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Subject[PATCH 4.4 71/91] KVM: x86: Protect kvm_lapic_reg_write() from Spectre-v1/L1TF attacks
Date
From: Marios Pomonis <pomonis@google.com>

[ Upstream commit 4bf79cb089f6b1c6c632492c0271054ce52ad766 ]

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

Signed-off-by: Nick Finco <nifi@google.com>
Signed-off-by: Marios Pomonis <pomonis@google.com>
Reviewed-by: Andrew Honig <ahonig@google.com>
Cc: stable@vger.kernel.org
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/lapic.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 3c70f6c76d3a2..ce8c4ae25c157 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -36,6 +36,7 @@
#include <asm/delay.h>
#include <linux/atomic.h>
#include <linux/jump_label.h>
+#include <linux/nospec.h>
#include "kvm_cache_regs.h"
#include "irq.h"
#include "trace.h"
@@ -1432,15 +1433,21 @@ static int apic_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];
apic_set_reg(apic, reg, val);
-
break;
+ }

case APIC_LVTT:
if (!kvm_apic_sw_enabled(apic))
--
2.20.1


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