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Improper use of userspace_irqchip_in_use led to syzbot hitting the
following WARN_ON() in kvm_timer_update_irq():
WARNING: CPU: 0 PID: 3281 at arch/arm64/kvm/arch_timer.c:459
kvm_timer_update_irq+0x21c/0x394
Call trace:
kvm_timer_update_irq+0x21c/0x394 arch/arm64/kvm/arch_timer.c:459
kvm_timer_vcpu_reset+0x158/0x684 arch/arm64/kvm/arch_timer.c:968
kvm_reset_vcpu+0x3b4/0x560 arch/arm64/kvm/reset.c:264
kvm_vcpu_set_target arch/arm64/kvm/arm.c:1553 [inline]
kvm_arch_vcpu_ioctl_vcpu_init arch/arm64/kvm/arm.c:1573 [inline]
kvm_arch_vcpu_ioctl+0x112c/0x1b3c arch/arm64/kvm/arm.c:1695
kvm_vcpu_ioctl+0x4ec/0xf74 virt/kvm/kvm_main.c:4658
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl fs/ioctl.c:893 [inline]
__arm64_sys_ioctl+0x108/0x184 fs/ioctl.c:893
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x78/0x1b8 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xe8/0x1b0 arch/arm64/kernel/syscall.c:132
do_el0_svc+0x40/0x50 arch/arm64/kernel/syscall.c:151
el0_svc+0x54/0x14c arch/arm64/kernel/entry-common.c:712
el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
The following sequence led to the scenario:
- Userspace creates a VM and a vCPU.
- The vCPU is initialized with KVM_ARM_VCPU_PMU_V3 during
KVM_ARM_VCPU_INIT.
- Without any other setup, such as vGIC or vPMU, userspace issues
KVM_RUN on the vCPU. Since the vPMU is requested, but not setup,
kvm_arm_pmu_v3_enable() fails in kvm_arch_vcpu_run_pid_change().
As a result, KVM_RUN returns after enabling the timer, but before
incrementing 'userspace_irqchip_in_use':
kvm_arch_vcpu_run_pid_change()
ret = kvm_arm_pmu_v3_enable()
if (!vcpu->arch.pmu.created)
return -EINVAL;
if (ret)
return ret;
[...]
if (!irqchip_in_kernel(kvm))
static_branch_inc(&userspace_irqchip_in_use);
- Userspace ignores the error and issues KVM_ARM_VCPU_INIT again.
Since the timer is already enabled, control moves through the
following flow, ultimately hitting the WARN_ON():
kvm_timer_vcpu_reset()
if (timer->enabled)
kvm_timer_update_irq()
if (!userspace_irqchip())
ret = kvm_vgic_inject_irq()
ret = vgic_lazy_init()
if (unlikely(!vgic_initialized(kvm)))
if (kvm->arch.vgic.vgic_model !=
KVM_DEV_TYPE_ARM_VGIC_V2)
return -EBUSY;
WARN_ON(ret);
Theoretically, since userspace_irqchip_in_use's functionality can be
simply replaced by '!irqchip_in_kernel()', get rid of the static key
to avoid the mismanagement, which also helps with the syzbot issue.
Cc: <stable@vger.kernel.org>
Reported-by: syzbot <syzkaller@googlegroups.com>
Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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Handle the initialization of trap registers at the hypervisor in
pKVM, even for non-protected guests. The host is not trusted with
the values of the trap registers, regardless of the VM type.
Therefore, when switching between the host and the guests, only
flush the HCR_EL2 TWI and TWE bits. The host is allowed to
configure these for opportunistic scheduling, as neither affects
the protection of VMs or the hypervisor.
Reported-by: Will Deacon <will@kernel.org>
Fixes: 814ad8f96e92 ("KVM: arm64: Drop trapping of PAuth instructions/keys")
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20241018074833.2563674-5-tabba@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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Do not trust the state of the VM as provided by the host when
initializing the hypervisor's view of the VM sate. Initialize it
instead at EL2 to a known good and safe state, as pKVM already
does with hypervisor VCPU states.
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20241018074833.2563674-4-tabba@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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Move kvm_vcpu_enable_ptrauth() to a shared header to be used by
hypervisor code in protected mode.
No functional change intended.
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20241018074833.2563674-3-tabba@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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Move pkvm_vcpu_init_traps() to the initialization of the
hypervisor's vcpu state in init_pkvm_hyp_vcpu(), and remove the
associated hypercall.
In protected mode, traps need to be initialized whenever a VCPU
is initialized anyway, and not only for protected VMs. This also
saves an unnecessary hypercall.
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20241018074833.2563674-2-tabba@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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Now that 'kvm_vgic_global_state' is no longer needed for ICC_CTLR_EL1
emulation on machines with a broken SEIS implementation, drop the
pKVM hypervisor mapping of the page.
Note that kvm_vgic_global_state is still mapped in non-protected
hypervisor configurations (i.e. {n,h}VHE) through the rodata section
mapping.
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241022144016.27350-3-will@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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ICC_CTLR_EL1 accesses from a guest are trapped and emulated on systems
with broken SEIS support and without FEAT_GICv3_TDIR. On such systems,
we mask SEIS support in 'kvm_vgic_global_state.ich_vtr_el2' and so the
value of ICC_CTLR_EL1.SEIS visible to the guest is always zero.
Simplify the ICC_CTLR_EL1 read emulation to return 0 for the SEIS field,
rather than reading an always-zero value from the global state.
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241022144016.27350-2-will@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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Raghavendra Rao Ananta
Fuad Tabba
Will Deacon
Linus Torvalds