[PATCH v2 06/13] KVM: x86: Protect kvm_lapic_reg_write() from Spectre-v1/L1TF attacks

Marios Pomonis
2019-12-11T20:48:52Z

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@google.com>
Signed-off-by: Marios Pomonis <pomonis@google.com>
Reviewed-by: Andrew Honig <ahonig@google.com>
Cc: stable@vger.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