[PATCH 5.18 38/61] x86/bugs: Do IBPB fallback check only once

Greg Kroah-Hartman
2022-07-12T19:16:08Z

From: Josh Poimboeuf <jpoimboe@kernel.org>

commit 0fe4aeea9c01baabecc8c3afc7889c809d939bc2 upstream.

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>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/cpu/bugs.c | 15 +++++----------
1 file changed, 5 insertions(+), 10 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -884,18 +884,13 @@ static void __init retbleed_select_mitig
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;