x86: add support for STAC/CLAC instructions

The STAC/CLAC instructions are only available when SMAP feature is
available, but on the other hand they aren't needed if SMAP is not
enabled, or before we start to run userspace, in that case, the
functions and macros do nothing.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
x86: clear AC bit in RFLAGS to protect Xen itself by SMAP

Clear AC bit in RFLAGS at the beginning of exception, interrupt, hypercall,
so Xen itself can be protected by SMAP mechanism. This patch also sets AC
bit at the beginning of double_fault and fatal_trap() to reduce the likelihood
of taking a further fault while trying to dump state.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
x86: temporarily disable SMAP to legally access user pages in kernel mode

Use STAC/CLAC to temporarily disable SMAP to allow legal accesses to
user pages in kernel mode

STAC/CLAC is not needed for compat_create_bounce_frame, since in this
chunk of code, it only accesses the pv guest's kernel stack, which is
in ring 1 for 32-bit pv guests.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
VMX: disable SMAP feature when guest is in non-paging mode

SMAP is disabled if CPU is in non-paging mode in hardware.
However Xen always uses paging mode to emulate guest non-paging
mode with HAP. To emulate this behavior, SMAP needs to be manually
disabled when guest switches to non-paging mode.

This logic is similiar with SMEP.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
x86: enable Supervisor Mode Access Prevention (SMAP) for Xen

Supervisor Mode Access Prevention (SMAP) is a new security
feature disclosed by Intel, please refer to the following
document:

http://software.intel.com/sites/default/files/319433-014.pdf

If CR4.SMAP = 1, supervisor-mode data accesses are not allowed
to linear addresses that are accessible in user mode. If CPL < 3,
SMAP protections are disabled if EFLAGS.AC = 1. If CPL = 3, SMAP
applies to all supervisor-mode data accesses (these are implicit
supervisor accesses) regardless of the value of EFLAGS.AC.

This patch enables SMAP in Xen to prevent Xen hypervisor from
accessing pv guest data, whose translation paging-structure
entries' U/S flags are all set.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
x86/hvm: add SMAP support to HVM guest

Intel new CPU supports SMAP (Supervisor Mode Access Prevention).
SMAP prevents supervisor-mode accesses to any linear address with
a valid translation for which the U/S flag (bit 2) is 1 in every
paging-structure entry controlling the translation for the linear
address.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Tim Deegan <tim@xen.org>
x86/tools: expose SMAP to HVM guests

This patch exposes SMAP festure to HVM guests

Signed-off-by: Feng Wu <feng.wu@intel.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
x86/traps: do not inline do_trap() into 10 different handlers

Furthermore, trapnr can be pulled from regs->entry_vector to avoid a risk of
mismatching the trap number with the underlying exception state.

This nets 2K of code reduction.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>