[PATCH v3 0/3] LoongArch: KVM: irqchip fixes

[PATCH v3 0/3] LoongArch: KVM: irqchip fixes

[Tao Cui]

From: lihongfu <lihongfu@kylinos.cn>

Hi,

Three fixes for the LoongArch KVM irqchip code:

- Patch 1 clears the device pointer in the destroy callbacks: when
  KVM_CREATE_DEVICE succeeds but the following fd allocation fails
  (e.g. under RLIMIT_NOFILE), ops->destroy() frees the irqchip while
  kvm->arch.* still points to it.

- Patch 2 aligns kvm_pch_pic_create() with kvm_eiointc_create() by
  propagating the real error code; the kvm_ipi_create() counterpart is
  being fixed separately (Chaithanya Lagisetty).

- Patch 3 rejects repeated PCH-PIC CTRL_INIT with -EEXIST, using the
  initialized state of the kvm_io_device as the indicator; the MMIO
  base is only committed after a successful bus registration.

All patches carry Fixes tags.

Changes in v3:

- Drop "Load dmsintc pointer once in pch_msi_set_irq" (v2 patch 2),
  suggested by Bibo and Huacai.

- Patch 3 (v2 patch 4): reject repeated CTRL_INIT by checking the
  kvm_io_device state instead of a separate has_init flag, also
  suggested by Huacai; the check stays under slots_lock.

Changes in v2:

- Drop "Guard against NULL irqchip in irq injection" (v1 patch 2) and
  "Rebase steal time counter in vcpu context" (v1 patch 4) after
  review discussion: their trigger scenarios are not reachable
  through real VMM behaviour.

- Use the one-line destroy style in dmsintc suggested by Bibo.

- Track repeated PCH-PIC CTRL_INIT with a has_init flag and return
  -EEXIST instead of -EBUSY, also suggested by Bibo; move the check
  and base update under slots_lock so they are atomic.

Tao Cui (3):
  LoongArch: KVM: Clear device pointer in irqchip destroy callbacks
  LoongArch: KVM: Propagate real error code in kvm_pch_pic_create
  LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

 arch/loongarch/kvm/intc/dmsintc.c |  1 +
 arch/loongarch/kvm/intc/eiointc.c |  1 +
 arch/loongarch/kvm/intc/ipi.c     |  1 +
 arch/loongarch/kvm/intc/pch_pic.c | 15 +++++++++++----
 4 files changed, 14 insertions(+), 4 deletions(-)

-- 
2.43.0

[PATCH v3 1/3] LoongArch: KVM: Clear device pointer in irqchip destroy callbacks

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

The destroy callbacks of the four irqchip devices free the device
structure without clearing kvm->arch.{ipi,eiointc,pch_pic,dmsintc},
leaving a dangling pointer.  ops->destroy() is not only called at VM
teardown but also when KVM_CREATE_DEVICE succeeds and the following
anon_inode_getfd() fails (e.g. under RLIMIT_NOFILE); the VM stays
alive, kvm_arch_irqchip_in_kernel() still reports true, and interrupt
injection dereferences the freed device.

Clear the pointer when destroying.

Fixes: c532de5a67a7 ("LoongArch: KVM: Add IPI device support")
Fixes: 2e8b9df82631 ("LoongArch: KVM: Add EIOINTC device support")
Fixes: e785dfacf7e7 ("LoongArch: KVM: Add PCHPIC device support")
Fixes: 229132c309d6 ("LoongArch: KVM: Add DMSINTC device support")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 arch/loongarch/kvm/intc/dmsintc.c | 1 +
 arch/loongarch/kvm/intc/eiointc.c | 1 +
 arch/loongarch/kvm/intc/ipi.c     | 1 +
 arch/loongarch/kvm/intc/pch_pic.c | 1 +
 4 files changed, 4 insertions(+)

diff --git a/arch/loongarch/kvm/intc/dmsintc.c b/arch/loongarch/kvm/intc/dmsintc.c
index ff327b4c05f7..c182185a3d59 100644
--- a/arch/loongarch/kvm/intc/dmsintc.c
+++ b/arch/loongarch/kvm/intc/dmsintc.c
@@ -146,6 +146,7 @@ static void kvm_dmsintc_destroy(struct kvm_device *dev)
 		return;
 
 	kfree(dev->kvm->arch.dmsintc);
+	dev->kvm->arch.dmsintc = NULL;
 	kfree(dev);
 }
 
diff --git a/arch/loongarch/kvm/intc/eiointc.c b/arch/loongarch/kvm/intc/eiointc.c
index 80f78e07c74a..fe0a1918f26f 100644
--- a/arch/loongarch/kvm/intc/eiointc.c
+++ b/arch/loongarch/kvm/intc/eiointc.c
@@ -675,6 +675,7 @@ static void kvm_eiointc_destroy(struct kvm_device *dev)
 
 	kvm = dev->kvm;
 	eiointc = kvm->arch.eiointc;
+	kvm->arch.eiointc = NULL;
 	mutex_lock(&kvm->slots_lock);
 	kvm_io_bus_unregister_dev(kvm, KVM_IOCSR_BUS, &eiointc->device);
 	kvm_io_bus_unregister_dev(kvm, KVM_IOCSR_BUS, &eiointc->device_vext);
diff --git a/arch/loongarch/kvm/intc/ipi.c b/arch/loongarch/kvm/intc/ipi.c
index 80faa770c0cd..7a2dd72a4952 100644
--- a/arch/loongarch/kvm/intc/ipi.c
+++ b/arch/loongarch/kvm/intc/ipi.c
@@ -441,6 +441,7 @@ static void kvm_ipi_destroy(struct kvm_device *dev)
 
