kernel/include/linux/sched/signal.h, branch linux-6.1.y

posix-timers: Ensure timer ID search-loop limit is valid

2024-08-29T15:30:17Z

[ Upstream commit 8ce8849dd1e78dadcee0ec9acbd259d239b7069f ] posix_timer_add() tries to allocate a posix timer ID by starting from the cached ID which was stored by the last successful allocation. This is done in a loop searching the ID space for a free slot one by one. The loop has to terminate when the search wrapped around to the starting point. But that's racy vs. establishing the starting point. That is read out lockless, which leads to the following problem: CPU0 CPU1 posix_timer_add() start = sig->posix_timer_id; lock(hash_lock); ... posix_timer_add() if (++sig->posix_timer_id < 0) start = sig->posix_timer_id; sig->posix_timer_id = 0; So CPU1 can observe a negative start value, i.e. -1, and the loop break never happens because the condition can never be true: if (sig->posix_timer_id == start) break; While this is unlikely to ever turn into an endless loop as the ID space is huge (INT_MAX), the racy read of the start value caught the attention of KCSAN and Dmitry unearthed that incorrectness. Rewrite it so that all id operations are under the hash lock. Reported-by: syzbot+5c54bd3eb218bb595aa9@syzkaller.appspotmail.com Reported-by: Dmitry Vyukov Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lore.kernel.org/r/87bkhzdn6g.ffs@tglx Signed-off-by: Sasha Levin

signal: Guarantee that SIGNAL_GROUP_EXIT is set on process exit

2022-07-20T15:23:51Z

Track how many threads have not started exiting and when the last thread starts exiting set SIGNAL_GROUP_EXIT. This guarantees that SIGNAL_GROUP_EXIT will get set when a process exits. In practice this achieves nothing as glibc's implementation of _exit calls sys_group_exit then sys_exit. While glibc's implemenation of pthread_exit calls exit (which cleansup and calls _exit) if it is the last thread and sys_exit if it is the last thread. This means the only way the kernel might observe a process that does not set call exit_group is if the language runtime does not use glibc. With more cleanups I hope to move the decrement of quick_threads earlier. Link: https://lkml.kernel.org/r/87bkukd4tc.fsf_-_@email.froward.int.ebiederm.org Signed-off-by: "Eric W. Biederman"

Merge tag 'ptrace_stop-cleanup-for-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2022-06-03T23:13:25Z

Pull ptrace_stop cleanups from Eric Biederman: "While looking at the ptrace problems with PREEMPT_RT and the problems Peter Zijlstra was encountering with ptrace in his freezer rewrite I identified some cleanups to ptrace_stop that make sense on their own and move make resolving the other problems much simpler. The biggest issue is the habit of the ptrace code to change task->__state from the tracer to suppress TASK_WAKEKILL from waking up the tracee. No other code in the kernel does that and it is straight forward to update signal_wake_up and friends to make that unnecessary. Peter's task freezer sets frozen tasks to a new state TASK_FROZEN and then it stores them by calling "wake_up_state(t, TASK_FROZEN)" relying on the fact that all stopped states except the special stop states can tolerate spurious wake up and recover their state. The state of stopped and traced tasked is changed to be stored in task->jobctl as well as in task->__state. This makes it possible for the freezer to recover tasks in these special states, as well as serving as a general cleanup. With a little more work in that direction I believe TASK_STOPPED can learn to tolerate spurious wake ups and become an ordinary stop state. The TASK_TRACED state has to remain a special state as the registers for a process are only reliably available when the process is stopped in the scheduler. Fundamentally ptrace needs acess to the saved register values of a task. There are bunch of semi-random ptrace related cleanups that were found while looking at these issues. One cleanup that deserves to be called out is from commit 57b6de08b5f6 ("ptrace: Admit ptrace_stop can generate spuriuos SIGTRAPs"). This makes a change that is technically user space visible, in the handling of what happens to a tracee when a tracer dies unexpectedly. According to our testing and our understanding of userspace nothing cares that spurious SIGTRAPs can be generated in that case" * tag 'ptrace_stop-cleanup-for-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state ptrace: Always take siglock in ptrace_resume ptrace: Don't change __state ptrace: Admit ptrace_stop can generate spuriuos SIGTRAPs ptrace: Document that wait_task_inactive can't fail ptrace: Reimplement PTRACE_KILL by always sending SIGKILL signal: Use lockdep_assert_held instead of assert_spin_locked ptrace: Remove arch_ptrace_attach ptrace/xtensa: Replace PT_SINGLESTEP with TIF_SINGLESTEP ptrace/um: Replace PT_DTRACE with TIF_SINGLESTEP signal: Replace __group_send_sig_info with send_signal_locked signal: Rename send_signal send_signal_locked

Merge tag 'perf-core-2022-05-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-05-24T17:59:38Z

