KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS

commit fc02735b upstream.

On eIBRS systems, the returns in the vmexit return path from
__vmx_vcpu_run() to vmx_vcpu_run() are exposed to RSB poisoning attacks.

Fix that by moving the post-vmexit spec_ctrl handling to immediately
after the vmexit.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>