From 16cc1bc67de88be19fa595f4645506ea2ac106d2 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 29 Apr 2022 11:09:11 -0500 Subject: ptrace: Remove arch_ptrace_attach The last remaining implementation of arch_ptrace_attach is ia64's ptrace_attach_sync_user_rbs which was added at the end of 2007 in commit aa91a2e90044 ("[IA64] Synchronize RBS on PTRACE_ATTACH"). Reading the comments and examining the code ptrace_attach_sync_user_rbs has the sole purpose of saving registers to the stack when ptrace_attach changes TASK_STOPPED to TASK_TRACED. In all other cases arch_ptrace_stop takes care of the register saving. In commit d79fdd6d96f4 ("ptrace: Clean transitions between TASK_STOPPED and TRACED") modified ptrace_attach to wake up the thread and enter ptrace_stop normally even when the thread starts out stopped. This makes ptrace_attach_sync_user_rbs completely unnecessary. So just remove it. I read through the code to verify that ptrace_attach_sync_user_rbs is unnecessary. What I found is that the code is quite dead. Reading ptrace_attach_sync_user_rbs it is easy to see that the it does nothing unless __state == TASK_STOPPED. Calling arch_ptrace_attach (aka ptrace_attach_sync_user_rbs) after ptrace_traceme it is easy to see that because we are talking about the current process the value of __state is TASK_RUNNING. Which means ptrace_attach_sync_user_rbs does nothing. The only other call of arch_ptrace_attach (aka ptrace_attach_sync_user_rbs) is after ptrace_attach. If the task is running (and PTRACE_SEIZE is not specified), a SIGSTOP is sent which results in do_signal_stop setting JOBCTL_TRAP_STOP on the target task (as it is ptraced) and the target task stopping in ptrace_stop with __state == TASK_TRACED. If the task was already stopped then ptrace_attach sets JOBCTL_TRAPPING and JOBCTL_TRAP_STOP, wakes it out of __TASK_STOPPED, and waits until the JOBCTL_TRAPPING_BIT is clear. At which point the task stops in ptrace_stop. In both cases there are a couple of funning excpetions such as if the traced task receiveds a SIGCONT, or is set a fatal signal. However in all of those cases the tracee never stops in __state TASK_STOPPED. Which is a long way of saying that ptrace_attach_sync_user_rbs is guaranteed never to do anything. Cc: linux-ia64@vger.kernel.org Tested-by: Kees Cook Reviewed-by: Oleg Nesterov Link: https://lkml.kernel.org/r/20220505182645.497868-4-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman" --- arch/ia64/kernel/ptrace.c | 57 ----------------------------------------------- 1 file changed, 57 deletions(-) (limited to 'arch/ia64/kernel') diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c index a19acd9f5e1f..a45f529046c3 100644 --- a/arch/ia64/kernel/ptrace.c +++ b/arch/ia64/kernel/ptrace.c @@ -617,63 +617,6 @@ void ia64_sync_krbs(void) unw_init_running(do_sync_rbs, ia64_sync_kernel_rbs); } -/* - * After PTRACE_ATTACH, a thread's register backing store area in user - * space is assumed to contain correct data whenever the thread is - * stopped. arch_ptrace_stop takes care of this on tracing stops. - * But if the child was already stopped for job control when we attach - * to it, then it might not ever get into ptrace_stop by the time we - * want to examine the user memory containing the RBS. - */ -void -ptrace_attach_sync_user_rbs (struct task_struct *child) -{ - int stopped = 0; - struct unw_frame_info info; - - /* - * If the child is in TASK_STOPPED, we need to change that to - * TASK_TRACED momentarily while we operate on it. This ensures - * that the child won't be woken up and return to user mode while - * we are doing the sync. (It can only be woken up for SIGKILL.) - */ - - read_lock(&tasklist_lock); - if (child->sighand) { - spin_lock_irq(&child->sighand->siglock); - if (READ_ONCE(child->__state) == TASK_STOPPED && - !test_and_set_tsk_thread_flag(child, TIF_RESTORE_RSE)) { - set_notify_resume(child); - - WRITE_ONCE(child->__state, TASK_TRACED); - stopped = 1; - } - spin_unlock_irq(&child->sighand->siglock); - } - read_unlock(&tasklist_lock); - - if (!stopped) - return; - - unw_init_from_blocked_task(&info, child); - do_sync_rbs(&info, ia64_sync_user_rbs); - - /* - * Now move the child back into TASK_STOPPED if it should be in a - * job control stop, so that SIGCONT can be used to wake it up. - */ - read_lock(&tasklist_lock); - if (child->sighand) { - spin_lock_irq(&child->sighand->siglock); - if (READ_ONCE(child->__state) == TASK_TRACED && - (child->signal->flags & SIGNAL_STOP_STOPPED)) { - WRITE_ONCE(child->__state, TASK_STOPPED); - } - spin_unlock_irq(&child->sighand->siglock); - } - read_unlock(&tasklist_lock); -} - /* * Write f32-f127 back to task->thread.fph if it has been modified. */ -- cgit v1.2.3-59-g8ed1b