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@xxxxxxxxxxxxxxx>
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Suggested-by: Marc Zyngier <maz@xxxxxxxxxx>
Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
---
v2:
- Picked the diff shared by Marc to get rid of
'userspace_irqchip_in_use' (thanks).
- Adjusted the commit message accordingly.
v1: https://lore.kernel.org/all/20241025221220.2985227-1-rananta@xxxxxxxxxx/
arch/arm64/include/asm/kvm_host.h | 2 --
arch/arm64/kvm/arch_timer.c | 3 +--
arch/arm64/kvm/arm.c | 18 +++---------------
3 files changed, 4 insertions(+), 19 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 329619c6fa961..9f96594a0e05d 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -73,8 +73,6 @@ enum kvm_mode kvm_get_mode(void);
static inline enum kvm_mode kvm_get_mode(void) { return KVM_MODE_NONE; };
#endif
-DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
-
extern unsigned int __ro_after_init kvm_sve_max_vl;
extern unsigned int __ro_after_init kvm_host_sve_max_vl;
int __init kvm_arm_init_sve(void);
diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 879982b1cc739..1215df5904185 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -206,8 +206,7 @@ void get_timer_map(struct kvm_vcpu *vcpu, struct timer_map *map)
static inline bool userspace_irqchip(struct kvm *kvm)
{
- return static_branch_unlikely(&userspace_irqchip_in_use) &&
- unlikely(!irqchip_in_kernel(kvm));
+ return unlikely(!irqchip_in_kernel(kvm));
}
static void soft_timer_start(struct hrtimer *hrt, u64 ns)
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index a0d01c46e4084..63f5c05e9dec6 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -69,7 +69,6 @@ DECLARE_KVM_NVHE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
static bool vgic_present, kvm_arm_initialised;
static DEFINE_PER_CPU(unsigned char, kvm_hyp_initialized);
-DEFINE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
bool is_kvm_arm_initialised(void)
{
@@ -503,9 +502,6 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
{
- if (vcpu_has_run_once(vcpu) && unlikely(!irqchip_in_kernel(vcpu->kvm)))
- static_branch_dec(&userspace_irqchip_in_use);
-
kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_cache);
kvm_timer_vcpu_terminate(vcpu);
kvm_pmu_vcpu_destroy(vcpu);
@@ -848,14 +844,6 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
return ret;
}
- if (!irqchip_in_kernel(kvm)) {
- /*
- * Tell the rest of the code that there are userspace irqchip
- * VMs in the wild.
- */
- static_branch_inc(&userspace_irqchip_in_use);
- }
-
/*
* Initialize traps for protected VMs.
* NOTE: Move to run in EL2 directly, rather than via a hypercall, once
@@ -1072,7 +1060,7 @@ static bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu, int *ret)
* state gets updated in kvm_timer_update_run and
* kvm_pmu_update_run below).
*/
- if (static_branch_unlikely(&userspace_irqchip_in_use)) {
+ if (unlikely(!irqchip_in_kernel(vcpu->kvm))) {
if (kvm_timer_should_notify_user(vcpu) ||
kvm_pmu_should_notify_user(vcpu)) {
*ret = -EINTR;
@@ -1194,7 +1182,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
vcpu->mode = OUTSIDE_GUEST_MODE;
isb(); /* Ensure work in x_flush_hwstate is committed */
kvm_pmu_sync_hwstate(vcpu);
- if (static_branch_unlikely(&userspace_irqchip_in_use))
+ if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
kvm_timer_sync_user(vcpu);
kvm_vgic_sync_hwstate(vcpu);
local_irq_enable();
@@ -1240,7 +1228,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
* we don't want vtimer interrupts to race with syncing the
* timer virtual interrupt state.
*/
- if (static_branch_unlikely(&userspace_irqchip_in_use))
+ if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
kvm_timer_sync_user(vcpu);
kvm_arch_vcpu_ctxsync_fp(vcpu);
base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc
--
2.47.0.163.g1226f6d8fa-goog
