From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.6 required=5.0 tests=DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, T_DKIM_INVALID autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 3AD1E7D072 for ; Wed, 11 Jul 2018 21:07:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732384AbeGKVNt (ORCPT ); Wed, 11 Jul 2018 17:13:49 -0400 Received: from mail-oi0-f67.google.com ([209.85.218.67]:34299 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732500AbeGKVNt (ORCPT ); Wed, 11 Jul 2018 17:13:49 -0400 Received: by mail-oi0-f67.google.com with SMTP id 13-v6so51884432ois.1 for ; Wed, 11 Jul 2018 14:07:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=lh8TxHl5WB9OmBO9lEWZUkFPn5o9qgsioXcJ38g1tTE=; b=hPqxaqXpbNK98q6ILX77YhgMEtIeMRaBAHxQfRaKS4MJWJPHeKzWnoSGaEgLBO6ZYA FXvWA2aoDNipGQdC1MM9vCTOWbBT+zoS49ssfKtLHJWXyzZWaziigAV6fuK+CyJjoVvD UJJkbdV8zPjTLBE9yZ5/TQGqhamcXEBqL35nfKHA1UNyEGdwpuVsZuMtYmmw02vwdwvY c5c2rR04uu+LzNo52dCw6cVGvUIkFjzrzP69iFpdORFoHCadBPU20LrXbHyoJKa7md+j IN3K0PnwlSw5vtxOO/pKgvx+Aq8dDPc/x/VDbiyABDPyuikjW9LDQFgGYA5fvInVfLN1 xj6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=lh8TxHl5WB9OmBO9lEWZUkFPn5o9qgsioXcJ38g1tTE=; b=Grx1CsfFQxKcmgRZj6vb8jNqpkZWPwMZ3nqtcWwPsfRw7jpD6oPiI0uzaF8eRoCvTi LZvdEJCKV3pIbwKL9MLAvfrSh9U46l0IG+pwEKl1ueSdf0cy36QdITJ/l/KinWPNzEt6 JoX31nBTlP/YcyKPvjQdcFdAekHOQWFXaatwF75Qk2FbirIcEVtVKG0PYQ1tlAu244tb TdR/dSTxEtd/BbwuHBp6DE5j16+IBL8nxHt4qQ6axYmB8GhKpXNW5zjaO7ypNupDhPsi izQLNsOFfgqyUGMfYiWWz9MsLcqCJu921AAbqEZtWuWW8tyKlRTKqCWFivlFvOiIwL5T bpeA== X-Gm-Message-State: AOUpUlEflc0vWRHPisUwIIHkSie3CVkwTWq+sseIc7HzhzJNF3eGkb/d wNNyE9hdn+YyP/S+A06JlpBt0DhX1V3Wm7u8cz2s8Q== X-Google-Smtp-Source: AAOMgpfBBYEQ4Y+7kVB2Nlk0mE+pKHZhYC0ZSteaZ7lLy7gdT8VD4lD9jRLmD84cSuBGuFSLenyuQI+QiSHhidCTp6U= X-Received: by 2002:aca:c42:: with SMTP id i2-v6mr264102oiy.219.1531343256258; Wed, 11 Jul 2018 14:07:36 -0700 (PDT) MIME-Version: 1.0 References: <20180710222639.8241-1-yu-cheng.yu@intel.com> <20180710222639.8241-23-yu-cheng.yu@intel.com> In-Reply-To: <20180710222639.8241-23-yu-cheng.yu@intel.com> From: Jann Horn Date: Wed, 11 Jul 2018 14:07:09 -0700 Message-ID: Subject: Re: [RFC PATCH v2 22/27] x86/cet/ibt: User-mode indirect branch tracking support To: yu-cheng.yu@intel.com Cc: "the arch/x86 maintainers" , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , bsingharora@gmail.com, Cyrill Gorcunov , Dave Hansen , Florian Weimer , hjl.tools@gmail.com, Jonathan Corbet , keescook@chromiun.org, Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , ravi.v.shankar@intel.com, vedvyas.shanbhogue@intel.com Content-Type: text/plain; charset="UTF-8" Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, Jul 10, 2018 at 3:31 PM Yu-cheng Yu wrote: > > Add user-mode indirect branch tracking enabling/disabling > and supporting routines. > > Signed-off-by: H.J. Lu > Signed-off-by: Yu-cheng Yu [...] > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c > index 4eba7790c4e4..8bbd63e1a2ba 100644 > --- a/arch/x86/kernel/cet.c > +++ b/arch/x86/kernel/cet.c [...] > +static unsigned long ibt_mmap(unsigned long addr, unsigned long len) > +{ > + struct mm_struct *mm = current->mm; > + unsigned long populate; > + > + down_write(&mm->mmap_sem); > + addr = do_mmap(NULL, addr, len, PROT_READ | PROT_WRITE, > + MAP_ANONYMOUS | MAP_PRIVATE, > + VM_DONTDUMP, 0, &populate, NULL); > + up_write(&mm->mmap_sem); > + > + if (populate) > + mm_populate(addr, populate); > + > + return addr; > +} Is this thing going to stay writable? Will any process with an IBT bitmap be able to disable protections by messing with the bitmap even if the lock-out mode is active? If so, would it perhaps make sense to forbid lock-out mode if an IBT bitmap is active, to make it clear that effective lock-out is impossible in that state? -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html