[PATCH v21 09/15] arm64: ptrace: Only run syscall exit work when exit work flags are set

[Jinjie Ruan]

Make the syscall exit path match generic entry, where
syscall_exit_work() is only called when one of the SYSCALL_WORK_EXIT
bits is set:

- Add _TIF_SYSCALL_EXIT_WORK for the thread flags that need work on
  syscall exit: trace, audit and tracepoint.

- Call the exit work from arm64_syscall_exit_to_user_mode_work() only
  when one of those flags or _TIF_SINGLESTEP is set.

- Rename syscall_trace_exit() to arm64_syscall_exit_work(), the arm64
  counterpart of syscall_exit_work().

- Move rseq_syscall() out of arm64_syscall_exit_work() into
  arm64_syscall_exit_to_user_mode_work(), so it still runs on every
  syscall exit and still runs before ptrace can change the PC, as in
  generic entry.

Checking _TIF_SYSCALL_AUDIT instead of calling audit_syscall_exit()
unconditionally is equivalent: the flag is set together with the audit
context at fork and neither changes while the task runs a system call.

No functional changes intended.

Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Ada Couprie Diaz <ada.coupriediaz@xxxxxxx>
Reviewed-by: Linus Walleij <linusw@xxxxxxxxxx>
Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
---
 arch/arm64/include/asm/syscall.h     | 8 ++++++--
 arch/arm64/include/asm/thread_info.h | 3 +++
 arch/arm64/kernel/ptrace.c           | 5 +----
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index 3e4672ab4a4f..7cc872fde019 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -8,6 +8,7 @@
 #include <uapi/linux/audit.h>
 #include <linux/compat.h>
 #include <linux/err.h>
+#include <linux/rseq.h>
 
 typedef long (*syscall_fn_t)(const struct pt_regs *regs);
 
@@ -121,13 +122,16 @@ static inline int syscall_get_arch(struct task_struct *task)
 }
 
 int arm64_syscall_trace_enter(struct pt_regs *regs, unsigned long flags);
-void syscall_trace_exit(struct pt_regs *regs, unsigned long flags);
+void arm64_syscall_exit_work(struct pt_regs *regs, unsigned long flags);
 
 static __always_inline void arm64_syscall_exit_to_user_mode_work(struct pt_regs *regs)
 {
 	unsigned long flags = read_thread_flags();
 
-	syscall_trace_exit(regs, flags);
+	rseq_syscall(regs);
+
+	if (unlikely(flags & _TIF_SYSCALL_EXIT_WORK) || flags & _TIF_SINGLESTEP)
+		arm64_syscall_exit_work(regs, flags);
 }
 
 #endif	/* __ASM_SYSCALL_H */
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 6cb976c1c693..a85c72b65b82 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -108,6 +108,9 @@ void arch_setup_new_exec(void);
 				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
 				 _TIF_SYSCALL_EMU)
 
+#define _TIF_SYSCALL_EXIT_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
+				 _TIF_SYSCALL_TRACEPOINT)
+
 #ifdef CONFIG_SHADOW_CALL_STACK
 #define INIT_SCS							\
 	.scs_base	= init_shadow_call_stack,			\
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 043f48ddc168..4c2bdd37d67d 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -28,7 +28,6 @@
 #include <linux/hw_breakpoint.h>
 #include <linux/regset.h>
 #include <linux/elf.h>
-#include <linux/rseq.h>
 
 #include <asm/compat.h>
 #include <asm/cpufeature.h>
@@ -2507,12 +2506,10 @@ static inline bool report_single_step(unsigned long flags)
 	return flags & _TIF_SINGLESTEP;
 }
 
-void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
+void arm64_syscall_exit_work(struct pt_regs *regs, unsigned long flags)
 {
 	bool step;
 
-	rseq_syscall(regs);
-
 	audit_syscall_exit(regs);
 
 	if (flags & _TIF_SYSCALL_TRACEPOINT)
-- 
2.34.1