FAILED: patch "[PATCH] KVM: x86: Protect kvm_lapic_reg_write() from Spectre-v1/L1TF" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4bf79cb089f6b1c6c632492c0271054ce52ad766 Mon Sep 17 00:00:00 2001
From: Marios Pomonis <[email protected]>
Date: Wed, 11 Dec 2019 12:47:46 -0800
Subject: [PATCH] KVM: x86: Protect kvm_lapic_reg_write() from Spectre-v1/L1TF
attacks

This fixes a Spectre-v1/L1TF vulnerability in kvm_lapic_reg_write(). This function contains index computations based on the (attacker-controlled) MSR number.

index 88c3c0c6d1e3..865edce27a6a 100644
@@ -1960,15 +1960,20 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 	case APIC_LVTTHMR:
 	case APIC_LVTPC:
 	case APIC_LVT1:
-	case APIC_LVTERR:
+	case APIC_LVTERR: {
 		/* TODO: Check vector */
+		size_t size;
+		u32 index;
+
 		if (!kvm_apic_sw_enabled(apic))
 			val |= APIC_LVT_MASKED;
-
-		val &= apic_lvt_mask[(reg - APIC_LVTT) >> 4];
+		size = ARRAY_SIZE(apic_lvt_mask);
+		index = array_index_nospec(
+				(reg - APIC_LVTT) >> 4, size);
+		val &= apic_lvt_mask[index];
 		kvm_lapic_set_reg(apic, reg, val);
-
 		break;
+	}
 
 	case APIC_LVTT:
 		if (!kvm_apic_sw_enabled(apic))

We didn't have 1e6e2755b635 ("KVM: x86: Misc LAPIC changes to expose helper functions") in 4.4. I've fixed it and queued this patch for 4.4.

Thanks,
Sasha