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 X-Spam-Level: X-Spam-Status: No, score=-4.7 required=3.0 tests=DATE_IN_PAST_96_XX, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AAED0C2D0EE for ; Sat, 28 Mar 2020 16:43:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C425206F6 for ; Sat, 28 Mar 2020 16:43:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727910AbgC1Qnz (ORCPT ); Sat, 28 Mar 2020 12:43:55 -0400 Received: from mx.sdf.org ([205.166.94.20]:49939 "EHLO mx.sdf.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727828AbgC1Qno (ORCPT ); Sat, 28 Mar 2020 12:43:44 -0400 Received: from sdf.org (IDENT:lkml@sdf.lonestar.org [205.166.94.16]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 02SGhMAI029531 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Sat, 28 Mar 2020 16:43:22 GMT Received: (from lkml@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 02SGhMtr029198; Sat, 28 Mar 2020 16:43:22 GMT Message-Id: <202003281643.02SGhMtr029198@sdf.org> From: George Spelvin Date: Tue, 10 Dec 2019 10:45:27 -0500 Subject: [RFC PATCH v1 39/50] arm: kexec_file: Avoid temp buffer for RNG seed To: linux-kernel@vger.kernel.org, lkml@sdf.org Cc: Hsin-Yi Wang , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org After using get_random_bytes(), you want to wipe the buffer afterward so the seed remains secret. In this case, we can eliminate the temporary buffer entirely. fdt_setprop_placeholder returns a pointer to the property value buffer, allowing us to put the random data directy in there without using a temporary buffer at all. Faster and less stack all in one. Signed-off-by: George Spelvin Cc: Hsin-Yi Wang Cc: Catalin Marinas Cc: Will Deacon Cc: linux-arm-kernel@lists.infradead.org --- arch/arm64/kernel/machine_kexec_file.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c index 7b08bf9499b6b..69e25bb96e3fb 100644 --- a/arch/arm64/kernel/machine_kexec_file.c +++ b/arch/arm64/kernel/machine_kexec_file.c @@ -106,12 +106,12 @@ static int setup_dtb(struct kimage *image, /* add rng-seed */ if (rng_is_initialized()) { - u8 rng_seed[RNG_SEED_SIZE]; - get_random_bytes(rng_seed, RNG_SEED_SIZE); - ret = fdt_setprop(dtb, off, FDT_PROP_RNG_SEED, rng_seed, - RNG_SEED_SIZE); + void *rng_seed; + ret = fdt_setprop_placeholder(dtb, off, FDT_PROP_RNG_SEED, + RNG_SEED_SIZE, &rng_seed); if (ret) goto out; + get_random_bytes(rng_seed, RNG_SEED_SIZE); } else { pr_notice("RNG is not initialised: omitting \"%s\" property\n", FDT_PROP_RNG_SEED); -- 2.26.0