From patchwork Sat Nov 19 13:42:59 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: 626909 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 21BFBC4332F for ; Sat, 19 Nov 2022 13:43:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231445AbiKSNnQ (ORCPT ); Sat, 19 Nov 2022 08:43:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46822 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229592AbiKSNnP (ORCPT ); Sat, 19 Nov 2022 08:43:15 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC72B83EBB for ; Sat, 19 Nov 2022 05:43:14 -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 6EF2C60A6E for ; Sat, 19 Nov 2022 13:43:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2D05C433C1; Sat, 19 Nov 2022 13:43:12 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="L8WRt3rP" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1668865390; 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=sNjUH9YYxs+T2CdAZKiMZPcLV7XYZEO0+q+grRvvYi4=; b=L8WRt3rP4VI0qjaFz/qNoRuPGBNx2gAsLFnfX3DnrIESuFcJRwcsCZ9WhrJQMa1HDwnL/Z LiAGpAKRj8xNXHR1gdhjgUE7xJzVcS30+RIfvxU44ADRT2mjluJDleUEioHQpdqggTPiZ9 H5QG88aPU81HyRr2ExLRq8KnvIrSSio= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 8e760f35 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Sat, 19 Nov 2022 13:43:10 +0000 (UTC) From: "Jason A. Donenfeld" To: herbert@gondor.apana.org.au, linux-crypto@vger.kernel.org Cc: "Jason A. Donenfeld" , Andrej Shadura , Jiri Kosina Subject: [PATCH] hwrng: u2fzero - account for high quality RNG Date: Sat, 19 Nov 2022 14:42:59 +0100 Message-Id: <20221119134259.2969204-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org The U2F zero apparently has a real TRNG in it with maximum quality, not one with quality of "1", which was likely a misinterpretation of the field as a boolean. So remove the assignment entirely, so that we get the default quality setting. In the u2f-zero firmware, the 0x21 RNG command used by this driver is handled as such [1]: case U2F_CUSTOM_GET_RNG: if (atecc_send_recv(ATECC_CMD_RNG,ATECC_RNG_P1,ATECC_RNG_P2, NULL, 0, appdata.tmp, sizeof(appdata.tmp), &res) == 0 ) { memmove(msg->pkt.init.payload, res.buf, 32); U2FHID_SET_LEN(msg, 32); usb_write((uint8_t*)msg, 64); } else { U2FHID_SET_LEN(msg, 0); usb_write((uint8_t*)msg, 64); } This same call to `atecc_send_recv(ATECC_CMD_RNG,ATECC_RNG_P1, ATECC_RNG_P2,...)` is then also used in the token's cryptographically critical "u2f_new_keypair" function, as its rather straightforward source of random bytes [2]: int8_t u2f_new_keypair(uint8_t * handle, uint8_t * appid, uint8_t * pubkey) { struct atecc_response res; uint8_t private_key[36]; int i; watchdog(); if (atecc_send_recv(ATECC_CMD_RNG,ATECC_RNG_P1,ATECC_RNG_P2, NULL, 0, appdata.tmp, sizeof(appdata.tmp), &res) != 0 ) { return -1; } So it seems rather plain that the ATECC RNG is considered to provide good random numbers. [1] https://github.com/conorpp/u2f-zero/blob/master/firmware/src/custom.c [2] https://github.com/conorpp/u2f-zero/blob/master/firmware/src/u2f_atecc.c Cc: Andrej Shadura Cc: Jiri Kosina Cc: Herbert Xu Signed-off-by: Jason A. Donenfeld --- drivers/hid/hid-u2fzero.c | 1 - 1 file changed, 1 deletion(-) diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c index ad489caf53ad..744a91e6e78c 100644 --- a/drivers/hid/hid-u2fzero.c +++ b/drivers/hid/hid-u2fzero.c @@ -261,7 +261,6 @@ static int u2fzero_init_hwrng(struct u2fzero_device *dev, dev->hwrng.name = dev->rng_name; dev->hwrng.read = u2fzero_rng_read; - dev->hwrng.quality = 1; return devm_hwrng_register(&dev->hdev->dev, &dev->hwrng); }