MIPS: scall: Save thread_info.syscall unconditionally on entry

thread_info.syscall is used by syscall_get_nr to supply syscall nr
over a thread stack frame.

Previously, thread_info.syscall is only saved at syscall_trace_enter
when syscall tracing is enabled. However rest of the kernel code do
expect syscall_get_nr to be available without syscall tracing. The
previous design breaks collect_syscall.

Move saving process to syscall entry to fix it.

Reported-by: Xi Ruoyao <[e-mail]>
Link: https://github.com/util-linux/util-linux/issues/2867
Signed-off-by: Jiaxun Yang <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/include/asm/ptrace.h

···
 #define exception_ip(regs) exception_ip(regs)
 #define profile_pc(regs) instruction_pointer(regs)
 
-extern asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall);
+extern asmlinkage long syscall_trace_enter(struct pt_regs *regs);
 extern asmlinkage void syscall_trace_leave(struct pt_regs *regs);
 
 extern void die(const char *, struct pt_regs *) __noreturn;

arch/mips/kernel/asm-offsets.c

···
 	OFFSET(TI_CPU, thread_info, cpu);
 	OFFSET(TI_PRE_COUNT, thread_info, preempt_count);
 	OFFSET(TI_REGS, thread_info, regs);
+	OFFSET(TI_SYSCALL, thread_info, syscall);
 	DEFINE(_THREAD_SIZE, THREAD_SIZE);
 	DEFINE(_THREAD_MASK, THREAD_MASK);
 	DEFINE(_IRQ_STACK_SIZE, IRQ_STACK_SIZE);

arch/mips/kernel/ptrace.c

···
  * Notification of system call entry/exit
  * - triggered by current->work.syscall_trace
  */
-asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall)
+asmlinkage long syscall_trace_enter(struct pt_regs *regs)
 {
 	user_exit();
-
-	current_thread_info()->syscall = syscall;
 
 	if (test_thread_flag(TIF_SYSCALL_TRACE)) {
 		if (ptrace_report_syscall_entry(regs))
 			return -1;
-		syscall = current_thread_info()->syscall;
 	}
 
 #ifdef CONFIG_SECCOMP
···
 		struct seccomp_data sd;
 		unsigned long args[6];
 
-		sd.nr = syscall;
+		sd.nr = current_thread_info()->syscall;
 		sd.arch = syscall_get_arch(current);
 		syscall_get_arguments(current, regs, args);
 		for (i = 0; i < 6; i++)
···
 		ret = __secure_computing(&sd);
 		if (ret == -1)
 			return ret;
-		syscall = current_thread_info()->syscall;
 	}
 #endif
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 		trace_sys_enter(regs, regs->regs[2]);
 
-	audit_syscall_entry(syscall, regs->regs[4], regs->regs[5],
+	audit_syscall_entry(current_thread_info()->syscall,
+			    regs->regs[4], regs->regs[5],
 			    regs->regs[6], regs->regs[7]);
 
 	/*
 	 * Negative syscall numbers are mistaken for rejected syscalls, but
 	 * won't have had the return value set appropriately, so we do so now.
 	 */
-	if (syscall < 0)
+	if (current_thread_info()->syscall < 0)
 		syscall_set_return_value(current, regs, -ENOSYS, 0);
-	return syscall;
+	return current_thread_info()->syscall;
 }
 
 /*

arch/mips/kernel/scall32-o32.S

···
 	PTR_WD	load_a7, bad_stack_a7
 	.previous
 
+	/*
+	 * syscall number is in v0 unless we called syscall(__NR_###)
+	 * where the real syscall number is in a0
+	 */
+	subu	t2, v0,  __NR_O32_Linux
+	bnez	t2, 1f /* __NR_syscall at offset 0 */
+	LONG_S	a0, TI_SYSCALL($28)	# Save a0 as syscall number
+	b	2f
+1:
+	LONG_S	v0, TI_SYSCALL($28)	# Save v0 as syscall number
+2:
+
 	lw	t0, TI_FLAGS($28)	# syscall tracing enabled?
 	li	t1, _TIF_WORK_SYSCALL_ENTRY
 	and	t0, t1
···
 	SAVE_STATIC
 	move	a0, sp
 
