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

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

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?

> 
> Thanks,
> 
> Mathieu
> 
> ----- On Feb 18, 2019, at 9:55 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
> 
> > ----- On Feb 18, 2019, at 7:26 AM, Greg Kroah-Hartman gregkh@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@chromium.org> wrote:
> >>> 
> >>> > On Mon, Feb 4, 2019 at 7:15 PM Mathieu Desnoyers
> >>> > <mathieu.desnoyers@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@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
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
> 

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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