Factor out force_sig_seccomp from the seccomp signal generation and
place it in kernel/signal.c.  The function force_sig_seccomp takes a
parameter force_coredump to indicate that the sigaction field should
be reset to SIGDFL so that a coredump will be generated when the
signal is delivered.

force_sig_seccomp is then used to replace both seccomp_send_sigsys
and seccomp_init_siginfo.

force_sig_info_to_task gains an extra parameter to force using
the default signal action.

With this change seccomp is no longer a special case and there
becomes exactly one place do_coredump is called from.

Further it no longer becomes necessary for __seccomp_filter
to call do_group_exit.
Acked-by: NKees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/87r1gr6qc4.fsf_-_@disp2133Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

Starting the process wide cputime counter needs to be done in the same
sighand locking sequence than actually arming the related timer otherwise
this races against concurrent timers setting/expiring in the same
threadgroup.

Detecting that the cputime counter is started without holding the sighand
lock is a first step toward debugging such situations.
Suggested-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210726125513.271824-2-frederic@kernel.org

Now that __ARCH_SI_TRAPNO is no longer set by any architecture remove
all of the code it enabled from the kernel.

On alpha and sparc a more explict approach of using
send_sig_fault_trapno or force_sig_fault_trapno in the very limited
circumstances where si_trapno was set to a non-zero value.

The generic support that is being removed always set si_trapno on all
fault signals.  With only SIGILL ILL_ILLTRAP on sparc and SIGFPE and
SIGTRAP TRAP_UNK on alpla providing si_trapno values asking all senders
of fault signals to provide an si_trapno value does not make sense.

Making si_trapno an ordinary extension of the fault siginfo layout has
enabled the architecture generic implementation of SIGTRAP TRAP_PERF,
and enables other faulting signals to grow architecture generic
senders as well.

v1: https://lkml.kernel.org/r/m18s4zs7nu.fsf_-_@fess.ebiederm.org
v2: https://lkml.kernel.org/r/20210505141101.11519-8-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/87bl73xx6x.fsf_-_@disp2133Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

While reviewing the signal handlers on alpha it became clear that
si_trapno is only set to a non-zero value when sending SIGFPE and when
sending SITGRAP with si_code TRAP_UNK.

Add send_sig_fault_trapno and send SIGTRAP TRAP_UNK, and SIGFPE with it.

Remove the define of __ARCH_SI_TRAPNO and remove the always zero
si_trapno parameter from send_sig_fault and force_sig_fault.

v1: https://lkml.kernel.org/r/m1eeers7q7.fsf_-_@fess.ebiederm.org
v2: https://lkml.kernel.org/r/20210505141101.11519-7-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/87h7gvxx7l.fsf_-_@disp2133Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

While reviewing the signal handlers on sparc it became clear that
si_trapno is only set to a non-zero value when sending SIGILL with
si_code ILL_ILLTRP.

Add force_sig_fault_trapno and send SIGILL ILL_ILLTRP with it.

Remove the define of __ARCH_SI_TRAPNO and remove the always zero
si_trapno parameter from send_sig_fault and force_sig_fault.

v1: https://lkml.kernel.org/r/m1eeers7q7.fsf_-_@fess.ebiederm.org
v2: https://lkml.kernel.org/r/20210505141101.11519-7-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/87mtqnxx89.fsf_-_@disp2133Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

Change the type and name of task_struct::state. Drop the volatile and
shrink it to an 'unsigned int'. Rename it in order to find all uses
such that we can use READ_ONCE/WRITE_ONCE as appropriate.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NDaniel Bristot de Oliveira <bristot@redhat.com>
Acked-by: NWill Deacon <will@kernel.org>
Acked-by: NDaniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20210611082838.550736351@infradead.org

The kernel pushes context on to the userspace stack to prepare for the
user's signal handler. When the user has supplied an alternate signal
stack, via sigaltstack(2), it is easy for the kernel to verify that the
stack size is sufficient for the current hardware context.

Check if writing the hardware context to the alternate stack will exceed
it's size. If yes, then instead of corrupting user-data and proceeding with
the original signal handler, an immediate SIGSEGV signal is delivered.

Refactor the stack pointer check code from on_sig_stack() and use the new
helper.

While the kernel allows new source code to discover and use a sufficient
alternate signal stack size, this check is still necessary to protect
binaries with insufficient alternate signal stack size from data
corruption.