-	/*
-	 * syscall number is in v0 unless we called syscall(__NR_###)
-	 * where the real syscall number is in a0
-	 */
-	move	a1, v0
-	subu	t2, v0,  __NR_O32_Linux
-	bnez	t2, 1f /* __NR_syscall at offset 0 */
-	lw	a1, PT_R4(sp)
-
-1:	jal	syscall_trace_enter
+	jal	syscall_trace_enter
 
 	bltz	v0, 1f			# seccomp failed? Skip syscall
 

arch/mips/kernel/scall64-n32.S

···
 
 	sd	a3, PT_R26(sp)		# save a3 for syscall restarting
 
+	LONG_S	v0, TI_SYSCALL($28)     # Store syscall number
+
 	li	t1, _TIF_WORK_SYSCALL_ENTRY
 	LONG_L	t0, TI_FLAGS($28)	# syscall tracing enabled?
 	and	t0, t1, t0
···
 n32_syscall_trace_entry:
 	SAVE_STATIC
 	move	a0, sp
-	move	a1, v0
 	jal	syscall_trace_enter
 
 	bltz	v0, 1f			# seccomp failed? Skip syscall

arch/mips/kernel/scall64-n64.S

···
 
 	sd	a3, PT_R26(sp)		# save a3 for syscall restarting
 
+	LONG_S	v0, TI_SYSCALL($28)     # Store syscall number
+
 	li	t1, _TIF_WORK_SYSCALL_ENTRY
 	LONG_L	t0, TI_FLAGS($28)	# syscall tracing enabled?
 	and	t0, t1, t0
···
 syscall_trace_entry:
 	SAVE_STATIC
 	move	a0, sp
-	move	a1, v0
 	jal	syscall_trace_enter
 
 	bltz	v0, 1f			# seccomp failed? Skip syscall

arch/mips/kernel/scall64-o32.S

···
 	PTR_WD	load_a7, bad_stack_a7
 	.previous
 
+	/*
+	 * absolute syscall number is in v0 unless we called syscall(__NR_###)
+	 * where the real syscall number is in a0
+	 * note: NR_syscall is the first O32 syscall but the macro is
+	 * only defined when compiling with -mabi=32 (CONFIG_32BIT)
+	 * therefore __NR_O32_Linux is used (4000)
+	 */
+
+	subu	t2, v0,  __NR_O32_Linux
+	bnez	t2, 1f /* __NR_syscall at offset 0 */
+	LONG_S	a0, TI_SYSCALL($28)	# Save a0 as syscall number
+	b	2f
+1:
+	LONG_S	v0, TI_SYSCALL($28)	# Save v0 as syscall number
+2:
+
 	li	t1, _TIF_WORK_SYSCALL_ENTRY
 	LONG_L	t0, TI_FLAGS($28)	# syscall tracing enabled?
 	and	t0, t1, t0
···
 	sd	a7, PT_R11(sp)		# For indirect syscalls
 
 	move	a0, sp
-	/*
-	 * absolute syscall number is in v0 unless we called syscall(__NR_###)
-	 * where the real syscall number is in a0
-	 * note: NR_syscall is the first O32 syscall but the macro is
-	 * only defined when compiling with -mabi=32 (CONFIG_32BIT)
-	 * therefore __NR_O32_Linux is used (4000)
-	 */
-	.set	push
-	.set	reorder
-	subu	t1, v0,  __NR_O32_Linux
-	move	a1, v0
-	bnez	t1, 1f /* __NR_syscall at offset 0 */
-	ld	a1, PT_R4(sp) /* Arg1 for __NR_syscall case */
-	.set	pop
-
-1:	jal	syscall_trace_enter
+	jal	syscall_trace_enter
 
 	bltz	v0, 1f			# seccomp failed? Skip syscall