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[Xen-devel] [PATCH v6 0/4] x86: modify_ldt improvement, test, and config option

This is intended for x86/urgent.  Sorry for taking so long, but it
seemed nice to avoid breaking Xen.

This fixes the "dazed and confused" issue which was exposed by the
CVE-2015-5157 fix.  It's also probably a good general attack surface
reduction, and it replaces some scary code with IMO less scary code.

Also, servers and embedded systems should probably turn off modify_ldt.
This makes that possible.

Xen people, can you test patch 1?  It works for me on my evil 32-bit
Xen virtio setup.

Willy and Kees: I left the config option alone.  The -tiny people will
like it, and we can always add a sysctl of some sort later.

Changes from v5:
 - Improve Xen bits, this time with comments that seem plausible.
 - Fix debug_locks warning on exec.
 - Add a test for exec preserving the LDT (!)

Changes from v4:
 - Fix Xen even better (patch 1 is new).
 - Reorder the patches to make a little more sense.

Changes from v3:
 - Hopefully fixed Xen.
 - Fixed 32-bit test case on 32-bit native kernel.
 - Fix bogus vumnap for some LDT sizes.
 - Strengthen test case to check all LDT sizes (catches bogus vunmap).
 - Lots of cleanups, mostly from Borislav.
 - Simplify IPI code using on_each_cpu_mask.

Changes from v2:
 - Allocate ldt_struct and the LDT entries separately.  This should fix Xen.
 - Stop using write_ldt_entry, since I'm pretty sure it's unnecessary now
   that we no longer mutate an in-use LDT.  (Xen people, can you check?)

Changes from v1:
 - The config option is new.
 - The test case is new.
 - Fixed a missing allocation failure check.
 - Fixed a use-after-free on fork().

Andy Lutomirski (4):
  x86/xen: Probe target addresses in set_aliased_prot before the
  x86/ldt: Make modify_ldt synchronous
  selftests/x86, x86/ldt: Add a selftest for modify_ldt
  x86/ldt: Make modify_ldt optional

 arch/x86/Kconfig                      |  17 +
 arch/x86/include/asm/desc.h           |  15 -
 arch/x86/include/asm/mmu.h            |   5 +-
 arch/x86/include/asm/mmu_context.h    |  68 +++-
 arch/x86/kernel/Makefile              |   3 +-
 arch/x86/kernel/cpu/common.c          |   4 +-
 arch/x86/kernel/cpu/perf_event.c      |  16 +-
 arch/x86/kernel/ldt.c                 | 262 +++++++++-------
 arch/x86/kernel/process_64.c          |   6 +-
 arch/x86/kernel/step.c                |   8 +-
 arch/x86/power/cpu.c                  |   3 +-
 arch/x86/xen/enlighten.c              |  40 +++
 kernel/sys_ni.c                       |   1 +
 tools/testing/selftests/x86/Makefile  |   2 +-
 tools/testing/selftests/x86/ldt_gdt.c | 576 ++++++++++++++++++++++++++++++++++
 15 files changed, 871 insertions(+), 155 deletions(-)
 create mode 100644 tools/testing/selftests/x86/ldt_gdt.c


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