![Tejun Heo](/assets/img/avatar_default.png)
At this point, tracehooks aren't useful to mainline kernel and mostly just add an extra layer of obfuscation. Although they have comments, without actual in-kernel users, it is difficult to tell what are their assumptions and they're actually trying to achieve. To mainline kernel, they just aren't worth keeping around. This patch kills the following trivial tracehooks. * Ones testing whether task is ptraced. Replace with ->ptrace test. tracehook_expect_breakpoints() tracehook_consider_ignored_signal() tracehook_consider_fatal_signal() * ptrace_event() wrappers. Call directly. tracehook_report_exec() tracehook_report_exit() tracehook_report_vfork_done() * ptrace_release_task() wrapper. Call directly. tracehook_finish_release_task() * noop tracehook_prepare_release_task() tracehook_report_death() This doesn't introduce any behavior change. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
363 lines
13 KiB
C
363 lines
13 KiB
C
/*
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* Tracing hooks
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*
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* Copyright (C) 2008-2009 Red Hat, Inc. All rights reserved.
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*
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* This copyrighted material is made available to anyone wishing to use,
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* modify, copy, or redistribute it subject to the terms and conditions
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* of the GNU General Public License v.2.
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*
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* This file defines hook entry points called by core code where
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* user tracing/debugging support might need to do something. These
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* entry points are called tracehook_*(). Each hook declared below
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* has a detailed kerneldoc comment giving the context (locking et
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* al) from which it is called, and the meaning of its return value.
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*
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* Each function here typically has only one call site, so it is ok
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* to have some nontrivial tracehook_*() inlines. In all cases, the
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* fast path when no tracing is enabled should be very short.
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*
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* The purpose of this file and the tracehook_* layer is to consolidate
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* the interface that the kernel core and arch code uses to enable any
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* user debugging or tracing facility (such as ptrace). The interfaces
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* here are carefully documented so that maintainers of core and arch
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* code do not need to think about the implementation details of the
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* tracing facilities. Likewise, maintainers of the tracing code do not
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* need to understand all the calling core or arch code in detail, just
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* documented circumstances of each call, such as locking conditions.
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*
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* If the calling core code changes so that locking is different, then
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* it is ok to change the interface documented here. The maintainer of
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* core code changing should notify the maintainers of the tracing code
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* that they need to work out the change.
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*
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* Some tracehook_*() inlines take arguments that the current tracing
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* implementations might not necessarily use. These function signatures
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* are chosen to pass in all the information that is on hand in the
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* caller and might conceivably be relevant to a tracer, so that the
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* core code won't have to be updated when tracing adds more features.
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* If a call site changes so that some of those parameters are no longer
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* already on hand without extra work, then the tracehook_* interface
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* can change so there is no make-work burden on the core code. The
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* maintainer of core code changing should notify the maintainers of the
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* tracing code that they need to work out the change.
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*/
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#ifndef _LINUX_TRACEHOOK_H
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#define _LINUX_TRACEHOOK_H 1
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#include <linux/sched.h>
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#include <linux/ptrace.h>
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#include <linux/security.h>
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struct linux_binprm;
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/*
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* ptrace report for syscall entry and exit looks identical.
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*/
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static inline void ptrace_report_syscall(struct pt_regs *regs)
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{
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int ptrace = current->ptrace;
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if (!(ptrace & PT_PTRACED))
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return;
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ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
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/*
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* this isn't the same as continuing with a signal, but it will do
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* for normal use. strace only continues with a signal if the
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* stopping signal is not SIGTRAP. -brl
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*/
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if (current->exit_code) {
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send_sig(current->exit_code, current, 1);
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current->exit_code = 0;
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}
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}
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/**
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* tracehook_report_syscall_entry - task is about to attempt a system call
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* @regs: user register state of current task
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*
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* This will be called if %TIF_SYSCALL_TRACE has been set, when the
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* current task has just entered the kernel for a system call.
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* Full user register state is available here. Changing the values
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* in @regs can affect the system call number and arguments to be tried.
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* It is safe to block here, preventing the system call from beginning.
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*
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* Returns zero normally, or nonzero if the calling arch code should abort
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* the system call. That must prevent normal entry so no system call is
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* made. If @task ever returns to user mode after this, its register state
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* is unspecified, but should be something harmless like an %ENOSYS error
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* return. It should preserve enough information so that syscall_rollback()
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* can work (see asm-generic/syscall.h).
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*
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* Called without locks, just after entering kernel mode.
