[lttng-dev] BUG: optimized kprobes illegal instructions in v4.19 stable kernels

[Mathieu Desnoyers]

----- On Feb 18, 2019, at 7:26 AM, Greg Kroah-Hartman gregkh at linuxfoundation.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 at chromium.org> wrote:
>> 
>> > On Mon, Feb 4, 2019 at 7:15 PM Mathieu Desnoyers
>> > <mathieu.desnoyers at efficios.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 at chromium.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...

It seems to still be in the arm patch tracking system:

https://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=8834/1

If I understand its status correctly, it is applied to the arm tree, but
perhaps it has not been pulled by Linus yet ? The code is still broken
in Linus' master.

It would be important to get this arm kprobes fix upstream before 5.0
final.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com