linux-toradex.git/kernel/entry, branch v5.16-rc6

signal: Replace force_fatal_sig with force_exit_sig when in doubt

2021-11-19T15:15:58+00:00

Recently to prevent issues with SECCOMP_RET_KILL and similar signals
being changed before they are delivered SA_IMMUTABLE was added.

Unfortunately this broke debuggers[1][2] which reasonably expect
to be able to trap synchronous SIGTRAP and SIGSEGV even when
the target process is not configured to handle those signals.

Add force_exit_sig and use it instead of force_fatal_sig where
historically the code has directly called do_exit.  This has the
implementation benefits of going through the signal exit path
(including generating core dumps) without the danger of allowing
userspace to ignore or change these signals.

This avoids userspace regressions as older kernels exited with do_exit
which debuggers also can not intercept.

In the future is should be possible to improve the quality of
implementation of the kernel by changing some of these force_exit_sig
calls to force_fatal_sig.  That can be done where it matters on
a case-by-case basis with careful analysis.

Reported-by: Kyle Huey 
Reported-by: kernel test robot 
[1] https://lkml.kernel.org/r/CAP045AoMY4xf8aC_4QU_-j7obuEPYgTcnQQP3Yxk=2X90jtpjw@mail.gmail.com
[2] https://lkml.kernel.org/r/20211117150258.GB5403@xsang-OptiPlex-9020
Fixes: 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed")
Fixes: a3616a3c0272 ("signal/m68k: Use force_sigsegv(SIGSEGV) in fpsp040_die")
Fixes: 83a1f27ad773 ("signal/powerpc: On swapcontext failure force SIGSEGV")
Fixes: 9bc508cf0791 ("signal/s390: Use force_sigsegv in default_trap_handler")
Fixes: 086ec444f866 ("signal/sparc32: In setup_rt_frame and setup_fram use force_fatal_sig")
Fixes: c317d306d550 ("signal/sparc32: Exit with a fatal signal when try_to_clear_window_buffer fails")
Fixes: 695dd0d634df ("signal/x86: In emulate_vsyscall force a signal instead of calling do_exit")
Fixes: 1fbd60df8a85 ("signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.")
Fixes: 941edc5bf174 ("exit/syscall_user_dispatch: Send ordinary signals on failure")
Link: https://lkml.kernel.org/r/871r3dqfv8.fsf_-_@email.froward.int.ebiederm.org
Reviewed-by: Kees Cook 
Tested-by: Kees Cook 
Tested-by: Kyle Huey 
Signed-off-by: "Eric W. Biederman"

Merge branch 'exit-cleanups-for-v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2021-11-11T00:15:54+00:00

Pull exit cleanups from Eric Biederman:
 "While looking at some issues related to the exit path in the kernel I
  found several instances where the code is not using the existing
  abstractions properly.

  This set of changes introduces force_fatal_sig a way of sending a
  signal and not allowing it to be caught, and corrects the misuse of
  the existing abstractions that I found.

  A lot of the misuse of the existing abstractions are silly things such
  as doing something after calling a no return function, rolling BUG by
  hand, doing more work than necessary to terminate a kernel thread, or
  calling do_exit(SIGKILL) instead of calling force_sig(SIGKILL).

  In the review a deficiency in force_fatal_sig and force_sig_seccomp
  where ptrace or sigaction could prevent the delivery of the signal was
  found. I have added a change that adds SA_IMMUTABLE to change that
  makes it impossible to interrupt the delivery of those signals, and
  allows backporting to fix force_sig_seccomp

  And Arnd found an issue where a function passed to kthread_run had the
  wrong prototype, and after my cleanup was failing to build."

* 'exit-cleanups-for-v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (23 commits)
  soc: ti: fix wkup_m3_rproc_boot_thread return type
  signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed
  signal: Replace force_sigsegv(SIGSEGV) with force_fatal_sig(SIGSEGV)
  exit/r8188eu: Replace the macro thread_exit with a simple return 0
  exit/rtl8712: Replace the macro thread_exit with a simple return 0
  exit/rtl8723bs: Replace the macro thread_exit with a simple return 0
  signal/x86: In emulate_vsyscall force a signal instead of calling do_exit
  signal/sparc32: In setup_rt_frame and setup_fram use force_fatal_sig
  signal/sparc32: Exit with a fatal signal when try_to_clear_window_buffer fails
  exit/syscall_user_dispatch: Send ordinary signals on failure
  signal: Implement force_fatal_sig
  exit/kthread: Have kernel threads return instead of calling do_exit
  signal/s390: Use force_sigsegv in default_trap_handler
  signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.
  signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON
  signal/sparc: In setup_tsb_params convert open coded BUG into BUG
  signal/powerpc: On swapcontext failure force SIGSEGV
  signal/sh: Use force_sig(SIGKILL) instead of do_group_exit(SIGKILL)
  signal/mips: Update (_save|_restore)_fp_context to fail with -EFAULT
  signal/sparc32: Remove unreachable do_exit in do_sparc_fault
  ...

exit/syscall_user_dispatch: Send ordinary signals on failure

2021-10-29T19:31:33+00:00

Use force_fatal_sig instead of calling do_exit directly.  This ensures
the ordinary signal handling path gets invoked, core dumps as
appropriate get created, and for multi-threaded processes all of the
threads are terminated not just a single thread.

