Commit 18bae0df authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

x86/bugs: Don't fill RSB on VMEXIT with eIBRS+retpoline 



eIBRS protects against guest->host RSB underflow/poisoning attacks.
Adding retpoline to the mix doesn't change that.  Retpoline has a
balanced CALL/RET anyway.

So the current full RSB filling on VMEXIT with eIBRS+retpoline is
overkill.  Disable it or do the VMEXIT_LITE mitigation if needed.

Suggested-by: default avatarPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: default avatarAmit Shah <amit.shah@amd.com>
Reviewed-by: default avatarNikolay Borisov <nik.borisov@suse.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Link: https://lore.kernel.org/r/84a1226e5c9e2698eae1b5ade861f1b8bf3677dc.1744148254.git.jpoimboe@kernel.org
parent b1b19cfc

arch/x86/kernel/cpu/bugs.c

+4 −4
Original line number Diff line number Diff line
@@ -1617,20 +1617,20 @@ static void __init spectre_v2_determine_rsb_fill_type_at_vmexit(enum spectre_v2_ 
	case SPECTRE_V2_NONE:

		return;



	case SPECTRE_V2_EIBRS_LFENCE:

	case SPECTRE_V2_EIBRS:

	case SPECTRE_V2_EIBRS_LFENCE:

	case SPECTRE_V2_EIBRS_RETPOLINE:

		if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) {

			setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE);

			pr_info("Spectre v2 / PBRSB-eIBRS: Retire a single CALL on VMEXIT\n");

			setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE);

		}

		return;



	case SPECTRE_V2_EIBRS_RETPOLINE:

	case SPECTRE_V2_RETPOLINE:

	case SPECTRE_V2_LFENCE:

	case SPECTRE_V2_IBRS:

		setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT);

		pr_info("Spectre v2 / SpectreRSB : Filling RSB on VMEXIT\n");

		setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT);

		return;

	}