linux.git/arch/s390/kernel/process.c, branch v5.14

s390/signal: switch to using vdso for sigreturn and syscall restart

2021-07-08T20:09:47+00:00

with generic entry, there's a bug when it comes to restarting of signals.
The failing sequence is:

a) a signal is coming in, and no handler is registered, so the lower
   part of arch_do_signal_or_restart() in arch/s390/kernel/signal.c
   sets PIF_SYSCALL_RESTART.

b) a second signal gets pending while the kernel is still in the exit
   loop, and for that one, a handler exists.

c) The first part of arch_do_signal_or_restart() is called. That part
   calls handle_signal(), which sets up stack + registers for handling
   the signal.

d) __do_syscall() in arch/s390/kernel/syscall.c checks for
   PIF_SYSCALL_RESTART right before leaving to userspace. If it is set,
   it restart's the syscall. However, the registers are already setup
   for handling a signal from c). The syscall is now restarted with the
   wrong arguments.

Change the code to:

- use vdso for syscall_restart() instead of PIF_SYSCALL_RESTART because
  we cannot rewind and go back to userspace on s390 because the system call
  number might be encoded in the svc instruction.
- for all other syscalls we rewind the PSW and return to userspace.

Cc:  # v5.12+ d57778feb987: s390/vdso: always enable vdso
Cc:  # v5.12+ 686341f2548b: s390/vdso64: add sigreturn,rt_sigreturn and restart_syscall
Cc:  # v5.12+ 43e1f76b0b69: s390/vdso: rename VDSO64_LBASE to VDSO_LBASE
Cc:  # v5.12+ 779df2248739: s390/vdso: add minimal compat vdso
Cc:  # v5.12+
Signed-off-by: Sven Schnelle 
Reviewed-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

sched: Introduce task_is_running()

2021-06-18T09:43:07+00:00

Replace a bunch of 'p->state == TASK_RUNNING' with a new helper:
task_is_running(p).

Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Davidlohr Bueso 
Acked-by: Geert Uytterhoeven 
Acked-by: Will Deacon 
Link: https://lore.kernel.org/r/20210611082838.222401495@infradead.org

arch: setup PF_IO_WORKER threads like PF_KTHREAD

2021-02-22T00:25:22+00:00

PF_IO_WORKER are kernel threads too, but they aren't PF_KTHREAD in the
sense that we don't assign ->set_child_tid with our own structure. Just
ensure that every arch sets up the PF_IO_WORKER threads like kthreads
in the arch implementation of copy_thread().

Signed-off-by: Jens Axboe

s390: convert to generic entry

2021-01-19T11:29:26+00:00

This patch converts s390 to use the generic entry infrastructure from
kernel/entry/*.

There are a few special things on s390:

- PIF_PER_TRAP is moved to TIF_PER_TRAP as the generic code doesn't
  know about our PIF flags in exit_to_user_mode_loop().

- The old code had several ways to restart syscalls:

  a) PIF_SYSCALL_RESTART, which was only set during execve to force a
     restart after upgrading a process (usually qemu-kvm) to pgste page
     table extensions.

  b) PIF_SYSCALL, which is set by do_signal() to indicate that the
     current syscall should be restarted. This is changed so that
     do_signal() now also uses PIF_SYSCALL_RESTART. Continuing to use
     PIF_SYSCALL doesn't work with the generic code, and changing it
     to PIF_SYSCALL_RESTART makes PIF_SYSCALL and PIF_SYSCALL_RESTART
     more unique.

- On s390 calling sys_sigreturn or sys_rt_sigreturn is implemented by
executing a svc instruction on the process stack which causes a fault.
While handling that fault the fault code sets PIF_SYSCALL to hand over
processing to the syscall code on exit to usermode.

The patch introduces PIF_SYSCALL_RET_SET, which is set if ptrace sets
a return value for a syscall. The s390x ptrace ABI uses r2 both for the
syscall number and return value, so ptrace cannot set the syscall number +
return value at the same time. The flag makes handling that a bit easier.
do_syscall() will just skip executing the syscall if PIF_SYSCALL_RET_SET
is set.

CONFIG_DEBUG_ASCE was removd in favour of the generic CONFIG_DEBUG_ENTRY.
CR1/7/13 will be checked both on kernel entry and exit to contain the
correct asces.

