From bdf7ffc89922a52a4f08a12f7421ea24bb7626a0 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Thu, 30 Aug 2018 10:03:30 +0800 Subject: [PATCH] KVM: LAPIC: Fix pv ipis out-of-bounds access MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Dan Carpenter reported that the untrusted data returns from kvm_register_read() results in the following static checker warning: arch/x86/kvm/lapic.c:576 kvm_pv_send_ipi() error: buffer underflow 'map->phys_map' 's32min-s32max' KVM guest can easily trigger this by executing the following assembly sequence in Ring0: mov $10, %rax mov $0xFFFFFFFF, %rbx mov $0xFFFFFFFF, %rdx mov $0, %rsi vmcall As this will cause KVM to execute the following code-path: vmx_handle_exit() -> handle_vmcall() -> kvm_emulate_hypercall() -> kvm_pv_send_ipi() which will reach out-of-bounds access. This patch fixes it by adding a check to kvm_pv_send_ipi() against map->max_apic_id, ignoring destinations that are not present and delivering the rest. We also check whether or not map->phys_map[min + i] is NULL since the max_apic_id is set to the max apic id, some phys_map maybe NULL when apic id is sparse, especially kvm unconditionally set max_apic_id to 255 to reserve enough space for any xAPIC ID. Reported-by: Dan Carpenter Reviewed-by: Liran Alon Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Liran Alon Cc: Dan Carpenter Signed-off-by: Wanpeng Li [Add second "if (min > map->max_apic_id)" to complete the fix. -Radim] Signed-off-by: Radim Krčmář --- arch/x86/include/asm/kvm_host.h | 2 +- arch/x86/kvm/lapic.c | 27 ++++++++++++++++++++------- 2 files changed, 21 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 3ad10f6..8e90488 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1455,7 +1455,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event); void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu); int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, - unsigned long ipi_bitmap_high, int min, + unsigned long ipi_bitmap_high, u32 min, unsigned long icr, int op_64_bit); u64 kvm_get_arch_capabilities(void); diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 0cefba2..17c0472 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -548,7 +548,7 @@ int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq, } int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, - unsigned long ipi_bitmap_high, int min, + unsigned long ipi_bitmap_high, u32 min, unsigned long icr, int op_64_bit) { int i; @@ -571,18 +571,31 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, rcu_read_lock(); map = rcu_dereference(kvm->arch.apic_map); + if (min > map->max_apic_id) + goto out; /* Bits above cluster_size are masked in the caller. */ - for_each_set_bit(i, &ipi_bitmap_low, BITS_PER_LONG) { - vcpu = map->phys_map[min + i]->vcpu; - count += kvm_apic_set_irq(vcpu, &irq, NULL); + for_each_set_bit(i, &ipi_bitmap_low, + min((u32)BITS_PER_LONG, (map->max_apic_id - min + 1))) { + if (map->phys_map[min + i]) { + vcpu = map->phys_map[min + i]->vcpu; + count += kvm_apic_set_irq(vcpu, &irq, NULL); + } } min += cluster_size; - for_each_set_bit(i, &ipi_bitmap_high, BITS_PER_LONG) { - vcpu = map->phys_map[min + i]->vcpu; - count += kvm_apic_set_irq(vcpu, &irq, NULL); + + if (min > map->max_apic_id) + goto out; + + for_each_set_bit(i, &ipi_bitmap_high, + min((u32)BITS_PER_LONG, (map->max_apic_id - min + 1))) { + if (map->phys_map[min + i]) { + vcpu = map->phys_map[min + i]->vcpu; + count += kvm_apic_set_irq(vcpu, &irq, NULL); + } } +out: rcu_read_unlock(); return count; } -- 2.7.4