linux-kernel - Re: BUG: optimized kprobes illegal instructions in v4.19 stable kernels

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Date:   Mon, 18 Feb 2019 23:11:42 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        William Cohen <wcohen@...hat.com>,
        "# 3.4.x" <stable@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        lttng@...iableembeddedsystems.com,
        lttng-dev <lttng-dev@...ts.lttng.org>
Subject: Re: BUG: optimized kprobes illegal instructions in v4.19 stable
 kernels

On Mon, 18 Feb 2019 13:26:31 +0100
Greg KH <gregkh@...uxfoundation.org> wrote:

> On Wed, Feb 06, 2019 at 01:41:15PM +0900, Masami Hiramatsu wrote:
> > On Tue, 5 Feb 2019 15:06:10 +0000
> > Kees Cook <keescook@...omium.org> wrote:
> > 
> > > On Mon, Feb 4, 2019 at 7:15 PM Mathieu Desnoyers
> > > <mathieu.desnoyers@...icios.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > I notice this commit as a possible culprit of the illegal instructions my lttng
> > > > users are noticing on arm32 when using kprobes on a v4.19.13 Linux kernel
> > > > in a Yocto environment [1]. They were able to reproduce the issue with perf
> > > > as well.
> > > >
> > > > commit e46daee53bb50bde38805f1823a182979724c229
> > > > Author: Kees Cook <keescook@...omium.org>
> > > > Date:   Tue Oct 30 22:12:56 2018 +0100
> > > >
> > > >     ARM: 8806/1: kprobes: Fix false positive with FORTIFY_SOURCE
> > > >
> > > > I *think* the intent there was to do
> > > >
> > > > -       memcpy(code, &optprobe_template_entry,
> > > > +       memcpy(code, (unsigned long *)&optprobe_template_entry,
> > > >
> > > > But if you look at the commit, the "&" seems to have been stripped away,
> > > > which happens to change the behavior significantly.
> > > 
> > > Yeah, this was a typo on my part. :(
> > 
> > Ah, I thought it had been fixed as same as x86.
> > On x86, all optprobe_template_* are defined as kprobe_opcode_t [],
> > but on arm, it still be kprobe_opcode_t.
> > 
> > Hmm, but I think we should use kprobe_opcode_t [] or char[] as asm/sections.h does.
> > OK, I'll prepare for the change.
> 
> Did this ever get fixed in Linus's tree?  If so, what is the git commit
> id, I can't seem to find anything...

I would like to wait for picking up Mathieu's patch which I acked, since
it is simpler and minimum fix. 

https://patchwork.kernel.org/patch/10797511/

After this, I will send my update to change the optprobe_template_*
definitions which will involves wider code, and need to be tested.

Thank you,


-- 
Masami Hiramatsu <mhiramat@...nel.org>