Signed-off-by: Sven Schnelle 
Signed-off-by: Vasily Gorbik

s390/mm: remove set_fs / rework address space handling

2020-11-23T11:01:12+00:00

Remove set_fs support from s390. With doing this rework address space
handling and simplify it. As a result address spaces are now setup
like this:

CPU running in              | %cr1 ASCE | %cr7 ASCE | %cr13 ASCE
----------------------------|-----------|-----------|-----------
user space                  |  user     |  user     |  kernel
kernel, normal execution    |  kernel   |  user     |  kernel
kernel, kvm guest execution |  gmap     |  user     |  kernel

To achieve this the getcpu vdso syscall is removed in order to avoid
secondary address mode and a separate vdso address space in for user
space. The getcpu vdso syscall will be implemented differently with a
subsequent patch.

The kernel accesses user space always via secondary address space.
This happens in different ways:
- with mvcos in home space mode and directly read/write to secondary
  address space
- with mvcs/mvcp in primary space mode and copy from primary space to
  secondary space or vice versa
- with e.g. cs in secondary space mode and access secondary space

Switching translation modes happens with sacf before and after
instructions which access user space, like before.

Lazy handling of control register reloading is removed in the hope to
make everything simpler, but at the cost of making kernel entry and
exit a bit slower. That is: on kernel entry the primary asce is always
changed to contain the kernel asce, and on kernel exit the primary
asce is changed again so it contains the user asce.

In kernel mode there is only one exception to the primary asce: when
kvm guests are executed the primary asce contains the gmap asce (which
describes the guest address space). The primary asce is reset to
kernel asce whenever kvm guest execution is interrupted, so that this
doesn't has to be taken into account for any user space accesses.

Reviewed-by: Sven Schnelle 
Signed-off-by: Heiko Carstens

Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2020-08-09T20:33:54+00:00

Pull regset conversion fix from Al Viro:
 "Fix a regression from an unnoticed bisect hazard in the regset series.

  A bunch of old (aout, originally) primitives used by coredumps became
  dead code after fdpic conversion to regsets. Removal of that dead code
  had been the first commit in the followups to regset series;
  unfortunately, it happened to hide the bisect hazard on sh (extern for
  fpregs_get() had not been updated in the main series when it should
  have been; followup simply made fpregs_get() static). And without that
  followup commit this bisect hazard became breakage in the mainline"

Tested-by: John Paul Adrian Glaubitz 

* 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  kill unused dump_fpu() instances

kill unused dump_fpu() instances

2020-07-27T18:33:10+00:00

dump_fpu() is used only on the architectures that support elf
and have neither CORE_DUMP_USE_REGSET nor ELF_CORE_COPY_FPREGS
defined.

Currently that's csky, m68k, microblaze, nds32 and unicore32.  The rest
of the instances are dead code.

NB: THIS MUST GO AFTER ELF_FDPIC CONVERSION

Signed-off-by: Al Viro

arch: rename copy_thread_tls() back to copy_thread()

2020-07-04T21:41:37+00:00

Now that HAVE_COPY_THREAD_TLS has been removed, rename copy_thread_tls()
back simply copy_thread(). It's a simpler name, and doesn't imply that only
tls is copied here. This finishes an outstanding chunk of internal process
creation work since we've added clone3().

Cc: linux-arch@vger.kernel.org
Acked-by: Thomas Bogendoerfer A
Acked-by: Stafford Horne 
Acked-by: Greentime Hu 
Acked-by: Geert Uytterhoeven A
Reviewed-by: Kees Cook 
Signed-off-by: Christian Brauner

s390: prevent leaking kernel address in BEAR

2020-03-10T14:16:25+00:00

When userspace executes a syscall or gets interrupted,
BEAR contains a kernel address when returning to userspace.
This make it pretty easy to figure out where the kernel is
mapped even with KASLR enabled. To fix this, add lpswe to
lowcore and always execute it there, so userspace sees only
the lowcore address of lpswe. For this we have to extend
both critical_cleanup and the SWITCH_ASYNC macro to also check
for lpswe addresses in lowcore.

Fixes: b2d24b97b2a9 ("s390/kernel: add support for kernel address space layout randomization (KASLR)")
Cc:  # v5.2+
Reviewed-by: Gerald Schaefer 
Signed-off-by: Sven Schnelle 
Signed-off-by: Vasily Gorbik

s390/process: avoid custom stack unwinding in get_wchan

2019-10-31T16:20:53+00:00

Currently get_wchan uses custom stack unwinding implementation which
relies on back_chain presence. Replace it with more abstract stack
unwinding api usage.

Suggested-by: Ilya Leoshkevich 
Reviewed-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik