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entry: Add support for TIF_NOTIFY_SIGNAL
Add TIF_NOTIFY_SIGNAL handling in the generic entry code, which if set, will return true if signal_pending() is used in a wait loop. That causes an exit of the loop so that notify_signal tracehooks can be run. If the wait loop is currently inside a system call, the system call is restarted once task_work has been processed. In preparation for only having arch_do_signal() handle syscall restarts if _TIF_SIGPENDING isn't set, rename it to arch_do_signal_or_restart(). Pass in a boolean that tells the architecture specific signal handler if it should attempt to get a signal, or just process a potential syscall restart. For !CONFIG_GENERIC_ENTRY archs, add the TIF_NOTIFY_SIGNAL handling to get_signal(). This is done to minimize the needed architecture changes to support this feature. Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Link: https://lore.kernel.org/r/20201026203230.386348-3-axboe@kernel.dk
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@ -804,11 +804,11 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
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* want to handle. Thus you cannot kill init even with a SIGKILL even by
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* mistake.
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*/
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void arch_do_signal(struct pt_regs *regs)
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void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal)
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{
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struct ksignal ksig;
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if (get_signal(&ksig)) {
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if (has_signal && get_signal(&ksig)) {
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/* Whee! Actually deliver the signal. */
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handle_signal(&ksig, regs);
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return;
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@ -37,6 +37,10 @@
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# define _TIF_UPROBE (0)
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#endif
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#ifndef _TIF_NOTIFY_SIGNAL
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# define _TIF_NOTIFY_SIGNAL (0)
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#endif
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/*
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* TIF flags handled in syscall_enter_from_usermode()
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*/
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@ -69,7 +73,7 @@
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#define EXIT_TO_USER_MODE_WORK \
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(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
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_TIF_NEED_RESCHED | _TIF_PATCH_PENDING | \
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_TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \
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ARCH_EXIT_TO_USER_MODE_WORK)
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/**
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@ -226,12 +230,13 @@ static __always_inline void arch_exit_to_user_mode(void) { }
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#endif
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/**
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* arch_do_signal - Architecture specific signal delivery function
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* arch_do_signal_or_restart - Architecture specific signal delivery function
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* @regs: Pointer to currents pt_regs
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* @has_signal: actual signal to handle
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*
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* Invoked from exit_to_user_mode_loop().
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*/
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void arch_do_signal(struct pt_regs *regs);
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void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal);
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/**
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* arch_syscall_exit_tracehook - Wrapper around tracehook_report_syscall_exit()
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@ -11,8 +11,8 @@
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# define ARCH_XFER_TO_GUEST_MODE_WORK (0)
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#endif
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#define XFER_TO_GUEST_MODE_WORK \
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(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
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#define XFER_TO_GUEST_MODE_WORK \
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(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL | \
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_TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)
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struct kvm_vcpu;
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@ -360,6 +360,15 @@ static inline int task_sigpending(struct task_struct *p)
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static inline int signal_pending(struct task_struct *p)
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{
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#if defined(TIF_NOTIFY_SIGNAL)
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/*
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* TIF_NOTIFY_SIGNAL isn't really a signal, but it requires the same
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* behavior in terms of ensuring that we break out of wait loops
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* so that notify signal callbacks can be processed.
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*/
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if (unlikely(test_tsk_thread_flag(p, TIF_NOTIFY_SIGNAL)))
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return 1;
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#endif
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return task_sigpending(p);
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}
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@ -507,7 +516,7 @@ extern int set_user_sigmask(const sigset_t __user *umask, size_t sigsetsize);
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static inline void restore_saved_sigmask_unless(bool interrupted)
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{
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if (interrupted)
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WARN_ON(!test_thread_flag(TIF_SIGPENDING));
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WARN_ON(!signal_pending(current));
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else
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restore_saved_sigmask();
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}
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@ -198,4 +198,31 @@ static inline void tracehook_notify_resume(struct pt_regs *regs)
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blkcg_maybe_throttle_current();
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}
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/*
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* called by exit_to_user_mode_loop() if ti_work & _TIF_NOTIFY_SIGNAL. This
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* is currently used by TWA_SIGNAL based task_work, which requires breaking
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* wait loops to ensure that task_work is noticed and run.
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*/
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static inline void tracehook_notify_signal(void)
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{
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#if defined(TIF_NOTIFY_SIGNAL)
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clear_thread_flag(TIF_NOTIFY_SIGNAL);
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smp_mb__after_atomic();
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if (current->task_works)
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task_work_run();
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#endif
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}
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/*
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* Called when we have work to process from exit_to_user_mode_loop()
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*/
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static inline void set_notify_signal(struct task_struct *task)
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{
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#if defined(TIF_NOTIFY_SIGNAL)
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if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_SIGNAL) &&
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!wake_up_state(task, TASK_INTERRUPTIBLE))
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kick_process(task);
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#endif
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}
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#endif /* <linux/tracehook.h> */
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@ -109,7 +109,15 @@ static __always_inline void exit_to_user_mode(void)
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}
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/* Workaround to allow gradual conversion of architecture code */
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void __weak arch_do_signal(struct pt_regs *regs) { }
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void __weak arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal) { }
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static void handle_signal_work(struct pt_regs *regs, unsigned long ti_work)
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{
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if (ti_work & _TIF_NOTIFY_SIGNAL)
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tracehook_notify_signal();
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arch_do_signal_or_restart(regs, ti_work & _TIF_SIGPENDING);
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}
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static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
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unsigned long ti_work)
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@ -131,8 +139,8 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
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if (ti_work & _TIF_PATCH_PENDING)
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klp_update_patch_state(current);
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if (ti_work & _TIF_SIGPENDING)
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arch_do_signal(regs);
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if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
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handle_signal_work(regs, ti_work);
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if (ti_work & _TIF_NOTIFY_RESUME) {
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clear_thread_flag(TIF_NOTIFY_RESUME);
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@ -8,6 +8,9 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
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do {
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int ret;
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if (ti_work & _TIF_NOTIFY_SIGNAL)
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tracehook_notify_signal();
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if (ti_work & _TIF_SIGPENDING) {
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kvm_handle_signal_exit(vcpu);
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return -EINTR;
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@ -2529,6 +2529,20 @@ bool get_signal(struct ksignal *ksig)
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struct signal_struct *signal = current->signal;
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int signr;
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/*
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* For non-generic architectures, check for TIF_NOTIFY_SIGNAL so
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* that the arch handlers don't all have to do it. If we get here
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* without TIF_SIGPENDING, just exit after running signal work.
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*/
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#ifdef TIF_NOTIFY_SIGNAL
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if (!IS_ENABLED(CONFIG_GENERIC_ENTRY)) {
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if (test_thread_flag(TIF_NOTIFY_SIGNAL))
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tracehook_notify_signal();
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if (!task_sigpending(current))
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return false;
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}
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#endif
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if (unlikely(uprobe_deny_signal()))
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return false;
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