Pull perf events updates from Ingo Molnar: "Platform PMU changes: - x86/intel: - Add new Intel Alder Lake and Raptor Lake support - x86/amd: - AMD Zen4 IBS extensions support - Add AMD PerfMonV2 support - Add AMD Fam19h Branch Sampling support Generic changes: - signal: Deliver SIGTRAP on perf event asynchronously if blocked Perf instrumentation can be driven via SIGTRAP, but this causes a problem when SIGTRAP is blocked by a task & terminate the task. Allow user-space to request these signals asynchronously (after they get unblocked) & also give the information to the signal handler when this happens: "To give user space the ability to clearly distinguish synchronous from asynchronous signals, introduce siginfo_t::si_perf_flags and TRAP_PERF_FLAG_ASYNC (opted for flags in case more binary information is required in future). The resolution to the problem is then to (a) no longer force the signal (avoiding the terminations), but (b) tell user space via si_perf_flags if the signal was synchronous or not, so that such signals can be handled differently (e.g. let user space decide to ignore or consider the data imprecise). " - Unify/standardize the /sys/devices/cpu/events/* output format. - Misc fixes & cleanups" * tag 'perf-core-2022-05-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (32 commits) perf/x86/amd/core: Fix reloading events for SVM perf/x86/amd: Run AMD BRS code only on supported hw perf/x86/amd: Fix AMD BRS period adjustment perf/x86/amd: Remove unused variable 'hwc' perf/ibs: Fix comment perf/amd/ibs: Advertise zen4_ibs_extensions as pmu capability attribute perf/amd/ibs: Add support for L3 miss filtering perf/amd/ibs: Use ->is_visible callback for dynamic attributes perf/amd/ibs: Cascade pmu init functions' return value perf/x86/uncore: Add new Alder Lake and Raptor Lake support perf/x86/uncore: Clean up uncore_pci_ids[] perf/x86/cstate: Add new Alder Lake and Raptor Lake support perf/x86/msr: Add new Alder Lake and Raptor Lake support perf/x86: Add new Alder Lake and Raptor Lake support perf/amd/ibs: Use interrupt regs ip for stack unwinding perf/x86/amd/core: Add PerfMonV2 overflow handling perf/x86/amd/core: Add PerfMonV2 counter control perf/x86/amd/core: Detect available counters perf/x86/amd/core: Detect PerfMonV2 support x86/msr: Add PerfCntrGlobal* registers ...

sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state

2022-05-11T19:37:06Z

Currently ptrace_stop() / do_signal_stop() rely on the special states TASK_TRACED and TASK_STOPPED resp. to keep unique state. That is, this state exists only in task->__state and nowhere else. There's two spots of bother with this: - PREEMPT_RT has task->saved_state which complicates matters, meaning task_is_{traced,stopped}() needs to check an additional variable. - An alternative freezer implementation that itself relies on a special TASK state would loose TASK_TRACED/TASK_STOPPED and will result in misbehaviour. As such, add additional state to task->jobctl to track this state outside of task->__state. NOTE: this doesn't actually fix anything yet, just adds extra state. --EWB * didn't add a unnecessary newline in signal.h * Update t->jobctl in signal_wake_up and ptrace_signal_wake_up instead of in signal_wake_up_state. This prevents the clearing of TASK_STOPPED and TASK_TRACED from getting lost. * Added warnings if JOBCTL_STOPPED or JOBCTL_TRACED are not cleared Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20220421150654.757693825@infradead.org Tested-by: Kees Cook Reviewed-by: Oleg Nesterov Link: https://lkml.kernel.org/r/20220505182645.497868-12-ebiederm@xmission.com Signed-off-by: Eric W. Biederman

ptrace: Don't change __state

2022-05-11T19:35:32Z

Stop playing with tsk->__state to remove TASK_WAKEKILL while a ptrace command is executing. Instead remove TASK_WAKEKILL from the definition of TASK_TRACED, and implement a new jobctl flag TASK_PTRACE_FROZEN. This new flag is set in jobctl_freeze_task and cleared when ptrace_stop is awoken or in jobctl_unfreeze_task (when ptrace_stop remains asleep). In signal_wake_up add __TASK_TRACED to state along with TASK_WAKEKILL when the wake up is for a fatal signal. Skip adding __TASK_TRACED when TASK_PTRACE_FROZEN is not set. This has the same effect as changing TASK_TRACED to __TASK_TRACED as all of the wake_ups that use TASK_KILLABLE go through signal_wake_up. Handle a ptrace_stop being called with a pending fatal signal. Previously it would have been handled by schedule simply failing to sleep. As TASK_WAKEKILL is no longer part of TASK_TRACED schedule will sleep with a fatal_signal_pending. The code in signal_wake_up guarantees that the code will be awaked by any fatal signal that codes after TASK_TRACED is set. Previously the __state value of __TASK_TRACED was changed to TASK_RUNNING when woken up or back to TASK_TRACED when the code was left in ptrace_stop. Now when woken up ptrace_stop now clears JOBCTL_PTRACE_FROZEN and when left sleeping ptrace_unfreezed_traced clears JOBCTL_PTRACE_FROZEN. Tested-by: Kees Cook Reviewed-by: Oleg Nesterov Link: https://lkml.kernel.org/r/20220505182645.497868-10-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman"

