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x86/bugs: Do not enable IBPB-on-entry when IBPB is not supported

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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>
This commit is contained in:
Thadeu Lima de Souza Cascardo 2022-07-07 13:41:52 -03:00 committed by Borislav Petkov
parent 2c08b9b38f
commit 2259da159f
1 changed files with 5 additions and 2 deletions
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7
arch/x86/kernel/cpu/bugs.c
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@ -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 @@ do_cmd_auto:
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;
}