[PATCH RFC POC 05/50] ARM: commit fds on syscall exit

[Christian Brauner]

Add TIF_FD_SLOTS and test it where the syscall return path decides
between the syscall work and the plain work pending slow path. A task
that reserved descriptors goes through __sys_trace_return_nosave
where syscall_trace_exit() commits them before audit and the ptrace
exit stop. The traced path already ends up there.

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 arch/arm/include/asm/thread_info.h | 2 ++
 arch/arm/kernel/entry-common.S     | 2 ++
 arch/arm/kernel/ptrace.c           | 4 ++++
 3 files changed, 8 insertions(+)

diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 943ffcf069d2..5337449e8409 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -144,6 +144,7 @@ extern int vfp_restore_user_hwstate(struct user_vfp *,
 #define TIF_NOTIFY_RESUME	2	/* callback before returning to user */
 #define TIF_UPROBE		3	/* breakpointed or singlestepping */
 #define TIF_NOTIFY_SIGNAL	4	/* signal notifications exist */
+#define TIF_FD_SLOTS		5	/* syscall prepared descriptors, entry-common.S needs it below 16 */
 
 #define TIF_USING_IWMMXT	17
 #define TIF_MEMDIE		18	/* is terminating due to OOM killer */
@@ -163,6 +164,7 @@ extern int vfp_restore_user_hwstate(struct user_vfp *,
 #define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
+#define _TIF_FD_SLOTS		(1 << TIF_FD_SLOTS)
 #define _TIF_USING_IWMMXT	(1 << TIF_USING_IWMMXT)
 
 /* Checks for any syscall work in entry-common.S */
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 88336a1292bb..59a70d90b0b6 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -83,6 +83,8 @@ ENDPROC(ret_fast_syscall)
 
 	tst	r1, #_TIF_SYSCALL_WORK
 	bne	__sys_trace_return_nosave
+	tst	r1, #(_TIF_FD_SLOTS << 16)	@ r1 holds TI_FLAGS << 16
+	bne	__sys_trace_return_nosave
 slow_work_pending:
 	mov	r0, sp				@ 'regs'
 	mov	r2, why				@ 'syscall'
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index ed7a2a87a670..75fe26012fcb 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -11,6 +11,7 @@
 #include <linux/sched/task_stack.h>
 #include <linux/mm.h>
 #include <linux/elf.h>
+#include <linux/file.h>
 #include <linux/smp.h>
 #include <linux/ptrace.h>
 #include <linux/user.h>
@@ -876,6 +877,9 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs)
 
 asmlinkage void syscall_trace_exit(struct pt_regs *regs)
 {
+	if (test_thread_flag(TIF_FD_SLOTS))
+		fd_slots_commit(regs);
+
 	/*
 	 * Audit the syscall before anything else, as a debugger may
 	 * come in and change the current registers.

-- 
2.53.0