x86/CPU/AMD: Fix the DIV(0) initial fix attempt

stable inclusion
from stable-v5.10.192
commit 69712baf249570a1419e75dc1a103a44e375b2cd
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I7WY4J
CVE: CVE-2023-20588

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69712baf249570a1419e75dc1a103a44e375b2cd



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

commit f58d6fbc upstream.

Initially, it was thought that doing an innocuous division in the #DE
handler would take care to prevent any leaking of old data from the
divider but by the time the fault is raised, the speculation has already
advanced too far and such data could already have been used by younger
operations.

Therefore, do the innocuous division on every exit to userspace so that
userspace doesn't see any potentially old data from integer divisions in
kernel space.

Do the same before VMRUN too, to protect host data from leaking into the
guest too.

Fixes: 77245f1c ("x86/CPU/AMD: Do not leak quotient data after a division by 0")
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20230811213824.10025-1-bp@alien8.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>