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Date:   Fri, 7 Dec 2018 18:56:05 +0300
From:   "Dmitry V. Levin" <ldv@altlinux.org>
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Elvira Khabirova <lineprinter@altlinux.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Breno Leitao <leitao@debian.org>,
        Andy Lutomirski <luto@kernel.org>,
        Eugene Syromyatnikov <esyr@redhat.com>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: [PATCH v5] powerpc/ptrace: replace ptrace_report_syscall() with a
 tracehook call
Message-ID: <20181207155605.GB28964@altlinux.org>
References: <20181116121701.14359da0@akathisia>
 <87ftw12nyn.fsf@concordia.ellerman.id.au>
 <20181119210139.GA8360@altlinux.org>
 <87efbe166y.fsf@concordia.ellerman.id.au>
 <20181203031823.GE11573@altlinux.org>
 <20181207011946.GA18558@altlinux.org>
 <87y391k2tq.fsf@concordia.ellerman.id.au>
 <20181207154255.GA28964@altlinux.org>
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From: Elvira Khabirova <lineprinter@altlinux.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.

The patch does not look very nice, but at least it is correct
and opens the way for PTRACE_GET_SYSCALL_INFO API.

Co-authored-by: Dmitry V. Levin <ldv@altlinux.org>
Fixes: 5521eb4bca2d ("powerpc/ptrace: Add support for PTRACE_SYSEMU")
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Eugene Syromyatnikov <esyr@redhat.com>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Elvira Khabirova <lineprinter@altlinux.org>
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
---
v5: reverted to a simple approach, compile- and run-tested
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 | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index afb819f4ca68..714c3480c52d 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -3266,12 +3266,17 @@ long do_syscall_trace_enter(struct pt_regs *regs)
 	user_exit();
 
 	if (test_thread_flag(TIF_SYSCALL_EMU)) {
-		ptrace_report_syscall(regs);
 		/*
+		 * 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.
 		 */
+		if (tracehook_report_syscall_entry(regs))
+			;
 		return -1;
 	}
 
-- 
ldv