[PATCH RFC POC 09/50] m68k: commit fds on syscall exit

[Christian Brauner]

Add TIF_FD_SLOTS and test it on the untraced return from a system
call in all three entry paths. A task that reserved descriptors calls
syscall_trace_leave(), which commits them before the ptrace exit stop.
The traced paths already end up there.

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 arch/m68k/68000/entry.S             | 10 ++++++++++
 arch/m68k/coldfire/entry.S          | 12 ++++++++++++
 arch/m68k/include/asm/thread_info.h |  2 ++
 arch/m68k/kernel/entry.S            |  2 ++
 arch/m68k/kernel/ptrace.c           |  3 +++
 5 files changed, 29 insertions(+)

diff --git a/arch/m68k/68000/entry.S b/arch/m68k/68000/entry.S
index c257cc415c47..479032af2f2f 100644
--- a/arch/m68k/68000/entry.S
+++ b/arch/m68k/68000/entry.S
@@ -89,6 +89,16 @@ ENTRY(system_call)
 	jbsr	%a0@
 	movel	%d0,%sp@(PT_OFF_D0)	/* save the return value*/
 
+	/* descriptors reserved by the syscall are committed in syscall_trace_leave */
+	getthreadinfo
+	btst	#(TIF_FD_SLOTS%8),%a2@(TINFO_FLAGS+(31-TIF_FD_SLOTS)/8)
+	jeq	ret_from_exception
+	subql	#4,%sp			/* dummy return address */
+	SAVE_SWITCH_STACK
+	jbsr	syscall_trace_leave
+	RESTORE_SWITCH_STACK
+	addql	#4,%sp
+
 ret_from_exception:
 	btst	#5,%sp@(PT_OFF_SR)	/* check if returning to kernel*/
 	jeq	Luser_return		/* if so, skip resched, signals*/
diff --git a/arch/m68k/coldfire/entry.S b/arch/m68k/coldfire/entry.S
index 4ea08336e2fb..43e47d4c0018 100644
--- a/arch/m68k/coldfire/entry.S
+++ b/arch/m68k/coldfire/entry.S
@@ -78,6 +78,18 @@ ENTRY(system_call)
 	movel	%d3,%a0
 	jbsr	%a0@
 	movel	%d0,%sp@(PT_OFF_D0)	/* save the return value */
+
+	/* descriptors reserved by the syscall are committed in syscall_trace_leave */
+	movel	%sp,%d2			/* get thread_info pointer */
+	andl	#-THREAD_SIZE,%d2	/* at start of kernel stack */
+	movel	%d2,%a0
+	btst	#(TIF_FD_SLOTS%8),%a0@(TINFO_FLAGS+(31-TIF_FD_SLOTS)/8)
+	jeq	ret_from_exception
+	subql	#4,%sp			/* dummy return address */
+	SAVE_SWITCH_STACK
+	jbsr	syscall_trace_leave
+	RESTORE_SWITCH_STACK
+	addql	#4,%sp
 	jra	ret_from_exception
 1:
 	movel	#-ENOSYS,%d2		/* strace needs -ENOSYS in PT_OFF_D0 */
diff --git a/arch/m68k/include/asm/thread_info.h b/arch/m68k/include/asm/thread_info.h
index 5cb3ace55622..861b6f523bda 100644
--- a/arch/m68k/include/asm/thread_info.h
+++ b/arch/m68k/include/asm/thread_info.h
@@ -62,6 +62,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_NOTIFY_RESUME	5	/* callback before returning to user */
 #define TIF_SIGPENDING		6	/* signal pending */
 #define TIF_NEED_RESCHED	7	/* rescheduling necessary */
+#define TIF_FD_SLOTS		12	/* syscall prepared descriptors */
 #define TIF_SECCOMP		13	/* seccomp syscall filtering active */
 #define TIF_DELAYED_TRACE	14	/* single step a syscall */
 #define TIF_SYSCALL_TRACE	15	/* syscall trace active */
@@ -71,6 +72,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_FD_SLOTS		(1 << TIF_FD_SLOTS)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_DELAYED_TRACE	(1 << TIF_DELAYED_TRACE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index 338b474910f7..9e4471f68165 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -229,6 +229,8 @@ ret_from_syscall:
 syscall_exit_work:
 	btst	#5,%sp@(PT_OFF_SR)	| check if returning to kernel
 	bnes	1b			| if so, skip resched, signals
+	btst	#4,%a1@(TINFO_FLAGS+2)	| TIF_FD_SLOTS: commit descriptors
+	jne	do_trace_exit
 	lslw	#1,%d0
 	jcs	do_trace_exit
 	jmi	do_delayed_trace
diff --git a/arch/m68k/kernel/ptrace.c b/arch/m68k/kernel/ptrace.c
index 4575f6487a9a..07103e6ddeb0 100644
--- a/arch/m68k/kernel/ptrace.c
+++ b/arch/m68k/kernel/ptrace.c
@@ -11,6 +11,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/file.h>
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
 #include <linux/mm.h>
@@ -289,6 +290,8 @@ asmlinkage int syscall_trace_enter(void)
 
 asmlinkage void syscall_trace_leave(void)
 {
+	if (test_thread_flag(TIF_FD_SLOTS))
+		fd_slots_commit(task_pt_regs(current));
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		ptrace_report_syscall_exit(task_pt_regs(current), 0);
 }

-- 
2.53.0