linux-kernel - [PATCH v2 06/13] KVM: x86: Protect kvm_lapic_reg

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Message-Id: <20191211204753.242298-7-pomonis@google.com>
Date:   Wed, 11 Dec 2019 12:47:46 -0800
From:   Marios Pomonis <pomonis@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, rkrcmar@...hat.com,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nick Finco <nifi@...gle.com>, Andrew Honig <ahonig@...gle.com>,
        Marios Pomonis <pomonis@...gle.com>, stable@...r.kernel.org
Subject: [PATCH v2 06/13] 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.

Fixes: commit 0105d1a52640 ("KVM: x2apic interface to lapic")

Signed-off-by: Nick Finco <nifi@...gle.com>
Signed-off-by: Marios Pomonis <pomonis@...gle.com>
Reviewed-by: Andrew Honig <ahonig@...gle.com>
Cc: stable@...r.kernel.org
---
 arch/x86/kvm/lapic.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index cf9177b4a07f..3323115f52d5 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1963,15 +1963,20 @@ 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))
-- 
2.24.0.525.g8f36a354ae-goog