Fixes: c2bc11f1 ("x86, AVX-512: Enable AVX-512 States Context Switch")
Reported-by: NFlorian Weimer <fweimer@redhat.com>
Suggested-by: NJann Horn <jannh@google.com>
Suggested-by: NAndy Lutomirski <luto@kernel.org>
Signed-off-by: NChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Reviewed-by: NLen Brown <len.brown@intel.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20210518200320.17239-6-chang.seok.bae@intel.com
Link: https://bugzilla.kernel.org/show_bug.cgi?id=153531

Separate filling in siginfo for TRAP_PERF from deciding that
siginal needs to be sent.

There are enough little details that need to be correct when
properly filling in siginfo_t that it is easy to make mistakes
if filling in the siginfo_t is in the same function with other
logic.  So factor out force_sig_perf to reduce the cognative
load of on reviewers, maintainers and implementors.

v1: https://lkml.kernel.org/r/m17dkjqqxz.fsf_-_@fess.ebiederm.org
v2: https://lkml.kernel.org/r/20210505141101.11519-10-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/20210517195748.8880-3-ebiederm@xmission.comReviewed-by: NMarco Elver <elver@google.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

It's available everywhere now, no need to check or add dummy defines.
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Recently syzbot reported[0] that there is a deadlock amongst the users
of exec_update_mutex.  The problematic lock ordering found by lockdep
was:

   perf_event_open  (exec_update_mutex -> ovl_i_mutex)
   chown            (ovl_i_mutex       -> sb_writes)
   sendfile         (sb_writes         -> p->lock)
     by reading from a proc file and writing to overlayfs
   proc_pid_syscall (p->lock           -> exec_update_mutex)

While looking at possible solutions it occured to me that all of the
users and possible users involved only wanted to state of the given
process to remain the same.  They are all readers.  The only writer is
exec.

There is no reason for readers to block on each other.  So fix
this deadlock by transforming exec_update_mutex into a rw_semaphore
named exec_update_lock that only exec takes for writing.

Cc: Jann Horn <jannh@google.com>
Cc: Vasiliy Kulikov <segoon@openwall.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Christopher Yeoh <cyeoh@au1.ibm.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Fixes: eea96732 ("exec: Add exec_update_mutex to replace cred_guard_mutex")
[0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com
Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com
Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.orgSigned-off-by: NEric W. Biederman <ebiederm@xmission.com>

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: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NOleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20201026203230.386348-3-axboe@kernel.dk

This is in preparation for maintaining signal_pending() as the decider of
whether or not a schedule() loop should be broken, or continue sleeping.
This is different than the core signal use cases, which really need to know
whether an actual signal is pending or not. task_sigpending() returns
non-zero if TIF_SIGPENDING is set.

Only core kernel use cases should care about the distinction between
the two, make sure those use the task_sigpending() helper.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NOleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20201026203230.386348-2-axboe@kernel.dk

Create an independent helper thread_group_exited which returns true
when all threads have passed exit_notify in do_exit.  AKA all of the
threads are at least zombies and might be dead or completely gone.

Create this helper by taking the logic out of pidfd_poll where it is
already tested, and adding a READ_ONCE on the read of
task->exit_state.

I will be changing the user mode driver code to use this same logic
to know when a user mode driver needs to be restarted.

Place the new helper thread_group_exited in kernel/exit.c and
EXPORT it so it can be used by modules.

Link: https://lkml.kernel.org/r/20200702164140.4468-13-ebiederm@xmission.comAcked-by: NChristian Brauner <christian.brauner@ubuntu.com>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Tested-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

After the introduction of exchange_tids has_group_leader_pid is
equivalent to thread_group_leader.  After the last couple of cleanups
has_group_leader_pid has no more callers.

So remove the now unused and redundant has_group_leader_pid.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

The idea comes from the upstream discussion between Linus and Andrea:

  https://lore.kernel.org/lkml/20171102193644.GB22686@redhat.com/

A summary to the issue: there was a special path in handle_userfault() in
the past that we'll return a VM_FAULT_NOPAGE when we detected non-fatal
signals when waiting for userfault handling.  We did that by reacquiring
the mmap_sem before returning.  However that brings a risk in that the
vmas might have changed when we retake the mmap_sem and even we could be
holding an invalid vma structure.

This patch is a preparation of removing that special path by allowing the
page fault to return even faster if we were interrupted by a non-fatal
signal during a user-mode page fault handling routine.
Suggested-by: NLinus Torvalds <torvalds@linux-foundation.org>
Suggested-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Tested-by: NBrian Geffon <bgeffon@google.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Link: http://lkml.kernel.org/r/20200220160230.9598-1-peterx@redhat.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

For most architectures, we've got a quick path to detect fatal signal
after a handle_mm_fault().  Introduce a helper for that quick path.

