From: Josh Poimboeuf <jpoimboe@kernel.org>

Date: Tue, 14 Jun 2022 15:07:19 -0700

Subject: x86/bugs: Do IBPB fallback check only once

Git-commit: 0fe4aeea9c01baabecc8c3afc7889c809d939bc2

Patch-mainline: v5.19-rc4

References: bsc#1199657 CVE-2022-29900 CVE-2022-29901

When booting with retbleed=auto, if the kernel wasn't built with

CONFIG_CC_HAS_RETURN_THUNK, the mitigation falls back to IBPB.  Make

sure a warning is printed in that case.  The IBPB fallback check is done

twice, but it really only needs to be done once.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Signed-off-by: Borislav Petkov <bp@suse.de>

---

 arch/x86/kernel/cpu/bugs.c | 15 +++++----------

 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c

index 04077d13b3ae..108bd74289c5 100644

--- a/arch/x86/kernel/cpu/bugs.c

+++ b/arch/x86/kernel/cpu/bugs.c

@@ -891,18 +891,13 @@ static void __init retbleed_select_mitigation(void)

 	case RETBLEED_CMD_AUTO:

 	default:

 		if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||

-		    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {

-

-			if (IS_ENABLED(CONFIG_RETPOLINE) &&

-			    IS_ENABLED(CONFIG_CC_HAS_RETURN_THUNK))

-				retbleed_mitigation = RETBLEED_MITIGATION_UNRET;

-			else

-				retbleed_mitigation = RETBLEED_MITIGATION_IBPB;

-		}

+		    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)

+			retbleed_mitigation = RETBLEED_MITIGATION_UNRET;

 		/*

-		 * The Intel mitigation (IBRS) was already selected in

-		 * spectre_v2_select_mitigation().

+		 * The Intel mitigation (IBRS or eIBRS) was already selected in

+		 * spectre_v2_select_mitigation().  'retbleed_mitigation' will

+		 * be set accordingly below.

 		 */

 		break;