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

[Mathieu Desnoyers]

Hi Arnd, Russell, Linus,

Can we ensure the arm32 kprobes fix I submitted gets upstream before 5.0 final ?
It takes care of an illegal instruction issue with optimized kprobes on arm32.

Here is the current state of default kprobes configuration on arm32:
using them will trigger illegal instruction OOPS on v5.0-rc7, 4.19.24,
v4.14.102.

My fix is in "accepted" state in the arm patch tracking system:

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

Should I send it directly to Linus as well ?

Thanks,

Mathieu

----- On Feb 18, 2019, at 9:55 AM, Mathieu Desnoyers mathieu.desnoyers@xxxxxxxxxxxx wrote:

> ----- On Feb 18, 2019, at 7:26 AM, Greg Kroah-Hartman gregkh@xxxxxxxxxxxxxxxxxxx
> 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@xxxxxxxxxxxx> wrote:
>>> 
>>> > On Mon, Feb 4, 2019 at 7:15 PM Mathieu Desnoyers
>>> > <mathieu.desnoyers@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
>>> > > 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

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