From patchwork Fri Jun 30 03:25:35 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Xu X-Patchwork-Id: 13297546 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 95122C001DF for ; Fri, 30 Jun 2023 03:25:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231886AbjF3DZm (ORCPT ); Thu, 29 Jun 2023 23:25:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41392 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229459AbjF3DZk (ORCPT ); Thu, 29 Jun 2023 23:25:40 -0400 Received: from mail-pf1-x431.google.com (mail-pf1-x431.google.com [IPv6:2607:f8b0:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3BFAB35A5 for ; Thu, 29 Jun 2023 20:25:39 -0700 (PDT) Received: by mail-pf1-x431.google.com with SMTP id d2e1a72fcca58-668711086f4so884135b3a.1 for ; Thu, 29 Jun 2023 20:25:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1688095538; x=1690687538; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=gG0p2NxJxfYPPHk57XaDb7PRgK5Ncrcc/zrK6bcWJBo=; b=bWbcBjLe/HmjBUDi0chJKHI1VfwXeVHFrwoWQ6d5F3ktM+1Hx4SU0oGAk43uPUCNJS fay+/AQYi1YyouUv9X87uiVa71QR3+42BgL6odKqwm0xDf4ur4NY6vRttiQcU8fa9H7C BbtQfAx2ouVJRy+ccgkoOOaFpSGcWKEme9h7w= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688095538; x=1690687538; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=gG0p2NxJxfYPPHk57XaDb7PRgK5Ncrcc/zrK6bcWJBo=; b=b0PXrRs/7NvM9KARQrrbNBrmpYsiD0KIbGWLztr6wLt0eK7KxiaNBG99Y3H9H42JZU qQ1QF4KSg9P6Xg/87MhwFR+2zW8BW0KEusb+mQJqJdZvEZDEqsZPRtIU8P7ydNFG4jmS gxVPOYLwtn+n60q5Je4DAvU13+6dwyHa9br67lPCjiqNlh5HUMmcZg8Xk4/tEk4zYyqe ydJURyFm/We6Y32gITLdy8H4VCZAY5YTSTZpx/OslPweJFeELLVq2qhrxOKOPeU44IfI 6LFvV9HHTvQRdXqn3/TntwJbWghz4jhigaH0iIeMJEPc18YHynJcRBFoJ/GXzEw1VYw9 x4GQ== X-Gm-Message-State: AC+VfDxOBtk0xfvVFFGdTe2XKslrBmlBqM+BDpSWNxb5QY4fQcoh/VI+ ay+g0YLBidpy/mHTcWmZtDDHHg== X-Google-Smtp-Source: ACHHUZ5TBCQc99UAuCTq/sSZmqcHuuEfzJMPoZsd6eNZgMDz7INWJtHCNyWIS/wMBM2hYLOZS6QS3A== X-Received: by 2002:a05:6a00:27aa:b0:657:1fe5:eb63 with SMTP id bd42-20020a056a0027aa00b006571fe5eb63mr7433745pfb.7.1688095538633; Thu, 29 Jun 2023 20:25:38 -0700 (PDT) Received: from localhost (183.43.230.35.bc.googleusercontent.com. [35.230.43.183]) by smtp.gmail.com with UTF8SMTPSA id f4-20020aa78b04000000b0064fd4a6b306sm8973599pfd.76.2023.06.29.20.25.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Jun 2023 20:25:38 -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, asmadeus@codewreck.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 Subject: [PATCH v3 1/1] Documentation: mm/memfd: vm.memfd_noexec Date: Fri, 30 Jun 2023 03:25:35 +0000 Message-ID: <20230630032535.625390-2-jeffxu@google.com> X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog In-Reply-To: <20230630032535.625390-1-jeffxu@google.com> References: <20230630032535.625390-1-jeffxu@google.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org 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: ==========================