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[Qemu-devel] [PATCH 00/34] linux-user: Fix signal race conditions and SA


From: Timothy E Baldwin
Subject: [Qemu-devel] [PATCH 00/34] linux-user: Fix signal race conditions and SA_RESTART
Date: Sun, 6 Sep 2015 00:56:54 +0100

There are many races with signals in linux user:

 - Multiple host signals in quick succession, fixed by keeping host signals
   blocked, and checking if target signals are blocked before calling
   target signal handler.
 - Signal shortly before blocking system call, fixed by either:
   - Block hosts signals, check and use host system call with
     sigset_t parameter.
   - Or check if signals are pending immediately before host system call
     and if a signal arrives between the check and system call rewind
     host instruction pointer to before the check. Also fixes SA_RESTART.
 - Signal before or during sensitive system call, fixed in a similar manner.
 - Close host and synchronous signals, partly fixed by implementing a separate
   queue for synchronous signals which are dispatched first. The asynchronous
   signal may still be delayed or lost rather than dispatched to another thread
   or handled after exec().

Also fixed:
 - Errno array bounds.
 - Default fatal actions occurring in the middle of target instructions.
 
I have major problems testing the system call restarting:
 - x86, ARM MIPS, PowerPC and SPARC sucessful tested.
 - Microblaze and SH4 works without signals, but signal test case
   crashes with or without my changes.
 - Alpha works without signals, but don't have a toolchain.
   to compile the signal test case.
 - I have been unable to test UniCore32, OpenRISC, M68K, S390
   and CRIS due to a lack of binaries and toolchains.
   
Help would be appreciated - this is the only change I intend to make
to unshared code to all targets.

Outstanding issues:
 - The remaining blocking target system calls.
 - Fatal default actions may be delayed in a broken blocking target
   system call.
 
Timothy E Baldwin (34):
  linux-user: Fix array bounds in errno conversion
  linux-user: Reindent signal handling
  linux-user: Support for restarting system calls
  linux-user: Support for restarting system calls for x86 targets
  linux-user: Support for restarting system calls for ARM targets
  linux-user: Support for restarting system calls for MIPS targets
  linux-user: Support for restarting system calls for PPC targets
  linux-user: Support for restarting system calls for SPARC targets
  linux-user: Test for restarting system calls
  linux-user: Support for restarting system calls for Microblaze targets
  linux-user: Support for restarting system calls for SH4 targets
  linux-user: Support for restarting system calls for APLHA targets
  linux-user: Fix signal before blocking system calls race and
    SA_RESTART
  linux-user: Use safe_syscall for read and write system calls
  linux-user: Remove redundant get_errno() calls
  linux-user: Use safe_syscall for open and openat system calls
  linux-user: Use safe_syscall for wait system calls
  linux-user: Fix race between multiple signals
  linux-user: Restart fork() if signals pending
  linux-user: Remove redundant default action check in queue_signal()
  linux-user: Remove redundant gdb_queuesig()
  linux-user: Remove real-time signal queuing
  linux-user: Queue synchronous signals separately
  linux-user: Restart execve() if signal pending
  linux-user: Restart exit() if signal pending
  linux-user: Restart kill() if signal pending
  linux-user: pause() should not pause if signal pending
  linux-user: Restart sigaction() if signal pending
  linux-user: Support for restarting system calls for UniCore32 targets
  linux-user: Support for restarting system calls for OpenRISC targets
  linux-user: Support for restarting system calls for M68K targets
  linux-user: Support for restarting system calls for S390 targets
  linux-user: Support for restarting system calls for CRIS targets
  linux-user: Remove TARGET_USE_ERESTARTSYS

 configure                        |   13 +
 gdbstub.c                        |   13 -
 include/exec/gdbstub.h           |    1 -
 linux-user/Makefile.objs         |    3 +-
 linux-user/errno_defs.h          |    3 +
 linux-user/main.c                |  210 ++--
 linux-user/mips/syscall.h        |    4 -
 linux-user/mips64/syscall.h      |    4 -
 linux-user/ppc/syscall.h         |    2 -
 linux-user/qemu.h                |   37 +-
 linux-user/safe_syscall/x86_64.S |   34 +
 linux-user/signal.c              | 2012 +++++++++++++++++++-------------------
 linux-user/syscall.c             |  247 ++++-
 13 files changed, 1422 insertions(+), 1161 deletions(-)
 create mode 100644 linux-user/safe_syscall/x86_64.S

-- 
2.1.4




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