x86/speculation: Identify processors vulnerable to SMT RSB predictions

stable inclusion
from stable-v5.15.94
commit 8f12dcab90e886d0169a9cd372a8bb35339cfc19
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6FB6C
CVE: CVE-2022-27672

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8f12dcab90e886d0169a9cd372a8bb35339cfc19



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

commit be8de49b upstream.

Certain AMD processors are vulnerable to a cross-thread return address
predictions bug. When running in SMT mode and one of the sibling threads
transitions out of C0 state, the other sibling thread could use return
target predictions from the sibling thread that transitioned out of C0.

The Spectre v2 mitigations cover the Linux kernel, as it fills the RSB
when context switching to the idle thread. However, KVM allows a VMM to
prevent exiting guest mode when transitioning out of C0. A guest could
act maliciously in this situation, so create a new x86 BUG that can be
used to detect if the processor is vulnerable.

Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <91cec885656ca1fcd4f0185ce403a53dd9edecb7.1675956146.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Guo Mengqi <guomengqi3@huawei.com>
Reviewed-by: Wang Weiyang <wangweiyang2@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>