It cleans the current codes a bit so we don't need to duplicate the same
check across archs.  More importantly, this will be an unified place that
we handle the signal immediately right after an interrupted page fault, so
it'll be much easier for us if we want to change the behavior of handling
signals later on for all the archs.

Note that currently only part of the archs are using this new helper,
because some archs have their own way to handle signals.  In the follow up
patches, we'll try to apply this helper to all the rest of archs.

Another note is that the "regs" parameter in the new helper is not used
yet.  It'll be used very soon.  Now we kept it in this patch only to avoid
touching all the archs again in the follow up patches.

[peterx@redhat.com: fix sparse warnings]
  Link: http://lkml.kernel.org/r/20200311145921.GD479302@xz-x1Signed-off-by: NPeter Xu <peterx@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Tested-by: NBrian Geffon <bgeffon@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Link: http://lkml.kernel.org/r/20200220155353.8676-4-peterx@redhat.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The cred_guard_mutex is problematic as it is held over possibly
indefinite waits for userspace.  The possible indefinite waits for
userspace that I have identified are: The cred_guard_mutex is held in
PTRACE_EVENT_EXIT waiting for the tracer.  The cred_guard_mutex is
held over "put_user(0, tsk->clear_child_tid)" in exit_mm().  The
cred_guard_mutex is held over "get_user(futex_offset, ...")  in
exit_robust_list.  The cred_guard_mutex held over copy_strings.

The functions get_user and put_user can trigger a page fault which can
potentially wait indefinitely in the case of userfaultfd or if
userspace implements part of the page fault path.

In any of those cases the userspace process that the kernel is waiting
for might make a different system call that winds up taking the
cred_guard_mutex and result in deadlock.

Holding a mutex over any of those possibly indefinite waits for
userspace does not appear necessary.  Add exec_update_mutex that will
just cover updating the process during exec where the permissions and
the objects pointed to by the task struct may be out of sync.

The plan is to switch the users of cred_guard_mutex to
exec_update_mutex one by one.  This lets us move forward while still
being careful and not introducing any regressions.

Link: https://lore.kernel.org/lkml/20160921152946.GA24210@dhcp22.suse.cz/
Link: https://lore.kernel.org/lkml/AM6PR03MB5170B06F3A2B75EFB98D071AE4E60@AM6PR03MB5170.eurprd03.prod.outlook.com/
Link: https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@redhat.com/
Link: https://lore.kernel.org/lkml/20160923095031.GA14923@redhat.com/
Link: https://lore.kernel.org/lkml/20170213141452.GA30203@redhat.com/
Ref: 45c1a159b85b ("Add PTRACE_O_TRACEVFORKDONE and PTRACE_O_TRACEEXIT facilities.")
Ref: 456f17cd1a28 ("[PATCH] user-vm-unlock-2.5.31-A2")
Reviewed-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NBernd Edlinger <bernd.edlinger@hotmail.de>
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>

Put it where it belongs and clean up the ifdeffery in fork completely.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190821192922.743229404@linutronix.de

The expiry cache belongs into the posix_cputimers container where the other
cpu timers information is.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NFrederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190821192921.014444012@linutronix.de

Per task/process data of posix CPU timers is all over the place which
makes the code hard to follow and requires ifdeffery.

Create a container to hold all this information in one place, so data is
consolidated and the ifdeffery can be confined to the posix timer header
file and removed from places like fork.

As a first step, move the cpu_timers list head array into the new struct
and clean up the initializers and simplify fork. The remaining #ifdef in
fork will be removed later.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NFrederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190821192920.819418976@linutronix.de

task->saved_sigmask and ->restore_sigmask are only used in the ret-from-
syscall paths.  This means that set_user_sigmask() can save ->blocked in
->saved_sigmask and do set_restore_sigmask() to indicate that ->blocked
was modified.

This way the callers do not need 2 sigset_t's passed to set/restore and
restore_user_sigmask() renamed to restore_saved_sigmask_unless() turns
into the trivial helper which just calls restore_saved_sigmask().

Link: http://lkml.kernel.org/r/20190606113206.GA9464@redhat.comSigned-off-by: NOleg Nesterov <oleg@redhat.com>
Cc: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Eric Wong <e@80x24.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: David Laight <David.Laight@aculab.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

struct sighand_struct::siglock field is the most used field by far, put
it first so that is can be accessed without IMM8 or IMM32 encoding on
x86_64.