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*/
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static inline __must_check int tracehook_report_syscall_entry(
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struct pt_regs *regs)
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{
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ptrace_report_syscall(regs);
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return 0;
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}
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/**
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* tracehook_report_syscall_exit - task has just finished a system call
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* @regs: user register state of current task
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* @step: nonzero if simulating single-step or block-step
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*
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* This will be called if %TIF_SYSCALL_TRACE has been set, when the
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* current task has just finished an attempted system call. Full
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* user register state is available here. It is safe to block here,
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* preventing signals from being processed.
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*
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* If @step is nonzero, this report is also in lieu of the normal
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* trap that would follow the system call instruction because
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* user_enable_block_step() or user_enable_single_step() was used.
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* In this case, %TIF_SYSCALL_TRACE might not be set.
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*
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* Called without locks, just before checking for pending signals.
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*/
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static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
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{
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if (step) {
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siginfo_t info;
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user_single_step_siginfo(current, regs, &info);
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force_sig_info(SIGTRAP, &info, current);
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return;
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}
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ptrace_report_syscall(regs);
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}
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/**
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* tracehook_unsafe_exec - check for exec declared unsafe due to tracing
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* @task: current task doing exec
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*
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* Return %LSM_UNSAFE_* bits applied to an exec because of tracing.
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*
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* @task->signal->cred_guard_mutex is held by the caller through the do_execve().
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*/
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static inline int tracehook_unsafe_exec(struct task_struct *task)
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{
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int unsafe = 0;
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int ptrace = task->ptrace;
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if (ptrace & PT_PTRACED) {
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if (ptrace & PT_PTRACE_CAP)
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unsafe |= LSM_UNSAFE_PTRACE_CAP;
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else
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unsafe |= LSM_UNSAFE_PTRACE;
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}
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return unsafe;
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}
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/**
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* tracehook_tracer_task - return the task that is tracing the given task
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* @tsk: task to consider
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*
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* Returns NULL if no one is tracing @task, or the &struct task_struct
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* pointer to its tracer.
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*
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* Must called under rcu_read_lock(). The pointer returned might be kept
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* live only by RCU. During exec, this may be called with task_lock()
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* held on @task, still held from when tracehook_unsafe_exec() was called.
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*/
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static inline struct task_struct *tracehook_tracer_task(struct task_struct *tsk)
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{
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if (tsk->ptrace & PT_PTRACED)
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return rcu_dereference(tsk->parent);
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return NULL;
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}
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/**
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* tracehook_prepare_clone - prepare for new child to be cloned
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* @clone_flags: %CLONE_* flags from clone/fork/vfork system call
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*
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* This is called before a new user task is to be cloned.
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* Its return value will be passed to tracehook_finish_clone().
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*
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* Called with no locks held.
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*/
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static inline int tracehook_prepare_clone(unsigned clone_flags)
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{
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int event = 0;
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if (clone_flags & CLONE_UNTRACED)
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return 0;
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if (clone_flags & CLONE_VFORK)
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event = PTRACE_EVENT_VFORK;
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else if ((clone_flags & CSIGNAL) != SIGCHLD)
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event = PTRACE_EVENT_CLONE;
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else
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event = PTRACE_EVENT_FORK;
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return ptrace_event_enabled(current, event) ? event : 0;
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}
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/**
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* tracehook_finish_clone - new child created and being attached
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* @child: new child task
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* @clone_flags: %CLONE_* flags from clone/fork/vfork system call
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* @trace: return value from tracehook_prepare_clone()
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*
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* This is called immediately after adding @child to its parent's children list.
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* The @trace value is that returned by tracehook_prepare_clone().
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*
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* Called with current's siglock and write_lock_irq(&tasklist_lock) held.
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*/
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static inline void tracehook_finish_clone(struct task_struct *child,
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unsigned long clone_flags, int trace)
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{
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ptrace_init_task(child, (clone_flags & CLONE_PTRACE) || trace);
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}
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/**
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* tracehook_report_clone - in parent, new child is about to start running
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* @regs: parent's user register state
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* @clone_flags: flags from parent's system call
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* @pid: new child's PID in the parent's namespace
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* @child: new child task
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*
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* Called after a child is set up, but before it has been started running.
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* This is not a good place to block, because the child has not started
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* yet. Suspend the child here if desired, and then block in
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* tracehook_report_clone_complete(). This must prevent the child from
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* self-reaping if tracehook_report_clone_complete() uses the @child
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* pointer; otherwise it might have died and been released by the time
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* tracehook_report_clone_complete() is called.
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*
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* Called with no locks held, but the child cannot run until this returns.
