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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 8402DC43381 for ; Fri, 22 Feb 2019 23:16:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5118D2070D for ; Fri, 22 Feb 2019 23:16:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727201AbfBVXQL (ORCPT ); Fri, 22 Feb 2019 18:16:11 -0500 Received: from shards.monkeyblade.net ([23.128.96.9]:59654 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725774AbfBVXQK (ORCPT ); Fri, 22 Feb 2019 18:16:10 -0500 Received: from localhost (unknown [IPv6:2601:601:9f80:35cd::bf5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 47A7414AD91EC; Fri, 22 Feb 2019 15:16:09 -0800 (PST) Date: Fri, 22 Feb 2019 15:16:06 -0800 (PST) Message-Id: <20190222.151606.344940961752699587.davem@davemloft.net> To: jannh@google.com Cc: alexei.starovoitov@gmail.com, torvalds@linux-foundation.org, mhiramat@kernel.org, rostedt@goodmis.org, luto@amacapital.net, linux-kernel@vger.kernel.org, mingo@kernel.org, akpm@linux-foundation.org, stable@vger.kernel.org, changbin.du@gmail.com, keescook@chromium.org, luto@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault From: David Miller In-Reply-To: References: <20190222225103.o5rr5zr4fq77jdg4@ast-mbp.dhcp.thefacebook.com> X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Fri, 22 Feb 2019 15:16:09 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jann Horn Date: Sat, 23 Feb 2019 00:11:58 +0100 > I think what Linus is saying is: There are some scenarios (like a > system with the old 4G/4G X86 patch) where *the same* address can > refer to two different pieces of memory, depending on whether you > interpret it as a kernel pointer or a user pointer. Exactly. On sparc64 the kernel is mapped exactly at the same virtual addresses as userspace processes usually are mapped, even 32-bit ones. The difference is the MMU context only.