CVE-2017-5753
CVE-2017-5715

Add speculative control support for AMD processors. For AMD, speculative
control is indicated as follows:

  CPUID EAX=0x00000007, ECX=0x00 return EDX[26] indicates support for
  both IBRS and IBPB.

  CPUID EAX=0x80000008, ECX=0x00 return EBX[12] indicates support for
  just IBPB.

On AMD family 0x10, 0x12 and 0x16 processors where either of the above
features are not supported, IBPB can be achieved by disabling
indirect branch predictor support in MSR 0xc0011021[14] at boot.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
(backported from commit 38994a3e1a9288622cb170bc89d037ca8f2b0fb6)
Signed-off-by: Andy Whitcroft <apw@canonical.com>