Space savings (on trimmed down VM test config):

add/remove: 0/0 grow/shrink: 8/68 up/down: 49/-1147 (-1098)
Function                                     old     new   delta
complete_signal                              512     533     +21
do_signalfd4                                 335     346     +11
__cleanup_sighand                             39      43      +4
unhandled_signal                              49      52      +3
prepare_signal                               692     695      +3
ignore_signals                                37      40      +3
__tty_check_change.part                      248     251      +3
ksys_unshare                                 780     781      +1
sighand_ctor                                  33      29      -4
ptrace_trap_notify                            60      56      -4
sigqueue_free                                 98      91      -7
run_posix_cpu_timers                        1389    1382      -7
proc_pid_status                             2448    2441      -7
proc_pid_limits                              344     337      -7
posix_cpu_timer_rearm                        222     215      -7
posix_cpu_timer_get                          249     242      -7
kill_pid_info_as_cred                        243     236      -7
freeze_task                                  197     190      -7
flush_old_exec                              1873    1866      -7
do_task_stat                                3363    3356      -7
do_send_sig_info                              98      91      -7
do_group_exit                                147     140      -7
init_sighand                                2088    2080      -8
do_notify_parent_cldstop                     399     391      -8
signalfd_cleanup                              50      41      -9
do_notify_parent                             557     545     -12
__send_signal                               1029    1017     -12
ptrace_stop                                  590     577     -13
get_signal                                  1576    1563     -13
__lock_task_sighand                          112      99     -13
zap_pid_ns_processes                         391     377     -14
update_rlimit_cpu                             78      64     -14
tty_signal_session_leader                    413     399     -14
tty_open_proc_set_tty                        149     135     -14
tty_jobctrl_ioctl                            936     922     -14
set_cpu_itimer                               339     325     -14
ptrace_resume                                226     212     -14
ptrace_notify                                110      96     -14
proc_clear_tty                                81      67     -14
posix_cpu_timer_del                          229     215     -14
kernel_sigaction                             156     142     -14
getrusage                                    977     963     -14
get_current_tty                               98      84     -14
force_sigsegv                                 89      75     -14
force_sig_info                               205     191     -14
flush_signals                                 83      69     -14
flush_itimer_signals                          85      71     -14
do_timer_create                             1120    1106     -14
do_sigpending                                 88      74     -14
do_signal_stop                               537     523     -14
cgroup_init_fs_context                       644     630     -14
call_usermodehelper_exec_async               402     388     -14
calculate_sigpending                          58      44     -14
__x64_sys_timer_delete                       248     234     -14
__set_current_blocked                         80      66     -14
__ptrace_unlink                              310     296     -14
__ptrace_detach.part                         187     173     -14
send_sigqueue                                362     347     -15
get_cpu_itimer                               214     199     -15
signalfd_poll                                175     159     -16
dequeue_signal                               340     323     -17
do_getitimer                                 192     174     -18
release_task.part                           1060    1040     -20
ptrace_peek_siginfo                          408     387     -21
posix_cpu_timer_set                          827     806     -21
exit_signals                                 437     416     -21
do_sigaction                                 541     520     -21
do_setitimer                                 485     464     -21
disassociate_ctty.part                       545     517     -28
__x64_sys_rt_sigtimedwait                    721     679     -42
__x64_sys_ptrace                            1319    1277     -42
ptrace_request                              1828    1782     -46
signalfd_read                                507     459     -48
wait_consider_task                          2027    1971     -56
do_coredump                                 3672    3616     -56
copy_process.part                           6936    6871     -65

Link: http://lkml.kernel.org/r/20190503192800.GA18004@avx2Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

force_sig_info always delivers to the current task and the signal
parameter always matches info.si_signo.  So remove those parameters to
make it a simpler less error prone interface, and to make it clear
that none of the callers are doing anything clever.

This guarantees that force_sig_info will not grow any new buggy
callers that attempt to call force_sig on a non-current task, or that
pass an signal number that does not match info.si_signo.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

As synchronous exceptions really only make sense against the current
task (otherwise how are you synchronous) remove the task parameter
from from force_sig_fault to make it explicit that is what is going
on.

The two known exceptions that deliver a synchronous exception to a
stopped ptraced task have already been changed to
force_sig_fault_to_task.

The callers have been changed with the following emacs regular expression
(with obvious variations on the architectures that take more arguments)
to avoid typos:

force_sig_fault[(]\([^,]+\)[,]\([^,]+\)[,]\([^,]+\)[,]\W+current[)]
->
force_sig_fault(\1,\2,\3)
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

In preparation for removing the task parameter from force_sig_fault
introduce force_sig_fault_to_task and use it for the two cases where
it matters.

