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: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Amit Shah <amit.shah@amd.com>
Reviewed-by: Nikolay 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

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 99265098d04507d13c61f6f733f870dd1c12a31d..a10b37bb747ed0ed6b7708abddd363849c4ae96d 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -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;
        }