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*/
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static inline void tracehook_report_clone(struct pt_regs *regs,
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unsigned long clone_flags,
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pid_t pid, struct task_struct *child)
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{
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if (unlikely(child->ptrace)) {
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/*
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* It doesn't matter who attached/attaching to this
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* task, the pending SIGSTOP is right in any case.
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*/
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sigaddset(&child->pending.signal, SIGSTOP);
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set_tsk_thread_flag(child, TIF_SIGPENDING);
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}
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}
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/**
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* tracehook_report_clone_complete - new child is running
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* @trace: return value from tracehook_prepare_clone()
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* @regs: parent's user register state
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* @clone_flags: flags from parent's system call
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* @pid: new child's PID in the parent's namespace
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* @child: child task, already running
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*
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* This is called just after the child has started running. This is
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* just before the clone/fork syscall returns, or blocks for vfork
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* child completion if @clone_flags has the %CLONE_VFORK bit set.
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* The @child pointer may be invalid if a self-reaping child died and
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* tracehook_report_clone() took no action to prevent it from self-reaping.
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*
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* Called with no locks held.
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*/
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static inline void tracehook_report_clone_complete(int trace,
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struct pt_regs *regs,
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unsigned long clone_flags,
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pid_t pid,
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struct task_struct *child)
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{
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if (unlikely(trace))
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ptrace_event(trace, pid);
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}
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/**
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* tracehook_signal_handler - signal handler setup is complete
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* @sig: number of signal being delivered
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* @info: siginfo_t of signal being delivered
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* @ka: sigaction setting that chose the handler
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* @regs: user register state
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* @stepping: nonzero if debugger single-step or block-step in use
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*
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* Called by the arch code after a signal handler has been set up.
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* Register and stack state reflects the user handler about to run.
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* Signal mask changes have already been made.
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*
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* Called without locks, shortly before returning to user mode
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* (or handling more signals).
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*/
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static inline void tracehook_signal_handler(int sig, siginfo_t *info,
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const struct k_sigaction *ka,
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struct pt_regs *regs, int stepping)
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{
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if (stepping)
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ptrace_notify(SIGTRAP);
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}
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#define DEATH_REAP -1
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#define DEATH_DELAYED_GROUP_LEADER -2
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/**
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* tracehook_notify_death - task is dead, ready to notify parent
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* @task: @current task now exiting
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* @death_cookie: value to pass to tracehook_report_death()
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* @group_dead: nonzero if this was the last thread in the group to die
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*
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* A return value >= 0 means call do_notify_parent() with that signal
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* number. Negative return value can be %DEATH_REAP to self-reap right
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* now, or %DEATH_DELAYED_GROUP_LEADER to a zombie without notifying our
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* parent. Note that a return value of 0 means a do_notify_parent() call
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* that sends no signal, but still wakes up a parent blocked in wait*().
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*
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* Called with write_lock_irq(&tasklist_lock) held.
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*/
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static inline int tracehook_notify_death(struct task_struct *task,
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void **death_cookie, int group_dead)
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{
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if (task_detached(task))
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return task->ptrace ? SIGCHLD : DEATH_REAP;
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/*
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* If something other than our normal parent is ptracing us, then
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* send it a SIGCHLD instead of honoring exit_signal. exit_signal
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* only has special meaning to our real parent.
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*/
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if (thread_group_empty(task) && !ptrace_reparented(task))
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return task->exit_signal;
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return task->ptrace ? SIGCHLD : DEATH_DELAYED_GROUP_LEADER;
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}
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#ifdef TIF_NOTIFY_RESUME
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/**
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* set_notify_resume - cause tracehook_notify_resume() to be called
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* @task: task that will call tracehook_notify_resume()
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*
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* Calling this arranges that @task will call tracehook_notify_resume()
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* before returning to user mode. If it's already running in user mode,
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* it will enter the kernel and call tracehook_notify_resume() soon.
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* If it's blocked, it will not be woken.
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*/
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static inline void set_notify_resume(struct task_struct *task)
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{
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if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
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kick_process(task);
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}
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/**
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* tracehook_notify_resume - report when about to return to user mode
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* @regs: user-mode registers of @current task
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*
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* This is called when %TIF_NOTIFY_RESUME has been set. Now we are
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* about to return to user mode, and the user state in @regs can be
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* inspected or adjusted. The caller in arch code has cleared
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* %TIF_NOTIFY_RESUME before the call. If the flag gets set again
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* asynchronously, this will be called again before we return to
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* user mode.
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*
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* Called without locks.
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*/
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static inline void tracehook_notify_resume(struct pt_regs *regs)
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{
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}
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#endif /* TIF_NOTIFY_RESUME */
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#endif /* <linux/tracehook.h> */
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