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From: Steven Rostedt <rostedt@goodmis.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	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>,
	Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault
Date: Fri, 15 Feb 2019 21:08:01 -0500	[thread overview]
Message-ID: <20190215210801.7f8c94cf@gandalf.local.home> (raw)
In-Reply-To: <D1A39BE5-CAB2-42D1-B87B-2E21906FE5B1@amacapital.net>

On Fri, 15 Feb 2019 17:32:55 -0800
Andy Lutomirski <luto@amacapital.net> wrote:

> > I added you just because I wanted help getting the change log correct,
> > as that's what Linus was complaining about. I kept using "kernel
> > address" when the sample bug used for the patch was really a
> > non-canonical address (as Linus said, it's just garbage. Neither kernel
> > or user space). But I pointed out that this can also bug if the
> > address is canonical and in the kernel address space. The old code
> > didn't complain about non-canonical or kernel address faulting before
> > commit 9da3f2b7405, which only talks about kernel address space
> > faulting (which is why I only mentioned that in my messages).
> > 
> > Would changing all the mention of "kernel address" to "non user space"
> > be accurate?
> >   
> 
> I think “kernel address” is right. It’s illegal to access anything that isn’t known to be a valid kernel address while in KERNEL_DS.

But an non-canonical address is not a "kernel address", and that will
cause a bug too. This patch came about because it was changed that if
we do a uaccess on something other than a user space address and take a
fault (either because it was a non-canonical address, or a kernel
address), we BUG! Where before that one patch, it would just return a
fault.

> 
> The old __copy seems likely to have always been a bit bogus.
> 
> BTW, what is this probe_mem_read() thing?  Some minimal inspection suggests it’s a buggy reimplementation of probe_kernel_read().  Can you delete it and just use probe_kernel_read() directly?

Well, the issue is that we have trace_probe_tmpl.h in that same
directory, which does the work for kprobes and uprobes. The
trace_kprobes.c defines all the functions for handling kprobes, and
trace_uprobes.c does all the handling of uprobes, then they include
trace_probe_tmpl.h which does the bulk of the work.

In the uprobes case, we have:

static nokprobe_inline int
probe_mem_read(void *dest, void *src, size_t size)
{
	void __user *vaddr = (void __force __user *)src;

	return copy_from_user(dest, vaddr, size) ? -EFAULT : 0;
}

Because that is adding probes on userspace code.

-- Steve

  reply	other threads:[~2019-02-16  2:08 UTC|newest]

Thread overview: 85+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-15 17:47 [PATCH 0/2 v2] [GIT PULL (take two)] tracing: Two more fixes Steven Rostedt
2019-02-15 17:47 ` [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault Steven Rostedt
2019-02-15 17:55   ` Linus Torvalds
2019-02-15 22:15     ` Steven Rostedt
2019-02-15 23:49       ` Andy Lutomirski
2019-02-16  0:19         ` Steven Rostedt
2019-02-16  1:32           ` Andy Lutomirski
2019-02-16  2:08             ` Steven Rostedt [this message]
2019-02-16  2:14               ` Andy Lutomirski
2019-02-16  2:21                 ` Steven Rostedt
2019-02-18 17:58           ` Linus Torvalds
2019-02-18 18:23             ` Linus Torvalds
2019-02-19 16:18               ` Steven Rostedt
2019-02-19 18:43                 ` Linus Torvalds
2019-02-19 19:03                   ` Steven Rostedt
2019-02-20  8:10                     ` Masami Hiramatsu
2019-02-20 13:57                       ` Jann Horn
2019-02-20 14:47                         ` Steven Rostedt
2019-02-20 15:08                         ` Masami Hiramatsu
2019-02-20 14:49                       ` Steven Rostedt
2019-02-20 16:04                         ` Masami Hiramatsu
2019-02-20 16:42                           ` Steven Rostedt
2019-02-21  7:37                             ` Masami Hiramatsu
2019-02-22  8:27                         ` Masami Hiramatsu
2019-02-22  8:35                           ` Masami Hiramatsu
2019-02-22 17:43                             ` Linus Torvalds
2019-02-22 17:48                               ` Andy Lutomirski
2019-02-22 18:28                                 ` Linus Torvalds
2019-02-22 19:52                                   ` Andy Lutomirski
2019-02-22 19:27                               ` 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
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
2019-02-23  3:47                               ` Masami Hiramatsu
2019-02-24  0:44                                 ` Steven Rostedt
2019-02-24  4:38                                   ` Andy Lutomirski
2019-02-24 15:17                                     ` Masami Hiramatsu
2019-02-24 17:26                                       ` Linus Torvalds
2019-02-25  2:40                                         ` Masami Hiramatsu
2019-02-25  4:49                                           ` Andy Lutomirski
2019-02-25  8:09                                             ` Masami Hiramatsu
2019-02-25 16:40                                               ` Steven Rostedt
2019-02-26  1:35                                                 ` Masami Hiramatsu
2019-02-25  8:33                                         ` Peter Zijlstra
2019-02-25 14:52                                           ` Peter Zijlstra
2019-02-25 16:48                                     ` Kees Cook
2019-02-25 16:58                                       ` Andy Lutomirski
2019-02-25 17:07                                         ` Kees Cook
2019-02-21  7:52   ` Masami Hiramatsu
2019-02-21 14:36     ` Steven Rostedt
2019-02-21 15:58       ` Masami Hiramatsu
2019-02-21 16:16         ` Masami Hiramatsu
2019-02-21 16:32           ` Steven Rostedt
2019-02-23 14:48     ` Masami Hiramatsu
2019-02-15 17:47 ` [PATCH 2/2 v2] tracing: Fix number of entries in trace header Steven Rostedt

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