task_work: allow TWA_SIGNAL without a rescheduling IPI

2022-04-30T14:39:32Z

Some use cases don't always need an IPI when sending a TWA_SIGNAL notification. Add TWA_SIGNAL_NO_IPI, which is just like TWA_SIGNAL, except it doesn't send an IPI to the target task. It merely sets TIF_NOTIFY_SIGNAL and wakes up the task. This can be useful in avoiding a forceful transition to the kernel if the task is running in userspace. Depending on the task_work in question, it may be quite fine waiting for the next reschedule or kernel enter anyway, or the use case may even have other mechanisms for hinting to the task that a transition may be useful. This can drive more cooperative scheduling of task_work. Reviewed-by: Pavel Begunkov Link: https://lore.kernel.org/r/821f42b6-7d91-8074-8212-d34998097de4@kernel.dk Signed-off-by: Jens Axboe

signal: Deliver SIGTRAP on perf event asynchronously if blocked

2022-04-22T10:14:05Z

With SIGTRAP on perf events, we have encountered termination of processes due to user space attempting to block delivery of SIGTRAP. Consider this case: ... sigset_t s; sigemptyset(&s); sigaddset(&s, SIGTRAP | ); sigprocmask(SIG_BLOCK, &s, ...); ... When the perf event triggers, while SIGTRAP is blocked, force_sig_perf() will force the signal, but revert back to the default handler, thus terminating the task. This makes sense for error conditions, but not so much for explicitly requested monitoring. However, the expectation is still that signals generated by perf events are synchronous, which will no longer be the case if the signal is blocked and delivered later. To give user space the ability to clearly distinguish synchronous from asynchronous signals, introduce siginfo_t::si_perf_flags and TRAP_PERF_FLAG_ASYNC (opted for flags in case more binary information is required in future). The resolution to the problem is then to (a) no longer force the signal (avoiding the terminations), but (b) tell user space via si_perf_flags if the signal was synchronous or not, so that such signals can be handled differently (e.g. let user space decide to ignore or consider the data imprecise). The alternative of making the kernel ignore SIGTRAP on perf events if the signal is blocked may work for some usecases, but likely causes issues in others that then have to revert back to interception of sigprocmask() (which we want to avoid). [ A concrete example: when using breakpoint perf events to track data-flow, in a region of code where signals are blocked, data-flow can no longer be tracked accurately. When a relevant asynchronous signal is received after unblocking the signal, the data-flow tracking logic needs to know its state is imprecise. ] Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events") Reported-by: Dmitry Vyukov Signed-off-by: Marco Elver Signed-off-by: Peter Zijlstra (Intel) Acked-by: Geert Uytterhoeven Tested-by: Dmitry Vyukov Link: https://lore.kernel.org/r/20220404111204.935357-1-elver@google.com

signal: Move set_notify_signal and clear_notify_signal into sched/signal.h

2022-03-10T22:51:50Z

The header tracehook.h is no place for code to live. The functions set_notify_signal and clear_notify_signal are not about signals. They are about interruptions that act like signals. The fundamental signal primitives wind up calling set_notify_signal and clear_notify_signal. Which means they need to be maintained with the signal code. Since set_notify_signal and clear_notify_signal must be maintained with the signal subsystem move them into sched/signal.h and claim them as part of the signal subsystem. Reviewed-by: Kees Cook Link: https://lkml.kernel.org/r/20220309162454.123006-10-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman"

signal: Remove the helper signal_group_exit

2022-01-08T18:43:57Z

This helper is misleading. It tests for an ongoing exec as well as the process having received a fatal signal. Sometimes it is appropriate to treat an on-going exec differently than a process that is shutting down due to a fatal signal. In particular taking the fast path out of exit_signals instead of retargeting signals is not appropriate during exec, and not changing the the exit code in do_group_exit during exec. Removing the helper makes it more obvious what is going on as both cases must be coded for explicitly. While removing the helper fix the two cases where I have observed using signal_group_exit resulted in the wrong result. In exit_signals only test for SIGNAL_GROUP_EXIT so that signals are retargetted during an exec. In do_group_exit use 0 as the exit code during an exec as de_thread does not set group_exit_code. As best as I can determine group_exit_code has been is set to 0 most of the time during de_thread. During a thread group stop group_exit_code is set to the stop signal and when the thread group receives SIGCONT group_exit_code is reset to 0. Link: https://lkml.kernel.org/r/20211213225350.27481-8-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman"