From: Daniel Borkmann <daniel@iogearbox.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>,
the arch/x86 maintainers <x86@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-parisc@vger.kernel.org,
linux-um <linux-um@lists.infradead.org>,
Netdev <netdev@vger.kernel.org>,
bpf@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
bgregg@netflix.com
Subject: Re: [PATCH 11/18] maccess: remove strncpy_from_unsafe
Date: Thu, 14 May 2020 01:24:18 +0200 [thread overview]
Message-ID: <2a03633b-419d-643f-b787-ca1520e2229b@iogearbox.net> (raw)
In-Reply-To: <CAHk-=wiivWJ70PotzCK-j7K4Y612NJBA2d+iN6Rz-bfMxCpwjQ@mail.gmail.com>
On 5/14/20 1:03 AM, Linus Torvalds wrote:
> On Wed, May 13, 2020 at 3:36 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>>
>> It's used for both.
>
> Daniel, BPF real;ly needs to make up its mind about that.
>
> You *cannot* use ti for both.
>
> Yes, it happens to work on x86 and some other architectures.
>
> But on other architectures, the exact same pointer value can be a
> kernel pointer or a user pointer.
Right, it has the same issue as with the old probe helper. I was merely stating that
there are existing users (on x86) out there that use it this way, even though broken
generally.
>> Given this is enabled on pretty much all program types, my
>> assumption would be that usage is still more often on kernel memory than user one.
>
> You need to pick one.
>
> If you know it is a user pointer, use strncpy_from_user() (possibly
> with disable_pagefault() aka strncpy_from_user_nofault()).
>
> And if you know it is a kernel pointer, use strncpy_from_unsafe() (aka
> strncpy_from_kernel_nofault()).
>
> You really can't pick the "randomly one or the other guess what I mean " option.
My preference would be to have %s, %sK, %sU for bpf_trace_printk() where the latter two
result in an explicit strncpy_from_kernel_nofault() or strncpy_from_user_nofault()
choice while the %s is converted as per your suggestion and it would still allow for a
grace period to convert existing users to the new variants, similar with what we did on
the bpf_probe_read_kernel() and bpf_probe_read_user() helpers to get this sorted out.
Thanks,
Daniel
next prev parent reply other threads:[~2020-05-13 23:24 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 16:00 clean up and streamline probe_kernel_* and friends v2 Christoph Hellwig
2020-05-13 16:00 ` [PATCH 01/18] maccess: unexport probe_kernel_write and probe_user_write Christoph Hellwig
2020-05-13 16:00 ` [PATCH 02/18] maccess: remove various unused weak aliases Christoph Hellwig
2020-05-13 16:00 ` [PATCH 03/18] maccess: remove duplicate kerneldoc comments Christoph Hellwig
2020-05-13 16:00 ` [PATCH 04/18] maccess: clarify " Christoph Hellwig
2020-05-13 16:00 ` [PATCH 05/18] maccess: update the top of file comment Christoph Hellwig
2020-05-13 16:00 ` [PATCH 06/18] maccess: rename strncpy_from_unsafe_user to strncpy_from_user_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 07/18] maccess: rename strncpy_from_unsafe_strict to strncpy_from_kernel_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 08/18] maccess: rename strnlen_unsafe_user to strnlen_user_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 09/18] maccess: remove probe_read_common and probe_write_common Christoph Hellwig
2020-05-13 16:00 ` [PATCH 10/18] maccess: unify the probe kernel arch hooks Christoph Hellwig
2020-05-14 1:13 ` Masami Hiramatsu
2020-05-19 5:46 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 11/18] maccess: remove strncpy_from_unsafe Christoph Hellwig
2020-05-13 19:11 ` Linus Torvalds
2020-05-13 19:28 ` Christoph Hellwig
2020-05-13 22:36 ` Daniel Borkmann
2020-05-13 23:03 ` Linus Torvalds
2020-05-13 23:24 ` Daniel Borkmann [this message]
2020-05-13 23:20 ` Masami Hiramatsu
2020-05-13 23:59 ` Linus Torvalds
2020-05-14 1:00 ` Masami Hiramatsu
2020-05-14 2:43 ` Linus Torvalds
2020-05-14 9:44 ` Masami Hiramatsu
2020-05-14 10:27 ` Daniel Borkmann
2020-05-13 23:28 ` Al Viro
2020-05-13 23:58 ` Daniel Borkmann
2020-05-14 10:01 ` David Laight
2020-05-14 10:21 ` Daniel Borkmann
2020-05-13 16:00 ` [PATCH 12/18] maccess: always use strict semantics for probe_kernel_read Christoph Hellwig
2020-05-13 16:00 ` [PATCH 13/18] maccess: move user access routines together Christoph Hellwig
2020-05-13 16:00 ` [PATCH 14/18] maccess: allow architectures to provide kernel probing directly Christoph Hellwig
2020-05-13 19:36 ` Linus Torvalds
2020-05-13 19:40 ` Christoph Hellwig
2020-05-13 19:48 ` Linus Torvalds
2020-05-13 19:54 ` Christoph Hellwig
2020-05-16 3:42 ` Masami Hiramatsu
2020-05-18 15:09 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 15/18] x86: use non-set_fs based maccess routines Christoph Hellwig
2020-05-13 16:00 ` [PATCH 16/18] maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 17/18] maccess: rename probe_user_{read,write} to copy_{from,to}_user_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 18/18] maccess: rename probe_kernel_address to get_kernel_nofault Christoph Hellwig
2020-05-13 19:37 ` clean up and streamline probe_kernel_* and friends v2 Linus Torvalds
2020-05-13 23:04 ` Daniel Borkmann
2020-05-13 23:20 ` Linus Torvalds
2020-05-19 5:50 ` Christoph Hellwig
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