On mips force_fcr31_sig calls force_sig_fault and is called on either
the current task, or a task that is suspended and is being switched to
by the scheduler.  This is safe because the task being switched to by
the scheduler is guaranteed to be suspended.  This ensures that
task->sighand is stable while the signal is delivered to it.

On parisc user_enable_single_step calls force_sig_fault and is in turn
called by ptrace_request.  The function ptrace_request always calls
user_enable_single_step on a child that is stopped for tracing.  The
child being traced and not reaped ensures that child->sighand is not
NULL, and that the child will not change child->sighand.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

All of the callers pass current into force_sig_mceer so remove the
task parameter to make this obvious.

This also makes it clear that force_sig_mceerr passes current
into force_sig_info.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

All of the remaining callers pass current into force_sig so
remove the task parameter to make this obvious and to make
misuse more difficult in the future.

This also makes it clear force_sig passes current into force_sig_info.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

The function force_sigsegv is always called on the current task
so passing in current is redundant and not passing in current
makes this fact obvious.

This also makes it clear force_sigsegv always calls force_sig
on the current task.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

The usb support for asyncio encoded one of it's values in the wrong
field.  It should have used si_value but instead used si_addr which is
not present in the _rt union member of struct siginfo.

The practical result of this is that on a 64bit big endian kernel
when delivering a signal to a 32bit process the si_addr field
is set to NULL, instead of the expected pointer value.

This issue can not be fixed in copy_siginfo_to_user32 as the usb
usage of the the _sigfault (aka si_addr) member of the siginfo
union when SI_ASYNCIO is set is incompatible with the POSIX and
glibc usage of the _rt member of the siginfo union.

Therefore replace kill_pid_info_as_cred with kill_pid_usb_asyncio a
dedicated function for this one specific case.  There are no other
users of kill_pid_info_as_cred so this specialization should have no
impact on the amount of code in the kernel.  Have kill_pid_usb_asyncio
take instead of a siginfo_t which is difficult and error prone, 3
arguments, a signal number, an errno value, and an address enconded as
a sigval_t.  The encoding of the address as a sigval_t allows the
code that reads the userspace request for a signal to handle this
compat issue along with all of the other compat issues.

Add BUILD_BUG_ONs in kernel/signal.c to ensure that we can now place
the pointer value at the in si_pid (instead of si_addr).  That is the
code now verifies that si_pid and si_addr always occur at the same
location.  Further the code veries that for native structures a value
placed in si_pid and spilling into si_uid will appear in userspace in
si_addr (on a byte by byte copy of siginfo or a field by field copy of
siginfo).  The code also verifies that for a 64bit kernel and a 32bit
userspace the 32bit pointer will fit in si_pid.

I have used the usbsig.c program below written by Alan Stern and
slightly tweaked by me to run on a big endian machine to verify the
issue exists (on sparc64) and to confirm the patch below fixes the issue.

 /* usbsig.c -- test USB async signal delivery */

 #define _GNU_SOURCE
 #include <stdio.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <unistd.h>
 #include <endian.h>
 #include <linux/usb/ch9.h>
 #include <linux/usbdevice_fs.h>

 static struct usbdevfs_urb urb;
 static struct usbdevfs_disconnectsignal ds;
 static volatile sig_atomic_t done = 0;

 void urb_handler(int sig, siginfo_t *info , void *ucontext)
 {
 	printf("Got signal %d, signo %d errno %d code %d addr: %p urb: %p\n",
 	       sig, info->si_signo, info->si_errno, info->si_code,
 	       info->si_addr, &urb);

 	printf("%s\n", (info->si_addr == &urb) ? "Good" : "Bad");
 }

 void ds_handler(int sig, siginfo_t *info , void *ucontext)
 {
 	printf("Got signal %d, signo %d errno %d code %d addr: %p ds: %p\n",
 	       sig, info->si_signo, info->si_errno, info->si_code,
 	       info->si_addr, &ds);

 	printf("%s\n", (info->si_addr == &ds) ? "Good" : "Bad");
 	done = 1;
 }

 int main(int argc, char **argv)
 {
 	char *devfilename;
 	int fd;
 	int rc;
 	struct sigaction act;
 	struct usb_ctrlrequest *req;
 	void *ptr;
 	char buf[80];

 	if (argc != 2) {
 		fprintf(stderr, "Usage: usbsig device-file-name\n");
 		return 1;
 	}

