x86/speculation: Use generic retpoline by default on AMD

stable inclusion
from stable-v4.19.234
commit d3cb3a6927222268a10b2f12dfb8c9444f7cc39e
category: bugfix
bugzilla: 186453, https://gitee.com/src-openeuler/kernel/issues/I50WBM
CVE: CVE-2022-0001

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

commit 244d00b5 upstream.

AMD retpoline may be susceptible to speculation. The speculation
execution window for an incorrect indirect branch prediction using
LFENCE/JMP sequence may potentially be large enough to allow
exploitation using Spectre V2.

By default, don't use retpoline,lfence on AMD.  Instead, use the
generic retpoline.
Signed-off-by: NKim Phillips <kim.phillips@amd.com>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jiahao <chenjiahao16@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Reviewed-by: NLiao Chang <liaochang1@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

arch/x86/kernel/cpu/bugs.c

@@ -898,14 +898,6 @@ static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
 		return SPECTRE_V2_NONE;
 	}
 
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
-		if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
-			pr_err("LFENCE not serializing, switching to generic retpoline\n");
-			return SPECTRE_V2_RETPOLINE;
-		}
-		return SPECTRE_V2_LFENCE;
-	}
-
 	return SPECTRE_V2_RETPOLINE;
 }