| 1 | #include <linux/ptrace.h>
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| 2 | #include <linux/sched.h>
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| 3 | #include <linux/sched/task_stack.h>
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| 4 | #include <linux/export.h>
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| 5 | #include <asm/syscall.h>
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| 6 |
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| 7 | static int collect_syscall(struct task_struct *target, long *callno,
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| 8 | unsigned long args[6], unsigned int maxargs,
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| 9 | unsigned long *sp, unsigned long *pc)
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| 10 | {
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| 11 | struct pt_regs *regs;
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| 12 |
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| 13 | if (!try_get_task_stack(target)) {
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| 14 |
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| 15 | *sp = *pc = 0;
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| 16 | *callno = -1;
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| 17 | return 0;
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| 18 | }
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| 19 |
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| 20 | regs = task_pt_regs(target);
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| 21 | if (unlikely(!regs)) {
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| 22 | put_task_stack(target);
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| 23 | return -EAGAIN;
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| 24 | }
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| 25 |
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| 26 | *sp = user_stack_pointer(regs);
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| 27 | *pc = instruction_pointer(regs);
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| 28 |
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| 29 | *callno = syscall_get_nr(target, regs);
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| 30 | if (*callno != -1L && maxargs > 0)
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| 31 | syscall_get_arguments(target, regs, 0, maxargs, args);
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| 32 |
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| 33 | put_task_stack(target);
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| 34 | return 0;
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| 35 | }
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| 36 |
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| 37 | |
| 38 | * task_current_syscall - Discover what a blocked task is doing.
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| 39 | * @target: thread to examine
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| 40 | * @callno: filled with system call number or -1
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| 41 | * @args: filled with @maxargs system call arguments
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| 42 | * @maxargs: number of elements in @args to fill
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| 43 | * @sp: filled with user stack pointer
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| 44 | * @pc: filled with user PC
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| 45 | *
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| 46 | * If @target is blocked in a system call, returns zero with *@callno
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| 47 | * set to the the call's number and @args filled in with its arguments.
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| 48 | * Registers not used for system call arguments may not be available and
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| 49 | * it is not kosher to use &struct user_regset calls while the system
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| 50 | * call is still in progress. Note we may get this result if @target
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| 51 | * has finished its system call but not yet returned to user mode, such
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| 52 | * as when it's stopped for signal handling or syscall exit tracing.
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| 53 | *
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| 54 | * If @target is blocked in the kernel during a fault or exception,
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| 55 | * returns zero with *@callno set to -1 and does not fill in @args.
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| 56 | * If so, it's now safe to examine @target using &struct user_regset
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| 57 | * get() calls as long as we're sure @target won't return to user mode.
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| 58 | *
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| 59 | * Returns -%EAGAIN if @target does not remain blocked.
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| 60 | *
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| 61 | * Returns -%EINVAL if @maxargs is too large (maximum is six).
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| 62 |
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| 63 | int task_current_syscall(struct task_struct *target, long *callno,
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| 64 | unsigned long args[6], unsigned int maxargs,
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| 65 | unsigned long *sp, unsigned long *pc)
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| 66 | {
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| 67 | long state;
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| 68 | unsigned long ncsw;
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| 69 |
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| 70 | if (unlikely(maxargs > 6))
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| 71 | return -EINVAL;
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| 72 |
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| 73 | if (target == current)
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| 74 | return collect_syscall(target, callno, args, maxargs, sp, pc);
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| 75 |
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| 76 | state = target->state;
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| 77 | if (unlikely(!state))
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| 78 | return -EAGAIN;
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| 79 |
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| 80 | ncsw = wait_task_inactive(target, state);
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| 81 | if (unlikely(!ncsw) ||
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| 82 | unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
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| 83 | unlikely(wait_task_inactive(target, state) != ncsw))
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| 84 | return -EAGAIN;
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| 85 |
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| 86 | return 0;
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| 87 | }
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