From: Sudeep Holla <sudeep.holla@arm.com>
To: "Haibo Xu (Arm Technology China)" <Haibo.Xu@arm.com>
Cc: "x86@kernel.org" <x86@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
Catalin Marinas <Catalin.Marinas@arm.com>,
Will Deacon <Will.Deacon@arm.com>,
Oleg Nesterov <oleg@redhat.com>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Richard Weinberger <richard@nod.at>,
"jdike@addtoit.com" <jdike@addtoit.com>,
Steve Capper <Steve.Capper@arm.com>,
"Bin Lu (Arm Technology China)" <Bin.Lu@arm.com>,
Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 3/6] x86: clean up _TIF_SYSCALL_EMU handling using ptrace_syscall_enter hook
Date: Tue, 12 Mar 2019 12:05:29 +0000 [thread overview]
Message-ID: <20190312120529.GA13825@e107155-lin> (raw)
In-Reply-To: <65b00ea1-f784-4fb4-2a98-49fa44d9fa8f@arm.com>
On Tue, Mar 12, 2019 at 01:34:44AM +0000, Haibo Xu (Arm Technology China) wrote:
> On 2019/3/12 2:34, Sudeep Holla wrote:
> > (I thought I had sent this email, last Tuesday itself, but saw this in my
> > draft today, something went wrong, sorry for the delay)
> >
> > On Tue, Mar 05, 2019 at 02:14:47AM +0000, Haibo Xu (Arm Technology China) wrote:
> >> On 2019/3/4 18:12, Sudeep Holla wrote:
> >>> On Mon, Mar 04, 2019 at 08:25:28AM +0000, Haibo Xu (Arm Technology China) wrote:
> >>>> On 2019/3/1 2:32, Sudeep Holla wrote:
> >>>>> Now that we have a new hook ptrace_syscall_enter that can be called from
> >>>>> syscall entry code and it handles PTRACE_SYSEMU in generic code, we
> >>>>> can do some cleanup using the same in syscall_trace_enter.
> >>>>>
> >>>>> Further the extra logic to find single stepping PTRACE_SYSEMU_SINGLESTEP
> >>>>> in syscall_slow_exit_work seems unnecessary. Let's remove the same.
> >>>>
> >>>> I think we should not change the logic here. Is so, it will double the report of syscall
> >>>> when PTRACE_SYSEMU_SINGLESTEP is enabled.
> >>>>
> >>>
> >>> I don't think that should happen, but I may be missing something.
> >>> Can you explain how ?
> >>>
> >>
> >> When PTRACE_SYSEMU_SINGLESTEP is enabled, both the _TIF_SYSCALL_EMU and
> >> _TIF_SINGLESTEP flags are set, but 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.
> >>
> > Sorry, but I still not get it, we have:
> >
> > step = ((flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) == _TIF_SINGLESTEP);
> >
> > For me, this is same as:
> > step = ((flags & _TIF_SINGLESTEP) == _TIF_SINGLESTEP)
> > or
> > if (flags & _TIF_SINGLESTEP)
> > step = true;
> >
>
> I don't think so! As I mentioned in the last email loop, when
> PTRACE_SYSEMU_SINGLESTE is enabled, both the _TIF_SYSCALL_EMU and
> _TIF_SINGLESTEP flags are set, in which case the step should be "false" for
> the old logic. But with the new logic, the step is "true".
>
Ah right, sorry I missed that.
> > So when PTRACE_SYSEMU_SINGLESTEP, _TIF_SYSCALL_EMU and _TIF_SINGLESTEP
> > are set and step evaluates to true.
> >
> > So dropping _TIF_SYSCALL_EMU here should be fine. Am I still missing
> > something ?
> >
> > --
> > Regards,
> > Sudeep
> >
>
> 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).
>
Understood
> 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.
>
I did run selftests after Andy Lutomirski pointed out. Nothing got flagged,
I haven't looked at the tests themselves yet, but it clearly misses this
case.
--
Regards,
Sudeep
next prev parent reply other threads:[~2019-03-12 12:05 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-28 18:32 [PATCH 0/6] ptrace: consolidate PTRACE_SYSEMU handling and add support for arm64 Sudeep Holla
2019-02-28 18:32 ` [PATCH 1/6] ptrace: move clearing of TIF_SYSCALL_EMU flag to core Sudeep Holla
2019-02-28 18:32 ` [PATCH 2/6] ptrace: introduce ptrace_syscall_enter to consolidate PTRACE_SYSEMU handling Sudeep Holla
2019-03-04 8:03 ` Haibo Xu (Arm Technology China)
2019-03-04 10:46 ` Sudeep Holla
2019-03-04 12:23 ` Segher Boessenkool
2019-03-04 12:27 ` Sudeep Holla
2019-02-28 18:32 ` [PATCH 3/6] x86: clean up _TIF_SYSCALL_EMU handling using ptrace_syscall_enter hook Sudeep Holla
2019-03-03 1:11 ` Andy Lutomirski
2019-03-04 10:07 ` Sudeep Holla
2019-03-04 8:25 ` Haibo Xu (Arm Technology China)
2019-03-04 10:12 ` Sudeep Holla
2019-03-05 2:14 ` Haibo Xu (Arm Technology China)
2019-03-11 18:34 ` Sudeep Holla
2019-03-12 1:34 ` Haibo Xu (Arm Technology China)
2019-03-12 3:04 ` Andy Lutomirski
2019-03-12 12:09 ` Sudeep Holla
2019-03-13 1:03 ` Haibo Xu (Arm Technology China)
2019-03-14 10:51 ` Sudeep Holla
2019-03-15 5:48 ` Haibo Xu (Arm Technology China)
2019-03-12 12:05 ` Sudeep Holla [this message]
2019-02-28 18:32 ` [PATCH 4/6] powerpc: use common ptrace_syscall_enter hook to handle _TIF_SYSCALL_EMU Sudeep Holla
2019-03-04 9:36 ` Haibo Xu (Arm Technology China)
2019-03-04 10:42 ` Sudeep Holla
2019-02-28 18:32 ` [PATCH 5/6] arm64: add PTRACE_SYSEMU{,SINGLESTEP} definations to uapi headers Sudeep Holla
2019-02-28 18:32 ` [PATCH 6/6] arm64: ptrace: add support for syscall emulation Sudeep Holla
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190312120529.GA13825@e107155-lin \
--to=sudeep.holla@arm.com \
--cc=Bin.Lu@arm.com \
--cc=Catalin.Marinas@arm.com \
--cc=Haibo.Xu@arm.com \
--cc=Steve.Capper@arm.com \
--cc=Will.Deacon@arm.com \
--cc=bp@alien8.de \
--cc=jdike@addtoit.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=mpe@ellerman.id.au \
--cc=oleg@redhat.com \
--cc=paulus@samba.org \
--cc=richard@nod.at \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).