From: Kim Phillips <kim.phillips@amd.com>
Date: Mon, 28 Feb 2022 17:23:15 +0000 (-0600)
Subject: x86/speculation: Use generic retpoline by default on AMD
X-Git-Tag: v4.14.271~25
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=85938688be23ecd36a06757096896b2779b80d97;p=thirdparty%2Fkernel%2Fstable.git

x86/speculation: Use generic retpoline by default on AMD

commit 244d00b5dd4755f8df892c86cab35fb2cfd4f14b 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: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 383ea4440aac6..b77daef95cb28 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/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;
 }