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=-5.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,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 A0B51C433E1 for ; Mon, 24 Aug 2020 21:10:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5FB522067C for ; Mon, 24 Aug 2020 21:10:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598303428; bh=b+iTlV4khAeSnNkrYWDltD8Uy3YAJwyRMXjJv/hiPYg=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=wDW9HWMjF0pm6gsTAUXoFuYUJWssqg+P0T0YR6cyXRndx2j8lRBWSNXt3Gb8BJeXJ njlXAq3y7LRMBBnIwAt+Tpr+Q6sBatSPHFpU7X6mFADT+SwjGnqNdmvxYQhL+Ds6q/ xFoYCwQw8aiHvYhzJqv0PSf7xDmNdArMFJB7UWOk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727060AbgHXVK1 (ORCPT ); Mon, 24 Aug 2020 17:10:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:42362 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726138AbgHXVK0 (ORCPT ); Mon, 24 Aug 2020 17:10:26 -0400 Received: from mail-wr1-f46.google.com (mail-wr1-f46.google.com [209.85.221.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id DE4B42067C for ; Mon, 24 Aug 2020 21:10:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598303426; bh=b+iTlV4khAeSnNkrYWDltD8Uy3YAJwyRMXjJv/hiPYg=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=yhEtqZ2KhMRVW0ugCZ7+yBbW7Rru6i8YBIawZxecusPj3pn8Z/cSpLq9hkV5Lr6SF ksTcfY4lsUKzlLGjwO82EWogdV0xfR/xwpOGxQljOuFFDbK8z8iukLiw6nP2D/fs/I reOY7S8NxKdqKAlIbHX9oN1s1fIY7cOHBWYmJA1Q= Received: by mail-wr1-f46.google.com with SMTP id l2so10534157wrc.7 for ; Mon, 24 Aug 2020 14:10:25 -0700 (PDT) X-Gm-Message-State: AOAM5323gX8yfZhqmQwZHGt20UvaExLRwN5uQTAlkCLxGyvEOoIQBjjf 9Bd7iPwSNa6UVl+Jgax1CgLOa8on5l/04HWIRIPW7Q== X-Google-Smtp-Source: ABdhPJyUkd1o3GT1Xad0KTVsiy6YUHXaldUk6yXHUKz5yS4PycBxxsVaNUIYEAOkQzrdJZlCIFg6oFgKse2fzJ0lRiE= X-Received: by 2002:a05:6000:10c6:: with SMTP id b6mr7336388wrx.257.1598303424431; Mon, 24 Aug 2020 14:10:24 -0700 (PDT) MIME-Version: 1.0 References: <7DF88F22-0310-40C9-9DA6-5EBCB4877933@amacapital.net> In-Reply-To: <7DF88F22-0310-40C9-9DA6-5EBCB4877933@amacapital.net> From: Andy Lutomirski Date: Mon, 24 Aug 2020 14:10:12 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [REGRESSION] x86/cpu fsgsbase breaks TLS in 32 bit rr tracees on a 64 bit system To: "Robert O'Callahan" Cc: "Bae, Chang Seok" , Kyle Huey , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , Andi Kleen , "Shankar, Ravi V" , LKML , "Hansen, Dave" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 22, 2020 at 6:19 AM Andy Lutomirski wrote: > > We can give you a new ptrace operation to load the selector and deduce the base from the descriptor table if it would help. Concretely, we could add one of these: PTRACE_READ_SEGMENT_DESCRIPTOR to read a segment descriptor. PTRACE_SET_FS / PTRACE_SET_GS: Sets FS or GS and updates the base accordingly. PTRACE_READ_SEGMENT_BASE: pass in a segment selector, get a base out. You would use this to populate the base fields. or perhaps a ptrace SETREGS variant that tries to preserve the old base semantics and magically sets the bases to match the selectors if the selectors are nonzero. Do any of these choices sound preferable to any of you? --Andhy