[PATCH 0/4] vsyscall tweaks

[Andy Lutomirski <luto@MIT.EDU>]

With the new vsyscall emulation code, int 0xcc's behavior depends on
where it is called from.  A few dynamic instrumentation tools cleverly
copy the instruction out of the vsyscall page and execute it, resulting
in a segfault.  This is nothing new: sysenter would die in a similar way
(unless the code got lucky).  The only examples I know of are pin and
DynamoRIO -- valgrind is already smart enough not to recompile vsyscalls
0 and 1 and "smart" enough to crash unconditionally on vsyscall 2.  I
can't test pin because it refuses to run on newfangled things like Linux
3.0+ (and I don't want to muck with my kernel version to run a program
that's broken anyway).  Patch 1 in this series fixes DynamoRIO in
limited testing.

Bug reports against valgrind and DynamoRIO exist, and I haven't managed
to get permission to post to pin's message board yet.

The other three patches are minor.  Patch 2 removes compile flags that
are now unnecessary because vsyscall_64.c does not get called in user
mode.  Patch 3 wires up the getcpu syscall on x86-64 as further
encouragement to stop using the vsyscall.  Patch 4 adds a
feature-removal-schedule.txt entry suggesting that vsyscalls might be
disabled in some configurations some day.

x86 maintainers / Linus: feel free to drop any of patches 2-4.  I think
the getcpu syscall should be added, though, since it's rather odd to
have a "syscall" in the vdso and the vsyscall page that can't be called
the old-fashioned way.

Changes from RFC v2:
 - Fix some more int 0xcc references.
 - Add patches 2-4.

Andy Lutomirski (4):
  x86-64: Allow emulated vsyscalls from user addresses
  x86: Remove unnecessary compile flag tweaks for vsyscall code
  x86-64: Wire up getcpu syscall
  Add vsyscalls to feature-removal-schedule.txt

 Documentation/feature-removal-schedule.txt |   14 +++
 arch/x86/include/asm/irq_vectors.h         |   11 ++-
 arch/x86/include/asm/traps.h               |    8 ++-
 arch/x86/include/asm/unistd_64.h           |    2 +
 arch/x86/kernel/Makefile                   |   13 ---
 arch/x86/kernel/entry_64.S                 |    4 +-
 arch/x86/kernel/traps.c                    |   14 +++-
 arch/x86/kernel/vsyscall_64.c              |  131 ++++++++++++++--------------
 arch/x86/kernel/vsyscall_emu_64.S          |    6 +-
 9 files changed, 111 insertions(+), 92 deletions(-)

-- 
1.7.6