1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/ptrace.h> 3 #include <linux/sched.h> 4 #include <linux/sched/task_stack.h> 5 #include <linux/export.h> 6 #include <asm/syscall.h> 7 8 static int collect_syscall(struct task_struct *target, long *callno, 9 unsigned long args[6], unsigned int maxargs, 10 unsigned long *sp, unsigned long *pc) 11 { 12 struct pt_regs *regs; 13 14 if (!try_get_task_stack(target)) { 15 /* Task has no stack, so the task isn't in a syscall. */ 16 *sp = *pc = 0; 17 *callno = -1; 18 return 0; 19 } 20 21 regs = task_pt_regs(target); 22 if (unlikely(!regs)) { 23 put_task_stack(target); 24 return -EAGAIN; 25 } 26 27 *sp = user_stack_pointer(regs); 28 *pc = instruction_pointer(regs); 29 30 *callno = syscall_get_nr(target, regs); 31 if (*callno != -1L && maxargs > 0) 32 syscall_get_arguments(target, regs, 0, maxargs, args); 33 34 put_task_stack(target); 35 return 0; 36 } 37 38 /** 39 * task_current_syscall - Discover what a blocked task is doing. 40 * @target: thread to examine 41 * @callno: filled with system call number or -1 42 * @args: filled with @maxargs system call arguments 43 * @maxargs: number of elements in @args to fill 44 * @sp: filled with user stack pointer 45 * @pc: filled with user PC 46 * 47 * If @target is blocked in a system call, returns zero with *@callno 48 * set to the the call's number and @args filled in with its arguments. 49 * Registers not used for system call arguments may not be available and 50 * it is not kosher to use &struct user_regset calls while the system 51 * call is still in progress. Note we may get this result if @target 52 * has finished its system call but not yet returned to user mode, such 53 * as when it's stopped for signal handling or syscall exit tracing. 54 * 55 * If @target is blocked in the kernel during a fault or exception, 56 * returns zero with *@callno set to -1 and does not fill in @args. 57 * If so, it's now safe to examine @target using &struct user_regset 58 * get() calls as long as we're sure @target won't return to user mode. 59 * 60 * Returns -%EAGAIN if @target does not remain blocked. 61 * 62 * Returns -%EINVAL if @maxargs is too large (maximum is six). 63 */ 64 int task_current_syscall(struct task_struct *target, long *callno, 65 unsigned long args[6], unsigned int maxargs, 66 unsigned long *sp, unsigned long *pc) 67 { 68 long state; 69 unsigned long ncsw; 70 71 if (unlikely(maxargs > 6)) 72 return -EINVAL; 73 74 if (target == current) 75 return collect_syscall(target, callno, args, maxargs, sp, pc); 76 77 state = target->state; 78 if (unlikely(!state)) 79 return -EAGAIN; 80 81 ncsw = wait_task_inactive(target, state); 82 if (unlikely(!ncsw) || 83 unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) || 84 unlikely(wait_task_inactive(target, state) != ncsw)) 85 return -EAGAIN; 86 87 return 0; 88 } 89