 	devfilename = argv[1];
 	fd = open(devfilename, O_RDWR);
 	if (fd == -1) {
 		perror("Error opening device file");
 		return 1;
 	}

 	act.sa_sigaction = urb_handler;
 	sigemptyset(&act.sa_mask);
 	act.sa_flags = SA_SIGINFO;

 	rc = sigaction(SIGUSR1, &act, NULL);
 	if (rc == -1) {
 		perror("Error in sigaction");
 		return 1;
 	}

 	act.sa_sigaction = ds_handler;
 	sigemptyset(&act.sa_mask);
 	act.sa_flags = SA_SIGINFO;

 	rc = sigaction(SIGUSR2, &act, NULL);
 	if (rc == -1) {
 		perror("Error in sigaction");
 		return 1;
 	}

 	memset(&urb, 0, sizeof(urb));
 	urb.type = USBDEVFS_URB_TYPE_CONTROL;
 	urb.endpoint = USB_DIR_IN | 0;
 	urb.buffer = buf;
 	urb.buffer_length = sizeof(buf);
 	urb.signr = SIGUSR1;

 	req = (struct usb_ctrlrequest *) buf;
 	req->bRequestType = USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_DEVICE;
 	req->bRequest = USB_REQ_GET_DESCRIPTOR;
 	req->wValue = htole16(USB_DT_DEVICE << 8);
 	req->wIndex = htole16(0);
 	req->wLength = htole16(sizeof(buf) - sizeof(*req));

 	rc = ioctl(fd, USBDEVFS_SUBMITURB, &urb);
 	if (rc == -1) {
 		perror("Error in SUBMITURB ioctl");
 		return 1;
 	}

 	rc = ioctl(fd, USBDEVFS_REAPURB, &ptr);
 	if (rc == -1) {
 		perror("Error in REAPURB ioctl");
 		return 1;
 	}

 	memset(&ds, 0, sizeof(ds));
 	ds.signr = SIGUSR2;
 	ds.context = &ds;
 	rc = ioctl(fd, USBDEVFS_DISCSIGNAL, &ds);
 	if (rc == -1) {
 		perror("Error in DISCSIGNAL ioctl");
 		return 1;
 	}

 	printf("Waiting for usb disconnect\n");
 	while (!done) {
 		sleep(1);
 	}

 	close(fd);
 	return 0;
 }

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Oliver Neukum <oneukum@suse.com>
Fixes: v2.3.39
Cc: stable@vger.kernel.org
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

This file uses "task" 85 times and "tsk" 25 times.  It is better to be
consistent.

Link: http://lkml.kernel.org/r/20181129180547.15976-1-avagin@gmail.comSigned-off-by: NAndrei Vagin <avagin@gmail.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There are a few system calls (pselect, ppoll, etc) which replace a task
sigmask while they are running in a kernel-space

When a task calls one of these syscalls, the kernel saves a current
sigmask in task->saved_sigmask and sets a syscall sigmask.

On syscall-exit-stop, ptrace traps a task before restoring the
saved_sigmask, so PTRACE_GETSIGMASK returns the syscall sigmask and
PTRACE_SETSIGMASK does nothing, because its sigmask is replaced by
saved_sigmask, when the task returns to user-space.

This patch fixes this problem.  PTRACE_GETSIGMASK returns saved_sigmask
if it's set.  PTRACE_SETSIGMASK drops the TIF_RESTORE_SIGMASK flag.

Link: http://lkml.kernel.org/r/20181120060616.6043-1-avagin@gmail.com
Fixes: 29000cae ("ptrace: add ability to get/set signal-blocked mask")
Signed-off-by: NAndrei Vagin <avagin@gmail.com>
Acked-by: NOleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

atomic_t variables are currently used to implement reference
counters with the following properties:

 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable signal_struct.sigcnt is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

** Important note for maintainers:

Some functions from refcount_t API defined in lib/refcount.c
have different memory ordering guarantees than their atomic
counterparts.

The full comparison can be seen in
https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
in state to be merged to the documentation tree.

Normally the differences should not matter since refcount_t provides
enough guarantees to satisfy the refcounting use cases, but in
some rare cases it might matter.

Please double check that you don't have some undocumented
memory guarantees for this variable usage.

