1 files changed, 88 insertions, 0 deletions
diff --git a/lib/syscall.c b/lib/syscall.c
new file mode 100644
index 000000000..1a7077f20
--- /dev/null
+++ b/lib/syscall.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/ptrace.h>
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <linux/export.h>
+#include <asm/syscall.h>
+
+static int collect_syscall(struct task_struct *target, long *callno,
+			   unsigned long args[6], unsigned int maxargs,
+			   unsigned long *sp, unsigned long *pc)
+{
+	struct pt_regs *regs;
+
+	if (!try_get_task_stack(target)) {
+		/* Task has no stack, so the task isn't in a syscall. */
+		*sp = *pc = 0;
+		*callno = -1;
+		return 0;
+	}
+
+	regs = task_pt_regs(target);
+	if (unlikely(!regs)) {
+		put_task_stack(target);
+		return -EAGAIN;
+	}
+
+	*sp = user_stack_pointer(regs);
+	*pc = instruction_pointer(regs);
+
+	*callno = syscall_get_nr(target, regs);
+	if (*callno != -1L && maxargs > 0)
+		syscall_get_arguments(target, regs, 0, maxargs, args);
+
+	put_task_stack(target);
+	return 0;
+}
+
+/**
+ * task_current_syscall - Discover what a blocked task is doing.
+ * @target:		thread to examine
+ * @callno:		filled with system call number or -1
+ * @args:		filled with @maxargs system call arguments
+ * @maxargs:		number of elements in @args to fill
+ * @sp:			filled with user stack pointer
+ * @pc:			filled with user PC
+ *
+ * If @target is blocked in a system call, returns zero with *@callno
+ * set to the the call's number and @args filled in with its arguments.
+ * Registers not used for system call arguments may not be available and
+ * it is not kosher to use &struct user_regset calls while the system
+ * call is still in progress.  Note we may get this result if @target
+ * has finished its system call but not yet returned to user mode, such
+ * as when it's stopped for signal handling or syscall exit tracing.
+ *
+ * If @target is blocked in the kernel during a fault or exception,
+ * returns zero with *@callno set to -1 and does not fill in @args.
+ * If so, it's now safe to examine @target using &struct user_regset
+ * get() calls as long as we're sure @target won't return to user mode.
+ *
+ * Returns -%EAGAIN if @target does not remain blocked.
+ *
+ * Returns -%EINVAL if @maxargs is too large (maximum is six).
+ */
+int task_current_syscall(struct task_struct *target, long *callno,
+			 unsigned long args[6], unsigned int maxargs,
+			 unsigned long *sp, unsigned long *pc)
+{
+	long state;
+	unsigned long ncsw;
+
+	if (unlikely(maxargs > 6))
+		return -EINVAL;
+
+	if (target == current)
+		return collect_syscall(target, callno, args, maxargs, sp, pc);
+
+	state = target->state;
+	if (unlikely(!state))
+		return -EAGAIN;
+
+	ncsw = wait_task_inactive(target, state);
+	if (unlikely(!ncsw) ||
+	    unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
+	    unlikely(wait_task_inactive(target, state) != ncsw))
+		return -EAGAIN;
+
+	return 0;
+}