linux-kernel - Re: [PATCH v4] powerpc/ptrace: replace ptrace_report

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Message-ID: <20181207184246.GA31278@altlinux.org>
Date:   Fri, 7 Dec 2018 21:42:46 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Breno Leitao <leitao@...ian.org>,
        Andy Lutomirski <luto@...nel.org>,
        Eugene Syromyatnikov <esyr@...hat.com>,
        Elvira Khabirova <lineprinter@...linux.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] powerpc/ptrace: replace ptrace_report_syscall() with
 a tracehook call

On Fri, Dec 07, 2018 at 05:34:10PM +0100, Oleg Nesterov wrote:
> On 12/07, Dmitry V. Levin wrote:
> > On Fri, Dec 07, 2018 at 10:12:49PM +1100, Michael Ellerman wrote:
> >
> > > > Sorry, this patch does not work, please ignore it.
> > >
> > > Hmm OK. Why exactly?
> >
> > Unfortunately, I have no idea why it doesn't work.
> > All I can say is it breaks strace because the kernel no longer sends
> > syscall entry stops.
> 
> May be because TIF_SYSCALL_EMU/etc is a bit number, not a mask? IOW, rather
> than
> 
> 	whatever & TIF_XXX
> 
> you should do
> 
> 	whatever & _TIF_XXX
> 
> intstead?

Thanks Oleg, this was exactly the reason why it didn't work.
That kind of things happens when you let userspace people hack you kernel. :)


-- 
ldv

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