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

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Date:   Fri, 7 Dec 2018 18:42:55 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Oleg Nesterov <oleg@...hat.com>,
        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 10:12:49PM +1100, Michael Ellerman wrote:
> "Dmitry V. Levin" <ldv@...linux.org> writes:
> > On Mon, Dec 03, 2018 at 06:18:23AM +0300, Dmitry V. Levin wrote:
> >> From: Elvira Khabirova <lineprinter@...linux.org>
> >> 
> >> Arch code should use tracehook_*() helpers, as documented
> >> in include/linux/tracehook.h,
> >> ptrace_report_syscall() is not expected to be used outside that file.
> >> 
> >> Co-authored-by: Dmitry V. Levin <ldv@...linux.org>
> >> Fixes: 5521eb4bca2d ("powerpc/ptrace: Add support for PTRACE_SYSEMU")
> >> Signed-off-by: Elvira Khabirova <lineprinter@...linux.org>
> >> Signed-off-by: Dmitry V. Levin <ldv@...linux.org>
> >> ---
> >> v4: rewritten to call tracehook_report_syscall_entry() once, compile-tested
> >> v3: add a descriptive comment
> >> v2: explicitly ignore tracehook_report_syscall_entry() return code
> >> 
> >>  arch/powerpc/kernel/ptrace.c | 54 +++++++++++++++++++++++-------------
> >>  1 file changed, 35 insertions(+), 19 deletions(-)
> >
> > 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.

> I wrote more or less the same patch, although I used a temporary bool.
> 
> > However, the bug blocks PTRACE_GET_SYSCALL_INFO, so please fix it.
> 
> Sorry, didn't realise it was blocking you.

We are changing ptrace_report_syscall signature to implement
PTRACE_GET_SYSCALL_INFO, and this is the only place in the kernel besides
tracehook_report_syscall_*() that invokes ptrace_report_syscall() directly.

> > I'm going to use
> > 	if (tracehook_report_syscall_entry(regs))
> > 		return -1;
> > 	return -1;
> > in the series until you have a better fix.
> 
> Yeah that's fine by me. I could send that to Linus for 4.20 if you want
> me to, otherwise I'm fine for you to carry it in your series.

Yes, please.  I'll send a v5 shortly.


-- 
ldv

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