever gets added back for whatever reason. Patch 3 is already in efi.git and isn't new here, but is a pre-req for the next patch. Patch 4 uses the random seed from an EFI variable to pass to Linux. Patch 5 prevents the variable from being read by efivarfs. [Note: probably the legacy efifs needs updating too? Or has this been removed?] Patch 6 uses patch 1 to refresh the EFI variable when the RNG is initialized. If folks like this idea and it moves forward, 1,2,6 will be taken into my tree, and 3,4,5 will go via Ard's. Commit messages are rather sparse at the moment. I'll fill those out for the next non-RFC patchset if this idea isn't immediately demolished. The biggest consideration is wear leveling on the EFI variable flash chips. However, EFI *already* winds up writing to non-volatile memory on every single boot anyway, so maybe it's not actually a big deal? Thoughts? Cc: Ard Biesheuvel Cc: Lennart Poettering Ard Biesheuvel (1): efi: random: combine bootloader provided RNG seed with RNG protocol output Jason A. Donenfeld (5): random: add back async readiness notifier vsprintf: initialize siphash key using notifier efi: stub: use random seed from EFI variable efi: efivarfs: prohibit reading random seed variables efi: refresh non-volatile random seed when RNG is initialized drivers/char/random.c | 30 +++++++++ drivers/firmware/efi/efi.c | 14 +++++ drivers/firmware/efi/libstub/efistub.h | 2 + drivers/firmware/efi/libstub/random.c | 85 +++++++++++++++++++++++--- fs/efivarfs/file.c | 3 + include/linux/efi.h | 3 +- include/linux/random.h | 1 + lib/vsprintf.c | 14 ++--- 8 files changed, 131 insertions(+), 21 deletions(-) Reviewed-by: Petr Mladek