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

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Date:   Wed, 13 Mar 2019 01:03:18 +0000
From:   "Haibo Xu (Arm Technology China)" <Haibo.Xu@....com>
To:     Sudeep Holla <Sudeep.Holla@....com>,
        Andy Lutomirski <luto@...nel.org>
CC:     "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 2019/3/12 20:09, Sudeep Holla wrote:
> 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
>

Since ptrace() system call do have so many request type, I'm not sure whether the
test cases have covered all of that. But here we'd better make sure the PTRACE_SYSEMU
and PTRACE_SYSEMU_SINGLESTEP requests are work correctly. May be you can verify them with
tests from Bin Lu(bin.lu@....com).

Regards,
Haibo
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