From: Kim Phillips <kim.phillips@amd.com>
Date: Mon, 28 Feb 2022 11:23:15 -0600
Subject: x86/speculation: Use generic retpoline by default on AMD
Git-commit: 244d00b5dd4755f8df892c86cab35fb2cfd4f14b
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
Patch-mainline: Queued in a subsystem tree
References: bsc#1191580 CVE-2022-0001 CVE-2022-0002

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: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/cpu/bugs.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0a4267c63d3b..a36bfe2c2480 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -941,15 +941,6 @@ static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
 		return SPECTRE_V2_NONE;
 	}
 
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
-	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
-		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;
 }