linux-kernel - [PATCH v4 0/3] x86: modify_ldt improvement, test, and config option

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Message-Id: <cover.1437802102.git.luto@kernel.org>
Date:	Fri, 24 Jul 2015 22:36:43 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	"security@...nel.org" <security@...nel.org>,
	X86 ML <x86@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	xen-devel <xen-devel@...ts.xen.org>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v4 0/3] x86: modify_ldt improvement, test, and config option

Here's v3.  It fixes the "dazed and confused" issue, I hope.  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 take a look at this?

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 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 (3):
  x86/ldt: Make modify_ldt synchronous
  x86/ldt: Make modify_ldt optional
  selftests/x86, x86/ldt: Add a selftest for modify_ldt

 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 +-
 kernel/sys_ni.c                       |   1 +
 tools/testing/selftests/x86/Makefile  |   2 +-
 tools/testing/selftests/x86/ldt_gdt.c | 492 ++++++++++++++++++++++++++++++++++
 14 files changed, 747 insertions(+), 155 deletions(-)
 create mode 100644 tools/testing/selftests/x86/ldt_gdt.c

-- 
2.4.3

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