For the signal_struct.sigcnt it might make a difference
in following places:

 - put_signal_struct(): decrement in refcount_dec_and_test() only
   provides RELEASE ordering and control dependency on success
   vs. fully ordered atomic counterpart
Suggested-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NElena Reshetova <elena.reshetova@intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NDavid Windsor <dwindsor@gmail.com>
Reviewed-by: NHans Liljestrand <ishkamiel@gmail.com>
Reviewed-by: NAndrea Parri <andrea.parri@amarulasolutions.com>
Reviewed-by: NOleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: viro@zeniv.linux.org.uk
Link: https://lkml.kernel.org/r/1547814450-18902-3-git-send-email-elena.reshetova@intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

atomic_t variables are currently used to implement reference
counters with the following properties:

 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable sighand_struct.count is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

** Important note for maintainers:

Some functions from refcount_t API defined in lib/refcount.c
have different memory ordering guarantees than their atomic
counterparts.

The full comparison can be seen in
https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
in state to be merged to the documentation tree.

Normally the differences should not matter since refcount_t provides
enough guarantees to satisfy the refcounting use cases, but in
some rare cases it might matter.

Please double check that you don't have some undocumented
memory guarantees for this variable usage.

For the sighand_struct.count it might make a difference
in following places:

 - __cleanup_sighand: decrement in refcount_dec_and_test() only
   provides RELEASE ordering and control dependency on success
   vs. fully ordered atomic counterpart
Suggested-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NElena Reshetova <elena.reshetova@intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NDavid Windsor <dwindsor@gmail.com>
Reviewed-by: NHans Liljestrand <ishkamiel@gmail.com>
Reviewed-by: NAndrea Parri <andrea.parri@amarulasolutions.com>
Reviewed-by: NOleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: viro@zeniv.linux.org.uk
Link: https://lkml.kernel.org/r/1547814450-18902-2-git-send-email-elena.reshetova@intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Linus recently observed that if we did not worry about the padding
member in struct siginfo it is only about 48 bytes, and 48 bytes is
much nicer than 128 bytes for allocating on the stack and copying
around in the kernel.

The obvious thing of only adding the padding when userspace is
including siginfo.h won't work as there are sigframe definitions in
the kernel that embed struct siginfo.

So split siginfo in two; kernel_siginfo and siginfo.  Keeping the
traditional name for the userspace definition.  While the version that
is used internally to the kernel and ultimately will not be padded to
128 bytes is called kernel_siginfo.

The definition of struct kernel_siginfo I have put in include/signal_types.h

A set of buildtime checks has been added to verify the two structures have
the same field offsets.

To make it easy to verify the change kernel_siginfo retains the same
size as siginfo.  The reduction in size comes in a following change.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

There are no more users of SEND_SIG_FORCED so it may be safely removed.

Remove the definition of SEND_SIG_FORCED, it's use in is_si_special,
it's use in TP_STORE_SIGINFO, and it's use in __send_signal as without
any users the uses of SEND_SIG_FORCED are now unncessary.

This makes the code simpler, easier to understand and use.  Users of
signal sending functions now no longer need to ask themselves do I
need to use SEND_SIG_FORCED.
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

None of the callers use the it so remove it.
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

Patch series "signal: refactor some functions", v3.

This series refactors a bunch of functions in signal.c to simplify parts
of the code.

The greatest single change is declaring the static do_sigpending() helper
as void which makes it possible to remove a bunch of unnecessary checks in
the syscalls later on.

This patch (of 17):

force_sigsegv() returned 0 unconditionally so it doesn't make sense to have
it return at all. In addition, there are no callers that check
force_sigsegv()'s return value.

Link: http://lkml.kernel.org/r/20180602103653.18181-2-christian@brauner.ioSigned-off-by: NChristian Brauner <christian@brauner.io>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Morris <james.morris@microsoft.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Wen Yang <wen.yang99@zte.com.cn> and majiang <ma.jiang@zte.com.cn>
report that a periodic signal received during fork can cause fork to
continually restart preventing an application from making progress.

The code was being overly pessimistic.  Fork needs to guarantee that a
signal sent to multiple processes is logically delivered before the
fork and just to the forking process or logically delivered after the
fork to both the forking process and it's newly spawned child.  For
signals like periodic timers that are always delivered to a single
process fork can safely complete and let them appear to logically
delivered after the fork().

While examining this issue I also discovered that fork today will miss
signals delivered to multiple processes during the fork and handled by
another thread.  Similarly the current code will also miss blocked
signals that are delivered to multiple process, as those signals will
not appear pending during fork.

Add a list of each thread that is currently forking, and keep on that
list a signal set that records all of the signals sent to multiple
processes.  When fork completes initialize the new processes
shared_pending signal set with it.  The calculate_sigpending function
will see those signals and set TIF_SIGPENDING causing the new task to
take the slow path to userspace to handle those signals.  Making it
appear as if those signals were received immediately after the fork.

