the-tree/lib/syscall.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 #include <linux/ptrace.h>
0003 #include <linux/sched.h>
0004 #include <linux/sched/task_stack.h>
0005 #include <linux/export.h>
0006 #include <asm/syscall.h>
0007
0008 static int collect_syscall(struct task_struct *target, struct syscall_info *info)
0009 {
0010     unsigned long args[6] = { };
0011     struct pt_regs *regs;
0012
0013     if (!try_get_task_stack(target)) {
0014         /* Task has no stack, so the task isn't in a syscall. */
0015         memset(info, 0, sizeof(*info));
0016         info->data.nr = -1;
0017         return 0;
0018     }
0019
0020     regs = task_pt_regs(target);
0021     if (unlikely(!regs)) {
0022         put_task_stack(target);
0023         return -EAGAIN;
0024     }
0025
0026     info->sp = user_stack_pointer(regs);
0027     info->data.instruction_pointer = instruction_pointer(regs);
0028
0029     info->data.nr = syscall_get_nr(target, regs);
0030     if (info->data.nr != -1L)
0031         syscall_get_arguments(target, regs, args);
0032
0033     info->data.args[0] = args[0];
0034     info->data.args[1] = args[1];
0035     info->data.args[2] = args[2];
0036     info->data.args[3] = args[3];
0037     info->data.args[4] = args[4];
0038     info->data.args[5] = args[5];
0039
0040     put_task_stack(target);
0041     return 0;
0042 }
0043
0044 /**
0045  * task_current_syscall - Discover what a blocked task is doing.
0046  * @target:     thread to examine
0047  * @info:       structure with the following fields:
0048  *           .sp        - filled with user stack pointer
0049  *           .data.nr   - filled with system call number or -1
0050  *           .data.args - filled with @maxargs system call arguments
0051  *           .data.instruction_pointer - filled with user PC
0052  *
0053  * If @target is blocked in a system call, returns zero with @info.data.nr
0054  * set to the call's number and @info.data.args filled in with its
0055  * arguments. Registers not used for system call arguments may not be available
0056  * and it is not kosher to use &struct user_regset calls while the system
0057  * call is still in progress.  Note we may get this result if @target
0058  * has finished its system call but not yet returned to user mode, such
0059  * as when it's stopped for signal handling or syscall exit tracing.
0060  *
0061  * If @target is blocked in the kernel during a fault or exception,
0062  * returns zero with *@info.data.nr set to -1 and does not fill in
0063  * @info.data.args. If so, it's now safe to examine @target using
0064  * &struct user_regset get() calls as long as we're sure @target won't return
0065  * to user mode.
0066  *
0067  * Returns -%EAGAIN if @target does not remain blocked.
0068  */
0069 int task_current_syscall(struct task_struct *target, struct syscall_info *info)
0070 {
0071     unsigned long ncsw;
0072     unsigned int state;
0073
0074     if (target == current)
0075         return collect_syscall(target, info);
0076
0077     state = READ_ONCE(target->__state);
0078     if (unlikely(!state))
0079         return -EAGAIN;
0080
0081     ncsw = wait_task_inactive(target, state);
0082     if (unlikely(!ncsw) ||
0083         unlikely(collect_syscall(target, info)) ||
0084         unlikely(wait_task_inactive(target, state) != ncsw))
0085         return -EAGAIN;
0086
0087     return 0;
0088 }