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