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

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Date:   Thu, 21 Feb 2019 19:17:11 -0500 (EST)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     "Russell King, ARM Linux" <linux@...linux.org.uk>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        William Cohen <wcohen@...hat.com>,
        stable <stable@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        lttng <lttng@...iableembeddedsystems.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: BUG: optimized kprobes illegal instructions in v4.19 stable
 kernels

----- On Feb 21, 2019, at 7:10 PM, Russell King, ARM Linux linux@...linux.org.uk wrote:

> On Thu, Feb 21, 2019 at 03:02:57PM -0500, Mathieu Desnoyers wrote:
>> 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 ?
> 
> Accepted means it's in my tree pending to be sent to Linus.  It should
> now be in mainline.  Have you checked?

Hrm, why did I not see it earlier today... it's embarrassing.

It's there indeed, all is good!

Greg, you should be able to pick it into the stable kernels now.

Thanks,

Mathieu


> 
>> 
>> Thanks,
>> 
>> Mathieu
>> 
>> ----- On Feb 18, 2019, at 9:55 AM, Mathieu Desnoyers
>> mathieu.desnoyers@...icios.com wrote:
>> 
>> > ----- On Feb 18, 2019, at 7:26 AM, Greg Kroah-Hartman 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...
>> > 
>> > 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
>> 
> 
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
> According to speedtest.net: 11.9Mbps down 500kbps up

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