[Qemu-devel] [PATCH v2 00/28] linux-user: fix race between signals and syscalls

[Peter Maydell]

This patch series is an updated version of the original series
sent by Timothy Baldwin in autumn of last year
(https://lists.gnu.org/archive/html/qemu-devel/2015-09/msg01388.html).
I have attempted to address various code review comments made on that
original patchset.

Changes v1->v2:
 * more description in comments and commit messages of what is going on
 * implement restarting for all guest architectures (tilegx wasn't
   in the tree when v1 was sent out)
 * reordered the patches in the series a bit; in particular we add
   support for restarting syscalls to all targets and so we don't
   need the TARGET_USE_ERESTARTSYS define
 * fixed a bug in the Alpha restart code where we were incorrectly
   treating env->ir[IR_PV] as the PC, not env->pc
 * restrict scope of patchset to just providing and using the
   safe_syscall mechanism. (I plan to upstream the other race fixes
   in the second half of Timothy's patchset separately once this lot
   are in.)
 * avoid per-architecture if-ladders in configure and C code by
   creating a linux-user/host/$(HOSTARCH) type directory structure
   so the makefiles can pull in the right files for the host
   automatically
 * added patches to use safe_syscall for futex, select and pselect
   (in particular fixing futex() allows binaries that use the Boehm
   garbage collector, like the Mono runtime, to work)
 * include a patch which sets r14 on exit from microblaze syscalls,
   which I think clarifies how that architecture does things
   (though it is not ABI-wise strictly required)
 * fixed bug in wrapping of waitid syscall -- it has five args, not four
 * switched safe_syscall() to use a "return -1 and set errno"
   convention for failure; this matches syscall(), and seemed to
   me to be more intuitive for switching code around and for when
   there's a mix of code paths using safe_syscall() and directly
   calling libc functions (though it does mean that we push error
   numbers into errno and then fish them out again later)
 * added the magic GNU-stack rune that avoids incorrectly tainting
   our whole binary as "needs an executable stack" when an asm
   file is linked into it

Notes:
 * safe_syscall is supported for all guest architectures, but
   only the x86_64 host architecture; adding the asm fragment
   for our other hosts should be straightforward
 * there are a fair number of other system calls that should be
   using safe_syscall too
In both cases I thought it was better to avoid making this patchset
any larger or later; we can easily do these in later patches if
the general concept and mechanism has made it into master.


I've tested mostly by running the LTP test suite for 32-bit ARM
guests; this patchset neither improves nor worsens our pass rate.

I think the fixing of select/pselect ought to deal with hangs when
running cmake (https://bugs.launchpad.net/qemu/+bug/955379), but
I have no reliable reproducer for that bug so can't say for sure.
The "Mono hangs due to it using Boehm GC" bug is
https://bugs.launchpad.net/ubuntu/+source/qemu-kvm/+bug/530000
and that is definitely fixed by this patchset.


thanks
-- PMM

Peter Maydell (5):
  linux-user: Consistently return host errnos from do_openat()
  linux-user: Support for restarting system calls for tilegx targets
  linux-user: Set r14 on exit from microblaze syscall
  linux-user: Use safe_syscall for pselect, select syscalls
  linux-user: Use safe_syscall for futex syscall

Timothy E Baldwin (23):
  linux-user: Check array bounds in errno conversion
  linux-user: Reindent signal handling
  linux-user: Define TARGET_ERESTART* errno values
  linux-user: Renumber TARGET_QEMU_ESIGRETURN, make it not arch-specific
  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: Support for restarting system calls for SH4 targets
  linux-user: Support for restarting system calls for Alpha targets
  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: Support for restarting system calls for Microblaze targets
  linux-user: Add debug code to exercise restarting system calls
  linux-user: Provide safe_syscall for fixing races between signals and
    syscalls
  linux-user: Use safe_syscall for read and write system calls
  linux-user: Use safe_syscall for open and openat system calls
  linux-user: Use safe_syscall for wait system calls
  linux-user: Use safe_syscall for execve syscall

 Makefile.target                           |    4 +-
 linux-user/Makefile.objs                  |    3 +-
 linux-user/alpha/target_signal.h          |    1 +
 linux-user/arm/target_signal.h            |    1 +
 linux-user/cris/target_signal.h           |    1 +
 linux-user/errno_defs.h                   |   17 +
 linux-user/host/x86_64/hostdep.h          |   38 +
 linux-user/host/x86_64/safe-syscall.inc.S |   81 ++
 linux-user/m68k/target_signal.h           |    1 +
 linux-user/main.c                         |  225 ++--
 linux-user/microblaze/target_signal.h     |    1 +
 linux-user/mips/target_signal.h           |    1 +
 linux-user/mips/target_syscall.h          |    4 -
 linux-user/mips64/target_signal.h         |    1 +
 linux-user/mips64/target_syscall.h        |    4 -
 linux-user/openrisc/target_signal.h       |    1 +
 linux-user/ppc/target_signal.h            |    1 +
 linux-user/ppc/target_syscall.h           |    2 -
 linux-user/qemu.h                         |  127 ++-
 linux-user/s390x/target_signal.h          |    1 +
 linux-user/safe-syscall.S                 |   30 +
 linux-user/sh4/target_signal.h            |    1 +
 linux-user/signal.c                       | 1610 +++++++++++++++--------------
 linux-user/sparc/target_signal.h          |    1 +
 linux-user/sparc64/target_signal.h        |    1 +
 linux-user/syscall.c                      |  188 +++-
 linux-user/tilegx/target_signal.h         |    1 +
 27 files changed, 1428 insertions(+), 919 deletions(-)
 create mode 100644 linux-user/host/x86_64/hostdep.h
 create mode 100644 linux-user/host/x86_64/safe-syscall.inc.S
 create mode 100644 linux-user/safe-syscall.S

-- 
1.9.1