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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF336C433F5 for ; Wed, 17 Nov 2021 03:09:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B8E3D6108D for ; Wed, 17 Nov 2021 03:09:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231303AbhKQDL5 (ORCPT ); Tue, 16 Nov 2021 22:11:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230447AbhKQDL5 (ORCPT ); Tue, 16 Nov 2021 22:11:57 -0500 Received: from mail-wr1-x433.google.com (mail-wr1-x433.google.com [IPv6:2a00:1450:4864:20::433]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F2482C061570; Tue, 16 Nov 2021 19:08:58 -0800 (PST) Received: by mail-wr1-x433.google.com with SMTP id s13so1686909wrb.3; Tue, 16 Nov 2021 19:08:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=7UhcpsKrtyIsxTBA6QenhVurPqFsIK55Y63ymJwZ+Fo=; b=ZN3EHphS8kER4m9GoZKX4VnmOccZKxd/re2+Nz57yq/lVLPXTU+QZvlDe8LMQ+H5r4 tZc3nW7KQ1hvlw0IzDjZLcyojYbiDYJYv9EudP8AwUXQxqbCLLO2A/1ejyqG1E/wlUH8 aHtqioUWjjXnkTn21knutTwSEa/1bgJCyl01FspxsPqrMghXEwQL7OXF1Bh9gS/e69Sf awPFGVn52q4YlgfPHjbwmlpihG38fkbznvPIgn+XLRKw2AWrsnSrBnXJyda3ak7sLbCw TmiEsGzpduktEf5hP9WVlgKkV3pclXs8c7xlbvkSWLGxbK46zGQncz11fPn9cEp/CN0Z +aMg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=7UhcpsKrtyIsxTBA6QenhVurPqFsIK55Y63ymJwZ+Fo=; b=RSjRS4yk0nqR6zinURa7fXLFyYk5x/n3Bv9mOpicG23WlPf9Z8BHGFueYAllgOwZiT 5QyvE6CM+csxYrVSkdYGY0vmqlXPVF9enWQ1aKzC7KkqgnrxyL4csra1Guc8UKiAgvMT 2C2FcOjJ7+kiJRYy/h53x/u20LBvmu9y7SbGq/Bq5shjvbF40Veexu5csRtv8O41Ad94 IWO0Pl20Pjz7P/4oa69SGHj4fCv3/HvdNMZcDy3nO+P9EtGJTF/Xde0y5HWBmLZbDA5h ka6WCBQlE6riBOEEJNuB0TMG+UiOm/0IKhPUQyfbt4ZZjHLkgt/DItpcQNAaux7A+Tuk fFDQ== X-Gm-Message-State: AOAM531wfXbr2Q9VP7Qc5+8ln054lgrE90FuYXDASLVVE1pFKxGcqQbU FnmNhHWTgZrAuRbbi7w5W9irugpGSZbEvAjxKNeFGDqT9DA= X-Google-Smtp-Source: ABdhPJxcXeWlmlPMVZTnLP71dZsGRLdLEtXRpeRD39863OkYlkfI2jQI8gE+je80TT7FAJUWbe/hPpu54cymOk+zG8k= X-Received: by 2002:adf:9d82:: with SMTP id p2mr15637311wre.414.1637118537630; Tue, 16 Nov 2021 19:08:57 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Sandy Harris Date: Wed, 17 Nov 2021 11:08:45 +0800 Message-ID: Subject: Re: [PATCH 1/8] Replace memset() with memzero_explicit() To: Greg Kroah-Hartman Cc: LKML , Linux Crypto Mailing List , "David S. Miller" , Herbert Xu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org On Tue, Nov 16, 2021 at 7:51 PM Greg Kroah-Hartman wrote: > Have you looked at the output of the compiler to see if this really is > needed or not? No. To do that right you'd need to look at (at least) gcc & clang, multiple architectures (cross-compiled & native) & various levels of optimisation. I just looked at the C code. > And what exactly are you zeroing out that could be read afterward > somehow? Whatever it is, the person who wrote the code thought it was worth zeroing out with memset(). The only question is whether it is safer to use memzero_explicit(). Granted in many cases this will not matter unless the kernel is compiled at some optimisation level that does cross-function analysis so it might be "smart" enough to optimise out the memset(). Also granted it does not matter unless an attacker can look inside the running kernel & if he or she has that level of privilege, then you have much else to worry about. Still, it seemed safer to me to use memzero_explicit() in these cases.