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From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Date: Thu, 7 Jul 2022 13:41:52 -0300
Subject: x86/bugs: Do not enable IBPB-on-entry when IBPB is not supported
Origin: https://git.kernel.org/linus/2259da159fbe5dba8ac00b560cf00b6a6537fa18
There are some VM configurations which have Skylake model but do not
support IBPB. In those cases, when using retbleed=ibpb, userspace is going
to be killed and kernel is going to panic.
If the CPU does not support IBPB, warn and proceed with the auto option. Also,
do not fallback to IBPB on AMD/Hygon systems if it is not supported.
Fixes: 3ebc17006888 ("x86/bugs: Add retbleed=ibpb")
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/kernel/cpu/bugs.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index cf08a1b8f3c7..d26c57d98b98 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -865,7 +865,10 @@ static void __init retbleed_select_mitigation(void)
break;
case RETBLEED_CMD_IBPB:
- if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
+ if (!boot_cpu_has(X86_FEATURE_IBPB)) {
+ pr_err("WARNING: CPU does not support IBPB.\n");
+ goto do_cmd_auto;
+ } else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
} else {
pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
@@ -880,7 +883,7 @@ static void __init retbleed_select_mitigation(void)
boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
if (IS_ENABLED(CONFIG_CPU_UNRET_ENTRY))
retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
- else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY))
+ else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY) && boot_cpu_has(X86_FEATURE_IBPB))
retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
}
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