x86/bugs: Do not enable IBPB-on-entry when IBPB is not supported
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>
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@ -865,7 +865,10 @@ static void __init retbleed_select_mitigation(void)
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break;
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case RETBLEED_CMD_IBPB:
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if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
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if (!boot_cpu_has(X86_FEATURE_IBPB)) {
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pr_err("WARNING: CPU does not support IBPB.\n");
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goto do_cmd_auto;
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} else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
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retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
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} else {
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pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
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@ -880,7 +883,7 @@ do_cmd_auto:
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boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
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if (IS_ENABLED(CONFIG_CPU_UNRET_ENTRY))
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retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
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else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY))
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else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY) && boot_cpu_has(X86_FEATURE_IBPB))
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retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
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}
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