From patchwork Thu Jun 29 23:34:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Xu X-Patchwork-Id: 13297429 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 96DB1EB64D9 for ; Thu, 29 Jun 2023 23:35:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231787AbjF2XfJ (ORCPT ); Thu, 29 Jun 2023 19:35:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34928 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231824AbjF2XfB (ORCPT ); Thu, 29 Jun 2023 19:35:01 -0400 Received: from mail-oa1-x32.google.com (mail-oa1-x32.google.com [IPv6:2001:4860:4864:20::32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8FFBE2705 for ; Thu, 29 Jun 2023 16:34:59 -0700 (PDT) Received: by mail-oa1-x32.google.com with SMTP id 586e51a60fabf-1b060bce5b0so1133294fac.3 for ; Thu, 29 Jun 2023 16:34:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1688081699; x=1690673699; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=gG0p2NxJxfYPPHk57XaDb7PRgK5Ncrcc/zrK6bcWJBo=; b=V55WG+KNmomp8p6ckLhRrH+LXm07woxdK5aExRC5Ap8XBsUXarBgSTLvYxJcJOWLaH SZ94W8McRnwkd8EJtqtJiuP1Mqbaua+C+BgrqDU+dRC3HJ6HjxS4ALWXnq5izdYa0aWa TIiVjfq4PS1K8Y+0KXOb27kFxC49e6PrVjVQU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688081699; x=1690673699; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=gG0p2NxJxfYPPHk57XaDb7PRgK5Ncrcc/zrK6bcWJBo=; b=h3TIrpbOvFJASAgsmMQIhHKtOEJvkwP6TJhAU5fOv4z3XFUx+jFf2PVG4tKISVn8/I 9G0++xoTey3snLtHT5OIlbcdTSbIkYEvTeLNepiDHa4mNABWTfGCEy3iGtjfJVjw5Yvw GaDyWB056tTEro97yEUTf7/eCUCd1Hitwad0a4tCIuyAAWSNkExamSpO4wNTnBaBYl1T 7uozIP8jxGLDI/lSd994vZsVH+VueaXMBdEZnMssqT/HjWTa0M/fnGPQKjXlegI73OrU qP4Oi5K5aOpAW9Tjk1e/EDzlcxwEdIziU4mh8L2LwJMdgWIeny4Rd1DODmUeX2Kb5Zft LWvQ== X-Gm-Message-State: AC+VfDyRYQXofvATIfwQdWmGhmHoak3UxA12jP5dUMxl+0Qh08zYurEM VXNVN0z3VqHouV8E+tN2S7UopQ== X-Google-Smtp-Source: ACHHUZ4zm9+O4p+Sybi08lceONGhN6p+USDHiBG49m/rR5eMzi1I2db76dpbjYtp40INdTnI3DxXkQ== X-Received: by 2002:a05:6870:7c13:b0:1b0:432d:acb7 with SMTP id je19-20020a0568707c1300b001b0432dacb7mr1706353oab.35.1688081698833; Thu, 29 Jun 2023 16:34:58 -0700 (PDT) Received: from localhost (183.43.230.35.bc.googleusercontent.com. [35.230.43.183]) by smtp.gmail.com with UTF8SMTPSA id n59-20020a17090a2cc100b0025bdc3454c6sm12441785pjd.8.2023.06.29.16.34.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Jun 2023 16:34:58 -0700 (PDT) From: jeffxu@chromium.org To: skhan@linuxfoundation.org, keescook@chromium.org Cc: akpm@linux-foundation.org, dmitry.torokhov@gmail.com, dverkamp@chromium.org, hughd@google.com, jeffxu@google.com, jorgelo@chromium.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, jannh@google.com, linux-hardening@vger.kernel.org, linux-security-module@vger.kernel.org, Dominique Martinet Subject: [PATCH v2] Documentation: mm/memfd: vm.memfd_noexec Date: Thu, 29 Jun 2023 23:34:54 +0000 Message-ID: <20230629233454.4166842-1-jeffxu@google.com> X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog MIME-Version: 1.0 Precedence: bulk List-ID: From: Jeff Xu Add documentation for sysctl vm.memfd_noexec Link:https://lore.kernel.org/linux-mm/CABi2SkXUX_QqTQ10Yx9bBUGpN1wByOi_=gZU6WEy5a8MaQY3Jw@mail.gmail.com/T/ Reported-by: Dominique Martinet Signed-off-by: Jeff Xu --- Documentation/admin-guide/sysctl/vm.rst | 30 +++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index 45ba1f4dc004..621588041a9e 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -424,6 +424,36 @@ e.g., up to one or two maps per allocation. The default value is 65530. +memfd_noexec: +============= +This pid namespaced sysctl controls memfd_create(). + +The new MFD_NOEXEC_SEAL and MFD_EXEC flags of memfd_create() allows +application to set executable bit at creation time. + +When MFD_NOEXEC_SEAL is set, memfd is created without executable bit +(mode:0666), and sealed with F_SEAL_EXEC, so it can't be chmod to +be executable (mode: 0777) after creation. + +when MFD_EXEC flag is set, memfd is created with executable bit +(mode:0777), this is the same as the old behavior of memfd_create. + +The new pid namespaced sysctl vm.memfd_noexec has 3 values: +0: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL acts like + MFD_EXEC was set. +1: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL acts like + MFD_NOEXEC_SEAL was set. +2: memfd_create() without MFD_NOEXEC_SEAL will be rejected. + +The default value is 0. + +Once set, it can't be downgraded at runtime, i.e. 2=>1, 1=>0 +are denied. + +This is pid namespaced sysctl, child processes inherit the parent +process's memfd_noexec at the time of fork. Changes to the parent +process after fork are not automatically propagated to the child +process. memory_failure_early_kill: ==========================