From: David Miller <davem@davemloft.net>
To: torvalds@linux-foundation.org
Cc: alexei.starovoitov@gmail.com, 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, jannh@google.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
Date: Fri, 22 Feb 2019 13:38:42 -0800 (PST) [thread overview]
Message-ID: <20190222.133842.1637029078039923178.davem@davemloft.net> (raw)
In-Reply-To: <CAHk-=wib9VSbwbS+N82ZPNtvt4vrvYyHyQduhFimX8nyjCyZyA@mail.gmail.com>
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 22 Feb 2019 13:20:58 -0800
> On Fri, Feb 22, 2019 at 11:27 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
>>
>> On bpf side the bpf_probe_read() helper just calls probe_kernel_read()
>> and users pass both user and kernel addresses into it and expect
>> that the helper will actually try to read from that address.
>
> As mentioned earlier in the thread, that's actually fundamentally broken.
>
> There are architectures that have physically separate address spaces,
> with the same pointer value in both kernel and user space.
>
> They are rare, but they exist. At least sparc32 and the old 4G:4G split x86.
And sparc64.
> So a pointer really should always unambiguously always be explicitly
> _either_ a kernel pointer, or a user pointer. You can't have "this is
> a pointer", and then try to figure it out by looking at the value.
> That may happen to work on x86-64, but it's literally a "happen to
> work on the most common architectures", not a design thing.
Don't be surprised if we see more separation like this in the future too.
So it's not a smart thing to code against even if you can discount all of
the examples Linus gives above.
next prev parent reply other threads:[~2019-02-22 21:38 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAHk-=wgJzNp0R3cVhjBPHTR4X9sOvHdqK4UVFfbsOKQ6L=A_eQ@mail.gmail.com>
[not found] ` <CAHk-=wh9XrOykA5J9RQ7zaBio-S_D+1AE+rGnBYWSd==pCXh+w@mail.gmail.com>
[not found] ` <20190219111802.1d6dbaa3@gandalf.local.home>
[not found] ` <CAHk-=wgTuK3kAduP-gr10vykT1uG=B2VpdffvmyBuTQ1UxPpMg@mail.gmail.com>
[not found] ` <20190219140330.5dd9e876@gandalf.local.home>
[not found] ` <20190220171019.5e81a4946b56982f324f7c45@kernel.org>
[not found] ` <20190220094926.0ab575b3@gandalf.local.home>
[not found] ` <20190222172745.2c7205d62003c0a858e33278@kernel.org>
[not found] ` <20190222173509.88489b7c5d1bf0e2ec2382ee@kernel.org>
[not found] ` <CAHk-=whNf_n1WXWW+ugAVeL5ZK0GcEP3cTYocju1nS85VtMjjQ@mail.gmail.com>
2019-02-22 19:27 ` [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault Alexei Starovoitov
2019-02-22 19:30 ` Steven Rostedt
2019-02-22 19:34 ` Alexei Starovoitov
2019-02-22 19:39 ` Steven Rostedt
2019-02-22 19:55 ` Andy Lutomirski
2019-02-22 21:43 ` Jann Horn
2019-02-22 22:08 ` Nadav Amit
2019-02-22 22:17 ` Jann Horn
2019-02-22 22:21 ` Nadav Amit
2019-02-22 22:39 ` Nadav Amit
2019-02-22 23:02 ` Jann Horn
2019-02-22 23:22 ` Nadav Amit
2019-02-22 23:59 ` Andy Lutomirski
2019-02-23 0:03 ` Alexei Starovoitov
2019-02-23 0:15 ` Nadav Amit
2019-02-24 19:35 ` Andy Lutomirski
2019-02-25 13:36 ` Masami Hiramatsu
2019-02-22 21:20 ` Linus Torvalds
2019-02-22 21:38 ` David Miller [this message]
2019-02-22 21:59 ` Linus Torvalds
2019-02-22 22:51 ` Alexei Starovoitov
2019-02-22 23:11 ` Jann Horn
2019-02-22 23:16 ` David Miller
2019-02-22 23:16 ` Linus Torvalds
2019-02-22 23:56 ` Alexei Starovoitov
2019-02-23 0:08 ` Linus Torvalds
2019-02-23 2:28 ` Alexei Starovoitov
2019-02-23 2:32 ` Linus Torvalds
2019-02-23 3:02 ` Steven Rostedt
2019-02-23 4:51 ` Masami Hiramatsu
2019-02-26 3:57 ` Christoph Hellwig
2019-02-26 15:24 ` Joel Fernandes
2019-02-28 12:29 ` Masami Hiramatsu
2019-02-28 15:18 ` Joel Fernandes
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