[PATCH 5.4 17/23] KVM: x86: use array_index_nospec with indices that come from guest

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thijs Raymakers <thijs@raymakers.nl>

commit c87bd4dd43a624109c3cc42d843138378a7f4548 upstream.

min and dest_id are guest-controlled indices. Using array_index_nospec()
after the bounds checks clamps these values to mitigate speculative execution
side-channels.

Signed-off-by: Thijs Raymakers <thijs@raymakers.nl>
Cc: stable@vger.kernel.org
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: 715062970f37 ("KVM: X86: Implement PV sched yield hypercall")
Fixes: bdf7ffc89922 ("KVM: LAPIC: Fix pv ipis out-of-bounds access")
Fixes: 4180bf1b655a ("KVM: X86: Implement "send IPI" hypercall")
Link: https://lore.kernel.org/r/20250804064405.4802-1-thijs@raymakers.nl
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kvm/lapic.c |    3 +++
 arch/x86/kvm/x86.c   |    7 +++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -589,6 +589,9 @@ int kvm_pv_send_ipi(struct kvm *kvm, uns
 
 	if (min > map->max_apic_id)
 		goto out;
+
+	min = array_index_nospec(min, map->max_apic_id + 1);
+
 	/* Bits above cluster_size are masked in the caller.  */
 	for_each_set_bit(i, &ipi_bitmap_low,
 		min((u32)BITS_PER_LONG, (map->max_apic_id - min + 1))) {
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7506,8 +7506,11 @@ static void kvm_sched_yield(struct kvm *
 	rcu_read_lock();
 	map = rcu_dereference(kvm->arch.apic_map);
 
-	if (likely(map) && dest_id <= map->max_apic_id && map->phys_map[dest_id])
-		target = map->phys_map[dest_id]->vcpu;
+	if (likely(map) && dest_id <= map->max_apic_id) {
+		dest_id = array_index_nospec(dest_id, map->max_apic_id + 1);
+		if (map->phys_map[dest_id])
+			target = map->phys_map[dest_id]->vcpu;
+	}
 
 	rcu_read_unlock();