x86/bugs: Enable STIBP for IBPB mitigated RETBleed

stable inclusion
from stable-v5.10.137
commit fd96b61389f8650d880df4b7f8f55f880c19bff9
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd96b61389f8650d880df4b7f8f55f880c19bff9



--------------------------------

commit e6cfcdda upstream.

AMD's "Technical Guidance for Mitigating Branch Type Confusion,
Rev. 1.0 2022-07-12" whitepaper, under section 6.1.2 "IBPB On
Privileged Mode Entry / SMT Safety" says:

  Similar to the Jmp2Ret mitigation, if the code on the sibling thread
  cannot be trusted, software should set STIBP to 1 or disable SMT to
  ensure SMT safety when using this mitigation.

So, like already being done for retbleed=unret, and now also for
retbleed=ibpb, force STIBP on machines that have it, and report its SMT
vulnerability status accordingly.

 [ bp: Remove the "we" and remove "[AMD]" applicability parameter which
   doesn't work here. ]

Fixes: 3ebc1700 ("x86/bugs: Add retbleed=ibpb")
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org # 5.10, 5.15, 5.19
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
Link: https://lore.kernel.org/r/20220804192201.439596-1-kim.phillips@amd.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>