linux-kernel - Re: [PATCH 3/6] x86: clean up _TIF_SYSCALL_EMU handling using ptrace_syscall

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Date:   Tue, 12 Mar 2019 12:09:44 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "Haibo Xu (Arm Technology China)" <Haibo.Xu@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Will Deacon <Will.Deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Richard Weinberger <richard@....at>,
        "jdike@...toit.com" <jdike@...toit.com>,
        Steve Capper <Steve.Capper@....com>,
        "Bin Lu (Arm Technology China)" <Bin.Lu@....com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 3/6] x86: clean up _TIF_SYSCALL_EMU handling using
 ptrace_syscall_enter hook

On Mon, Mar 11, 2019 at 08:04:39PM -0700, Andy Lutomirski wrote:
> On Mon, Mar 11, 2019 at 6:35 PM Haibo Xu (Arm Technology China)
> <Haibo.Xu@....com> wrote:
> >

[...]

> > For the PTRACE_SYSEMU_SINGLESTEP request, ptrace only need to report(send
> > SIGTRAP) at the entry of a system call, no need to report at the exit of a
> > system call.That's why the old logic-{step = ((flags & (_TIF_SINGLESTEP |
> > _TIF_SYSCALL_EMU)) == _TIF_SINGLESTEP)} here try to filter out the special
> > case(PTRACE_SYSEMU_SINGLESTEP).
> >
> > Another way to make sure the logic is fine, you can run some tests with
> > respect to both logic, and to check whether they have the same behavior.
>
> tools/testing/selftests/x86/ptrace_syscall.c has a test intended to
> exercise this.  Can one of you either confirm that it does exercise it
> and that it still passes or can you improve the test?
>
I did run the tests which didn't flag anything. I haven't looked at the
details of test implementation, but seem to miss this case. I will see
what can be improved(if it's possible). Also I think single_step_syscall
is the one I need to look for this particular one. Both single_step_syscall
ptrace_syscall reported no errors.

--
Regards,
Sudeep