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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 22 Feb 2019 16:08:59 -0800
Message-ID: <CAHk-=whu_iwv4TQP5Xd62bTfWW-uswVecUbFeiSCuTWnH1xgPg@mail.gmail.com>
Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access
 kernel memory that can fault
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     David Miller <davem@davemloft.net>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        stable <stable@vger.kernel.org>,
        Changbin Du <changbin.du@gmail.com>,
        Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Andrew Lutomirski <luto@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Netdev <netdev@vger.kernel.org>, bpf@vger.kernel.org
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On Fri, Feb 22, 2019 at 3:56 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> It will preserve existing bpf_probe_read() behavior on x86.

... but that's the worst possible situation.

It appears that people haven't understood that kernel and user
addresses are distinct, and may have written programs that are
fundamentally buggy.

And we _want_ to make it clear that they are buggy on x86-64, exactly
because x86-64 is the one that gets the most testing - by far.

So if x86-64 continues working for buggy programs, then that only
means that those bugs never get fixed.

It would be much better to try to get those things fixed, and make the
x86-64 implementation stricter, exactly so that people end up
_realizing_ that they can't just think "a pointer is a pointer, and
the context doesn't matter".

From a pure functional safety standpoint, I thought bpf already knew
what kind of a pointer it had?

                   Linus