When asked Gabriel Krisman Bertazi  said [1]:
> ebiederm@xmission.com (Eric W. Biederman) asked:
>
> > Why does do_syscal_user_dispatch call do_exit(SIGSEGV) and
> > do_exit(SIGSYS) instead of force_sig(SIGSEGV) and force_sig(SIGSYS)?
> >
> > Looking at the code these cases are not expected to happen, so I would
> > be surprised if userspace depends on any particular behaviour on the
> > failure path so I think we can change this.
>
> Hi Eric,
>
> There is not really a good reason, and the use case that originated the
> feature doesn't rely on it.
>
> Unless I'm missing yet another problem and others correct me, I think
> it makes sense to change it as you described.
>
> > Is using do_exit in this way something you copied from seccomp?
>
> I'm not sure, its been a while, but I think it might be just that.  The
> first prototype of SUD was implemented as a seccomp mode.

If at some point it becomes interesting we could relax
"force_fatal_sig(SIGSEGV)" to instead say
"force_sig_fault(SIGSEGV, SEGV_MAPERR, sd->selector)".

I avoid doing that in this patch to avoid making it possible
to catch currently uncatchable signals.

Cc: Gabriel Krisman Bertazi 
Cc: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Andy Lutomirski 
[1] https://lkml.kernel.org/r/87mtr6gdvi.fsf@collabora.com
Link: https://lkml.kernel.org/r/20211020174406.17889-14-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman

entry: rseq: Call rseq_handle_notify_resume() in tracehook_notify_resume()

2021-09-22T14:24:01+00:00

Invoke rseq_handle_notify_resume() from tracehook_notify_resume() now
that the two function are always called back-to-back by architectures
that have rseq.  The rseq helper is stubbed out for architectures that
don't support rseq, i.e. this is a nop across the board.

Note, tracehook_notify_resume() is horribly named and arguably does not
belong in tracehook.h as literally every line of code in it has nothing
to do with tracing.  But, that's been true since commit a42c6ded827d
("move key_repace_session_keyring() into tracehook_notify_resume()")
first usurped tracehook_notify_resume() back in 2012.  Punt cleaning that
mess up to future patches.

No functional change intended.

Acked-by: Mathieu Desnoyers 
Signed-off-by: Sean Christopherson 
Message-Id: <20210901203030.1292304-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini

KVM: rseq: Update rseq when processing NOTIFY_RESUME on xfer to KVM guest

2021-09-22T14:24:01+00:00

Invoke rseq's NOTIFY_RESUME handler when processing the flag prior to
transferring to a KVM guest, which is roughly equivalent to an exit to
userspace and processes many of the same pending actions.  While the task
cannot be in an rseq critical section as the KVM path is reachable only
by via ioctl(KVM_RUN), the side effects that apply to rseq outside of a
critical section still apply, e.g. the current CPU needs to be updated if
the task is migrated.

Clearing TIF_NOTIFY_RESUME without informing rseq can lead to segfaults
and other badness in userspace VMMs that use rseq in combination with KVM,
e.g. due to the CPU ID being stale after task migration.

Fixes: 72c3c0fe54a3 ("x86/kvm: Use generic xfer to guest work function")
Reported-by: Peter Foley 
Bisected-by: Doug Evans 
Acked-by: Mathieu Desnoyers 
Cc: Shakeel Butt 
Cc: Thomas Gleixner 
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson 
Message-Id: <20210901203030.1292304-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini

tick/nohz: Only check for RCU deferred wakeup on user/guest entry when needed

2021-05-31T08:14:49+00:00

Checking for and processing RCU-nocb deferred wakeup upon user/guest
entry is only relevant when nohz_full runs on the local CPU, otherwise
the periodic tick should take care of it.

Make sure we don't needlessly pollute these fast-paths as a -3%
performance regression on a will-it-scale.per_process_ops has been
reported so far.

Fixes: 47b8ff194c1f (entry: Explicitly flush pending rcuog wakeup before last rescheduling point)
Fixes: 4ae7dc97f726 (entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point)
Reported-by: kernel test robot 
Signed-off-by: Frederic Weisbecker 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Paul E. McKenney 
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210527113441.465489-1-frederic@kernel.org

Merge tag 'core-entry-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-04-26T16:41:15+00:00

Pull core entry updates from Thomas Gleixner:
 "A trivial cleanup of typo fixes"

* tag 'core-entry-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  entry: Fix typos in comments

preempt/dynamic: Fix typo in macro conditional statement

2021-04-19T18:02:57+00:00

Commit 40607ee97e4e ("preempt/dynamic: Provide irqentry_exit_cond_resched()
static call") tried to provide irqentry_exit_cond_resched() static call
in irqentry_exit, but has a typo in macro conditional statement.

Fixes: 40607ee97e4e ("preempt/dynamic: Provide irqentry_exit_cond_resched() static call")
Signed-off-by: Zhouyi Zhou 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20210410073523.5493-1-zhouzhouyi@gmail.com

entry: Fix typos in comments

2021-03-22T02:57:39+00:00

Fix 3 single-word typos in the generic syscall entry code.

Signed-off-by: Ingo Molnar 
Cc: Borislav Petkov 
Cc: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

entry: Explicitly flush pending rcuog wakeup before last rescheduling point

2021-02-17T13:12:43+00:00

Following the idle loop model, cleanly check for pending rcuog wakeup
before the last rescheduling point on resuming to user mode. This
way we can avoid to do it from rcu_user_enter() with the last resort
self-IPI hack that enforces rescheduling.

Signed-off-by: Frederic Weisbecker 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210131230548.32970-5-frederic@kernel.org