It is not possible to send real time signals to multiple processes and
exceptions don't go to multiple processes, which means that that are
no signals sent to multiple processes that require siginfo.  This
means it is safe to not bother collecting siginfo on signals sent
during fork.

The sigaction of a child of fork is initially the same as the
sigaction of the parent process.  So a signal the parent ignores the
child will also initially ignore.  Therefore it is safe to ignore
signals sent to multiple processes and ignored by the forking process.

Signals sent to only a single process or only a single thread and delivered
during fork are treated as if they are received after the fork, and generally
not dealt with.  They won't cause any problems.

V2: Added removal from the multiprocess list on failure.
V3: Use -ERESTARTNOINTR directly
V4: - Don't queue both SIGCONT and SIGSTOP
    - Initialize signal_struct.multiprocess in init_task
    - Move setting of shared_pending to before the new task
      is visible to signals.  This prevents signals from comming
      in before shared_pending.signal is set to delayed.signal
      and being lost.
V5: - rework list add and delete to account for idle threads
v6: - Use sigdelsetmask when removing stop signals

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=200447
Reported-by: Wen Yang <wen.yang99@zte.com.cn> and
Reported-by: Nmajiang <ma.jiang@zte.com.cn>
Fixes: 4a2c7a78 ("[PATCH] make fork() atomic wrt pgrp/session signals")
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

There are only two signals that are delivered to every member of a
signal group: SIGSTOP and SIGKILL.  Signal delivery requires every
signal appear to be delivered either before or after a clone syscall.
SIGKILL terminates the clone so does not need to be considered.  Which
leaves only SIGSTOP that needs to be considered when creating new
threads.

Today in the event of a group stop TIF_SIGPENDING will get set and the
fork will restart ensuring the fork syscall participates in the group
stop.

A fork (especially of a process with a lot of memory) is one of the
most expensive system so we really only want to restart a fork when
necessary.

It is easy so check to see if a SIGSTOP is ongoing and have the new
thread join it immediate after the clone completes.  Making it appear
the clone completed happened just before the SIGSTOP.

The calculate_sigpending function will see the bits set in jobctl and
set TIF_SIGPENDING to ensure the new task takes the slow path to userspace.

V2: The call to task_join_group_stop was moved before the new task is
    added to the thread group list.  This should not matter as
    sighand->siglock is held over both the addition of the threads,
    the call to task_join_group_stop and do_signal_stop.  But the change
    is trivial and it is one less thing to worry about when reading
    the code.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

Add a function calculate_sigpending to test to see if any signals are
pending for a new task immediately following fork.  Signals have to
happen either before or after fork.  Today our practice is to push
all of the signals to before the fork, but that has the downside that
frequent or periodic signals can make fork take much much longer than
normal or prevent fork from completing entirely.

So we need move signals that we can after the fork to prevent that.

This updates the code to set TIF_SIGPENDING on a new task if there
are signals or other activities that have moved so that they appear
to happen after the fork.

As the code today restarts if it sees any such activity this won't
immediately have an effect, as there will be no reason for it
to set TIF_SIGPENDING immediately after the fork.

Adding calculate_sigpending means the code in fork can safely be
changed to not always restart if a signal is pending.

The new calculate_sigpending function sets sigpending if there
are pending bits in jobctl, pending signals, the freezer needs
to freeze the new task or the live kernel patching framework
need the new thread to take the slow path to userspace.

I have verified that setting TIF_SIGPENDING does make a new process
take the slow path to userspace before it executes it's first userspace
instruction.

I have looked at the callers of signal_wake_up and the code paths
setting TIF_SIGPENDING and I don't see anything else that needs to be
handled.  The code probably doesn't need to set TIF_SIGPENDING for the
kernel live patching as it uses a separate thread flag as well.  But
at this point it seems safer reuse the recalc_sigpending logic and get
the kernel live patching folks to sort out their story later.

V2: I have moved the test into schedule_tail where siglock can
    be grabbed and recalc_sigpending can be reused directly.
    Further as the last action of setting up a new task this
    guarantees that TIF_SIGPENDING will be properly set in the
    new process.

    The helper calculate_sigpending takes the siglock and
    uncontitionally sets TIF_SIGPENDING and let's recalc_sigpending
    clear TIF_SIGPENDING if it is unnecessary.  This allows reusing
    the existing code and keeps maintenance of the conditions simple.

    Oleg Nesterov <oleg@redhat.com>  suggested the movement
    and pointed out the need to take siglock if this code
    was going to be called while the new task is discoverable.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>