Re: [PATCH 0/2] [GIT PULL] tracing: Two more fixes

From: Steven Rostedt
Date: Fri Feb 15 2019 - 12:22:14 EST

On Fri, 15 Feb 2019 09:08:38 -0800
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Fri, Feb 15, 2019 at 6:21 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> >
> > - Have kprobes not use copy_from_user to access kernel addresses
> > as this is now considered a security issue.
> No, you people are confused.
> The problem isn't that it's using a user access function on kernel memory.
> The problem is that it's using a user access function on a complete
> garbage pointer that happens to not even be a valid pointer at all.
> You get a GP fault because the code tries to access an address at
> 0x2e646c2f6374652f.
> That's not a valid pointer on x86-64. Nothing to do with user or
> kernel, everything to do with "it's garbage".
> Switching over to probe_mem_read() just means that even non-canonical
> address faults are ignored. But it has absolutely nothing to do with
> "kernel addresses" or any security issues.
> So the patch looks like it might be ok, but the explanations for it
> are garbage and only confuse the issue.
> Please fix the explanations, I don't want to have actively wrong
> commit messages for when people start looking at things like this.

OK, I'll update the change log. Yeah, the bug is that we are reading
possibly bad kernel memory, which is what kprobes do.

Will update.

-- Steve