From: Oleg Nesterov <oleg@redhat.com>
To: "Dmitry V. Levin" <ldv@altlinux.org>
Cc: Eugene Syromyatnikov <esyr@redhat.com>,
linux-kernel@vger.kernel.org,
Elvira Khabirova <lineprinter@altlinux.org>,
Paul Mackerras <paulus@samba.org>,
Andy Lutomirski <luto@kernel.org>,
Breno Leitao <leitao@debian.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v6] powerpc/ptrace: replace ptrace_report_syscall() with a tracehook call
Date: Mon, 10 Dec 2018 14:28:07 +0100 [thread overview]
Message-ID: <20181210132806.GA4177@redhat.com> (raw)
In-Reply-To: <20181207185226.GB31278@altlinux.org>
On 12/07, Dmitry V. Levin wrote:
>
> Please make either v5 or v6 edition of this fix, or any similar fix,
> into v4.20.
IIUC, v5 above means
[PATCH v5 23/25] powerpc/ptrace: replace ptrace_report_syscall() with a tracehook call
you sent in another series...
> long do_syscall_trace_enter(struct pt_regs *regs)
> {
> + struct thread_info *ti;
> + u32 cached_flags;
> +
> user_exit();
>
> - if (test_thread_flag(TIF_SYSCALL_EMU)) {
> - ptrace_report_syscall(regs);
> - /*
> - * Returning -1 will skip the syscall execution. We want to
> - * avoid clobbering any register also, thus, not 'gotoing'
> - * skip label.
> - */
> - return -1;
> - }
> + ti = current_thread_info();
> + cached_flags = READ_ONCE(ti->flags) &
> + (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE |
> + _TIF_SYSCALL_TRACEPOINT);
>
> - /*
> - * The tracer may decide to abort the syscall, if so tracehook
> - * will return !0. Note that the tracer may also just change
> - * regs->gpr[0] to an invalid syscall number, that is handled
> - * below on the exit path.
> - */
> - if (test_thread_flag(TIF_SYSCALL_TRACE) &&
> - tracehook_report_syscall_entry(regs))
> - goto skip;
> + if (cached_flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
> + int rc = tracehook_report_syscall_entry(regs);
> +
> + if (unlikely(cached_flags & _TIF_SYSCALL_EMU)) {
> + /*
> + * A nonzero return code from
> + * tracehook_report_syscall_entry() tells us
> + * to prevent the syscall execution, but
> + * we are not going to execute it anyway.
> + *
> + * Returning -1 will skip the syscall execution.
> + * We want to avoid clobbering any register also,
> + * thus, not 'gotoing' skip label.
> + */
> + return -1;
> + }
> +
> + if (rc) {
> + /*
> + * The tracer decided to abort the syscall.
> + * Note that the tracer may also just change
> + * regs->gpr[0] to an invalid syscall number,
> + * that is handled below on the exit path.
> + */
> + goto skip;
> + }
> + }
>
> /* Run seccomp after ptrace; allow it to set gpr[3]. */
> if (do_seccomp(regs))
> @@ -3293,7 +3309,7 @@ long do_syscall_trace_enter(struct pt_regs *regs)
> if (regs->gpr[0] >= NR_syscalls)
> goto skip;
>
> - if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
> + if (unlikely(cached_flags & _TIF_SYSCALL_TRACEPOINT))
I will leave this to maintainers, but to me this change looks good and imo it
also cleanups the code.
However I am not sure cached_flags should include _TIF_SYSCALL_TRACEPOINT. If
nothing else, the caller can sleep in ptrace_stop() unpredictably long and
TIF_SYSCALL_TRACEPOINT can be set/cleared meanwhile.
Oleg.
next prev parent reply other threads:[~2018-12-10 13:30 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-16 11:17 [PATCH v2] powerpc/ptrace: replace ptrace_report_syscall() with a tracehook call Elvira Khabirova
2018-11-16 12:42 ` Michael Ellerman
2018-11-19 21:01 ` [PATCH v3] " Dmitry V. Levin
2018-11-21 21:17 ` Michael Ellerman
2018-12-03 3:18 ` [PATCH v4] " Dmitry V. Levin
2018-12-07 1:19 ` Dmitry V. Levin
2018-12-07 11:12 ` Michael Ellerman
2018-12-07 15:42 ` Dmitry V. Levin
2018-12-07 15:56 ` [PATCH v5] " Dmitry V. Levin
2018-12-07 18:52 ` [PATCH v6] " Dmitry V. Levin
2018-12-10 13:28 ` Oleg Nesterov [this message]
2018-12-10 13:36 ` Dmitry V. Levin
2018-12-16 17:28 ` [PATCH] powerpc/ptrace: cleanup do_syscall_trace_enter Dmitry V. Levin
2018-12-17 11:20 ` Michael Ellerman
2018-12-17 11:23 ` Dmitry V. Levin
2018-12-17 11:27 ` Oleg Nesterov
2018-12-22 9:54 ` Michael Ellerman
2018-12-11 13:45 ` [v5] powerpc/ptrace: replace ptrace_report_syscall() with a tracehook call Michael Ellerman
2018-12-07 16:34 ` [PATCH v4] " Oleg Nesterov
2018-12-07 18:42 ` Dmitry V. Levin
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