[PATCH RFC v2] m68k/kernel - wire up syscall_trace_enter/leave for m68k

From: Michael Schmitz <schmitzmic@gmail.com>
To: glaubitz@physik.fu-berlin.de, geert@linux-m68k.org
Cc: linux-m68k@vger.kernel.org, schwab@linux-m68k.org,
	Michael Schmitz <schmitzmic@gmail.com>
Subject: [PATCH RFC v2] m68k/kernel - wire up syscall_trace_enter/leave for m68k
Date: Sun, 26 Jul 2020 13:28:50 +1200	[thread overview]
Message-ID: <1595726930-8969-1-git-send-email-schmitzmic@gmail.com> (raw)
In-Reply-To: <f0c9edc0-e596-c483-b9a6-f67778bd297c@physik.fu-berlin.de>

m68k (other than Coldfire) uses syscall_trace for both trace entry
and trace exit. Seccomp support requires separate entry points for
trace entry and exit which are already provided for Coldfire.

Replace syscall_trace by syscall_trace_enter and syscall_trace_leave
in preparation for seccomp support. Check return code of
syscall_trace_enter(), and skip syscall if nonzero. Return code
will be set to -EPERM in that case.

No regression seen in testing with strace on ARAnyM.

Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
---

Changes from v1:

- add return code check in do_trace_entry branch to enable syscall
  filtering (will return -EPERM)
- change to use testl for return code check (suggested by Andreas Schwab)
 
---
 arch/m68k/kernel/entry.S  |   11 ++++++++---
 arch/m68k/kernel/ptrace.c |   17 -----------------
 2 files changed, 8 insertions(+), 20 deletions(-)

diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index 9dd76fb..fbd2222 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -164,20 +164,25 @@ do_trace_entry:
 	movel	#-ENOSYS,%sp@(PT_OFF_D0)| needed for strace
 	subql	#4,%sp
 	SAVE_SWITCH_STACK
-	jbsr	syscall_trace
+	jbsr	syscall_trace_enter
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp
+	tstl	%d0
+	jne	denied
 	movel	%sp@(PT_OFF_ORIG_D0),%d0
 	cmpl	#NR_syscalls,%d0
 	jcs	syscall
 badsys:
 	movel	#-ENOSYS,%sp@(PT_OFF_D0)
 	jra	ret_from_syscall
+denied:
+	movel	#-EPERM,%sp@(PT_OFF_D0)
+	jra	ret_from_syscall
 
 do_trace_exit:
 	subql	#4,%sp
 	SAVE_SWITCH_STACK
-	jbsr	syscall_trace
+	jbsr	syscall_trace_leave
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp
 	jra	.Lret_from_exception
@@ -186,7 +191,7 @@ ENTRY(ret_from_signal)
 	movel	%curptr@(TASK_STACK),%a1
 	tstb	%a1@(TINFO_FLAGS+2)
 	jge	1f
-	jbsr	syscall_trace
+	jbsr	syscall_trace_leave
 1:	RESTORE_SWITCH_STACK
 	addql	#4,%sp
 /* on 68040 complete pending writebacks if any */
diff --git a/arch/m68k/kernel/ptrace.c b/arch/m68k/kernel/ptrace.c
index 748c63b..b747a86 100644
--- a/arch/m68k/kernel/ptrace.c
+++ b/arch/m68k/kernel/ptrace.c
@@ -272,22 +272,6 @@ long arch_ptrace(struct task_struct *child, long request,
 	return -EIO;
 }
 
-asmlinkage void syscall_trace(void)
-{
-	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
-				 ? 0x80 : 0));
-	/*
-	 * this isn't the same as continuing with a signal, but it will do
-	 * for normal use.  strace only continues with a signal if the
-	 * stopping signal is not SIGTRAP.  -brl
-	 */
-	if (current->exit_code) {
-		send_sig(current->exit_code, current, 1);
-		current->exit_code = 0;
-	}
-}
-
-#if defined(CONFIG_COLDFIRE) || !defined(CONFIG_MMU)
 asmlinkage int syscall_trace_enter(void)
 {
 	int ret = 0;
@@ -302,4 +286,3 @@ asmlinkage void syscall_trace_leave(void)
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		tracehook_report_syscall_exit(task_pt_regs(current), 0);
 }
-#endif /* CONFIG_COLDFIRE */
-- 
1.7.0.4

