KVM: x86: Protect DR-based index computations from Spectre-v1/L1TF attacks

commit ea740059ecb37807ba47b84b33d1447435a8d868 upstream.

This fixes a Spectre-v1/L1TF vulnerability in __kvm_set_dr() and
kvm_get_dr().
Both kvm_get_dr() and kvm_set_dr() (a wrapper of __kvm_set_dr()) are
exported symbols so KVM should tream them conservatively from a security
perspective.

Fixes: 020df0794f57 ("KVM: move DR register access handling into generic code")

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index df7ccee..6117979 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -53,6 +53,7 @@
 #include <linux/pvclock_gtod.h>
 #include <linux/kvm_irqfd.h>
 #include <linux/irqbypass.h>
+#include <linux/nospec.h>
 #include <trace/events/kvm.h>
 
 #define CREATE_TRACE_POINTS
@@ -873,9 +874,11 @@ static u64 kvm_dr6_fixed(struct kvm_vcpu *vcpu)
 
 static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 {
+       size_t size = ARRAY_SIZE(vcpu->arch.db);
+
        switch (dr) {
        case 0 ... 3:
-               vcpu->arch.db[dr] = val;
+               vcpu->arch.db[array_index_nospec(dr, size)] = val;
                if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
                        vcpu->arch.eff_db[dr] = val;
                break;
@@ -912,9 +915,11 @@ EXPORT_SYMBOL_GPL(kvm_set_dr);
 
 int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
 {
+       size_t size = ARRAY_SIZE(vcpu->arch.db);
+
        switch (dr) {
        case 0 ... 3:
-               *val = vcpu->arch.db[dr];
+               *val = vcpu->arch.db[array_index_nospec(dr, size)];
                break;
        case 4:
                /* fall through */