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Gustavo Luiz Duarte 04e3f1d1e1 powerpc/tm: Fix clearing MSR[TS] in current when reclaiming on signal delivery 
commit 2464cc4c34 upstream.

After a treclaim, we expect to be in non-transactional state. If we
don't clear the current thread's MSR[TS] before we get preempted, then
tm_recheckpoint_new_task() will recheckpoint and we get rescheduled in
suspended transaction state.

When handling a signal caught in transactional state,
handle_rt_signal64() calls get_tm_stackpointer() that treclaims the
transaction using tm_reclaim_current() but without clearing the
thread's MSR[TS]. This can cause the TM Bad Thing exception below if
later we pagefault and get preempted trying to access the user's
sigframe, using __put_user(). Afterwards, when we are rescheduled back
into do_page_fault() (but now in suspended state since the thread's
MSR[TS] was not cleared), upon executing 'rfid' after completion of
the page fault handling, the exception is raised because a transition
from suspended to non-transactional state is invalid.

  Unexpected TM Bad Thing exception at c00000000000de44 (msr 0x8000000302a03031) tm_scratch=800000010280b033
  Oops: Unrecoverable exception, sig: 6 [#1]
  LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
  CPU: 25 PID: 15547 Comm: a.out Not tainted 5.4.0-rc2 #32
  NIP:  c00000000000de44 LR: c000000000034728 CTR: 0000000000000000
  REGS: c00000003fe7bd70 TRAP: 0700   Not tainted  (5.4.0-rc2)
  MSR:  8000000302a03031 <SF,VEC,VSX,FP,ME,IR,DR,LE,TM[SE]>  CR: 44000884  XER: 00000000
  CFAR: c00000000000dda4 IRQMASK: 0
  PACATMSCRATCH: 800000010280b033
  GPR00: c000000000034728 c000000f65a17c80 c000000001662800 00007fffacf3fd78
  GPR04: 0000000000001000 0000000000001000 0000000000000000 c000000f611f8af0
  GPR08: 0000000000000000 0000000078006001 0000000000000000 000c000000000000
  GPR12: c000000f611f84b0 c00000003ffcb200 0000000000000000 0000000000000000
  GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR20: 0000000000000000 0000000000000000 0000000000000000 c000000f611f8140
  GPR24: 0000000000000000 00007fffacf3fd68 c000000f65a17d90 c000000f611f7800
  GPR28: c000000f65a17e90 c000000f65a17e90 c000000001685e18 00007fffacf3f000
  NIP [c00000000000de44] fast_exception_return+0xf4/0x1b0
  LR [c000000000034728] handle_rt_signal64+0x78/0xc50
  Call Trace:
  [c000000f65a17c80] [c000000000034710] handle_rt_signal64+0x60/0xc50 (unreliable)
  [c000000f65a17d30] [c000000000023640] do_notify_resume+0x330/0x460
  [c000000f65a17e20] [c00000000000dcc4] ret_from_except_lite+0x70/0x74
  Instruction dump:
  7c4ff120 e8410170 7c5a03a6 38400000 f8410060 e8010070 e8410080 e8610088
  60000000 60000000 e8810090 e8210078 <4c000024> 48000000 e8610178 88ed0989
  ---[ end trace 93094aa44b442f87 ]---

The simplified sequence of events that triggers the above exception is:

  ...				# userspace in NON-TRANSACTIONAL state
  tbegin			# userspace in TRANSACTIONAL state
  signal delivery		# kernelspace in SUSPENDED state
  handle_rt_signal64()
    get_tm_stackpointer()
      treclaim			# kernelspace in NON-TRANSACTIONAL state
    __put_user()
      page fault happens. We will never get back here because of the TM Bad Thing exception.

  page fault handling kicks in and we voluntarily preempt ourselves
  do_page_fault()
    __schedule()
      __switch_to(other_task)

  our task is rescheduled and we recheckpoint because the thread's MSR[TS] was not cleared
  __switch_to(our_task)
    switch_to_tm()
      tm_recheckpoint_new_task()
        trechkpt			# kernelspace in SUSPENDED state

  The page fault handling resumes, but now we are in suspended transaction state
  do_page_fault()    completes
  rfid     <----- trying to get back where the page fault happened (we were non-transactional back then)
  TM Bad Thing			# illegal transition from suspended to non-transactional

This patch fixes that issue by clearing the current thread's MSR[TS]
just after treclaim in get_tm_stackpointer() so that we stay in
non-transactional state in case we are preempted. In order to make
treclaim and clearing the thread's MSR[TS] atomic from a preemption
perspective when CONFIG_PREEMPT is set, preempt_disable/enable() is
used. It's also necessary to save the previous value of the thread's
MSR before get_tm_stackpointer() is called so that it can be exposed
to the signal handler later in setup_tm_sigcontexts() to inform the
userspace MSR at the moment of the signal delivery.

Found with tm-signal-context-force-tm kernel selftest.

Fixes: 2b0a576d15 ("powerpc: Add new transactional memory state to the signal context")
Cc: stable@vger.kernel.org # v3.9
Signed-off-by: Gustavo Luiz Duarte <gustavold@linux.ibm.com>
Acked-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200211033831.11165-1-gustavold@linux.ibm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2020-02-28 17:22:17 +01:00
Documentation fbdev: fix numbering of fbcon options 2020-02-24 08:36:42 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch powerpc/tm: Fix clearing MSR[TS] in current when reclaiming on signal delivery 2020-02-28 17:22:17 +01:00
block block, bfq: do not plug I/O for bfq_queues with no proc refs 2020-02-24 08:36:31 +01:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: essiv - fix AEAD capitalization and preposition use in help text 2020-02-24 08:36:50 +01:00
drivers drm/panfrost: perfcnt: Reserve/use the AS attached to the perfcnt MMU context 2020-02-28 17:22:17 +01:00
fs btrfs: handle logged extent failure properly 2020-02-28 17:22:13 +01:00
include USB: core: add endpoint-blacklist quirk 2020-02-28 17:22:16 +01:00
init Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:34:53 +00:00
ipc ipc/msg.c: consolidate all xxxctl_down() functions 2020-02-11 04:35:07 -08:00
kernel trigger_next should increase position index 2020-02-24 08:36:59 +01:00
lib lib/scatterlist.c: adjust indentation in __sg_alloc_table 2020-02-24 08:37:00 +01:00
mm mm/mmu_gather: invalidate TLB correctly on batch allocation failure and flush 2020-02-11 04:35:42 -08:00
net sunrpc: Fix potential leaks in sunrpc_cache_unhash() 2020-02-24 08:36:55 +01:00
samples samples/bpf: Set -fno-stack-protector when building BPF programs 2020-02-24 08:36:36 +01:00
scripts bpf, btf: Always output invariant hit in pahole DWARF to BTF transform 2020-02-24 08:36:55 +01:00
security selinux: ensure we cleanup the internal AVC counters on error in avc_update() 2020-02-24 08:36:39 +01:00
sound ASoC: sun8i-codec: Fix setting DAI data format 2020-02-28 17:22:13 +01:00
tools selftests/eeh: Bump EEH wait time to 60s 2020-02-24 08:36:57 +01:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-09 10:20:00 +01:00
virt KVM: arm64: Treat emulated TVAL TimerValue as a signed 32-bit integer 2020-02-14 16:34:18 -05:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: correct entries for ISDN/mISDN section 2020-02-11 04:35:06 -08:00
Makefile Linux 5.4.22 2020-02-24 08:37:04 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.