netdev - Re: [PATCH RFC] bpf: Add support for reading user pointers

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Message-ID: <20190503135426.GA2606@hirez.programming.kicks-ass.net>
Date:   Fri, 3 May 2019 15:54:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Qais Yousef <qais.yousef@....com>, linux-kernel@...r.kernel.org,
        Michal Gregorczyk <michalgr@...e.com>,
        Adrian Ratiu <adrian.ratiu@...labora.com>,
        Mohammad Husain <russoue@...il.com>,
        Srinivas Ramana <sramana@...eaurora.org>,
        duyuchao <yuchao.du@...soc.com>,
        Manjo Raja Rao <linux@...ojrajarao.com>,
        Karim Yaghmour <karim.yaghmour@...rsys.com>,
        Tamir Carmeli <carmeli.tamir@...il.com>,
        Yonghong Song <yhs@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Brendan Gregg <brendan.d.gregg@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>, kernel-team@...roid.com,
        Daniel Borkmann <daniel@...earbox.net>,
        Ingo Molnar <mingo@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH RFC] bpf: Add support for reading user pointers

On Fri, May 03, 2019 at 09:49:35AM -0400, Joel Fernandes wrote:
> In
> particular, we learnt with extensive discussions that user/kernel pointers
> are not necessarily distinguishable purely based on their address.

This is correct; a number of architectures have a completely separate
user and kernel address space. Much like how the old i386 4G:4G patches
worked.