 	kvm = dev->kvm;
 	ipi = kvm->arch.ipi;
+	kvm->arch.ipi = NULL;
 	mutex_lock(&kvm->slots_lock);
 	kvm_io_bus_unregister_dev(kvm, KVM_IOCSR_BUS, &ipi->device);
 	mutex_unlock(&kvm->slots_lock);
diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
index 220fc23ffe8c..dab2d3f1b8f6 100644
--- a/arch/loongarch/kvm/intc/pch_pic.c
+++ b/arch/loongarch/kvm/intc/pch_pic.c
@@ -483,6 +483,7 @@ static void kvm_pch_pic_destroy(struct kvm_device *dev)
 
 	kvm = dev->kvm;
 	s = kvm->arch.pch_pic;
+	kvm->arch.pch_pic = NULL;
 	/* unregister pch pic device and free it's memory */
 	mutex_lock(&kvm->slots_lock);
 	kvm_io_bus_unregister_dev(kvm, KVM_MMIO_BUS, &s->device);
-- 
2.43.0

[PATCH v3 2/3] LoongArch: KVM: Propagate real error code in kvm_pch_pic_create

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

kvm_pch_pic_create() replaces the real error of
kvm_setup_default_irq_routing() with a fixed -ENOMEM.  Return the
actual code, as kvm_eiointc_create() already does; the kvm_ipi_create()
case is fixed separately by "Return the actual error code in
kvm_ipi_create()" (Chaithanya Lagisetty).

Fixes: e785dfacf7e7 ("LoongArch: KVM: Add PCHPIC device support")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
---
 arch/loongarch/kvm/intc/pch_pic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
index dab2d3f1b8f6..51e4a6a39dc0 100644
--- a/arch/loongarch/kvm/intc/pch_pic.c
+++ b/arch/loongarch/kvm/intc/pch_pic.c
@@ -444,7 +444,7 @@ static int kvm_pch_pic_create(struct kvm_device *dev, u32 type)
 
 	ret = kvm_setup_default_irq_routing(kvm);
 	if (ret)
-		return -ENOMEM;
+		return ret;
 
 	s = kzalloc_obj(struct loongarch_pch_pic);
 	if (!s)
-- 
2.43.0

[PATCH v3 3/3] LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

KVM_DEV_LOONGARCH_PCH_PIC_CTRL_INIT has no guard against repeated
invocation: every call overwrites pch_pic_base and registers the same
kvm_io_device on the MMIO bus at the new address, while
kvm_pch_pic_destroy() unregisters only one bus range.  After a repeated
init, MMIO to the stale ranges computes its register offset against the
new base and silently reads 0 / drops writes, and the leftover bus
entries persist until the VM is destroyed.

Reject repeated initialization with -EEXIST, using the initialized
state of the kvm_io_device as the indicator.  The MMIO base is only
committed after a successful bus registration, and the real
registration error is propagated instead of being replaced with
-EFAULT.

Fixes: d206d9514873 ("LoongArch: KVM: Add PCHPIC user mode read and write functions")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 arch/loongarch/kvm/intc/pch_pic.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
index 51e4a6a39dc0..7979466de729 100644
--- a/arch/loongarch/kvm/intc/pch_pic.c
+++ b/arch/loongarch/kvm/intc/pch_pic.c
@@ -281,16 +281,22 @@ static int kvm_pch_pic_init(struct kvm_device *dev, u64 addr)
 	struct kvm_io_device *device;
 	struct loongarch_pch_pic *s = dev->kvm->arch.pch_pic;
 
-	s->pch_pic_base = addr;
 	device = &s->device;
+	mutex_lock(&kvm->slots_lock);
+	if (s->device.ops) {
+		ret = -EEXIST;
+		goto out;
+	}
 	/* init device by pch pic writing and reading ops */
 	kvm_iodevice_init(device, &kvm_pch_pic_ops);
-	mutex_lock(&kvm->slots_lock);
 	/* register pch pic device */
 	ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, addr, PCH_PIC_SIZE, device);
+	if (!ret)
+		s->pch_pic_base = addr;
+out:
 	mutex_unlock(&kvm->slots_lock);
 
-	return (ret < 0) ? -EFAULT : 0;
+	return ret;
 }
 
 /* used by user space to get or set pch pic registers */
-- 
2.43.0

Re: [PATCH v3 1/3] LoongArch: KVM: Clear device pointer in irqchip destroy callbacks

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [High] kvm: UAF window in dmsintc due to kfree before pointer clear
- [High] kvm: TOCTOU UAF and NULL deref in lockless IRQ injection
- [High] kvm: loongarch: unsynchronized device teardown leads to NULL pointer dereference in irq injection
--

commit adcfcba3d5e2b9e1058d8d66cd600edc9fa04efd
Author: Tao Cui <cuitao@kylinos.cn>

LoongArch: KVM: Clear device pointer in irqchip destroy callbacks

This commit aims to fix a dangling pointer vulnerability by explicitly
clearing device pointers in the destroy callbacks for LoongArch KVM irqchip
devices.

> diff --git a/arch/loongarch/kvm/intc/dmsintc.c b/arch/loongarch/kvm/intc/dmsintc.c
> index bb7285c49df3a..4bd98b888e3f1 100644
> --- a/arch/loongarch/kvm/intc/dmsintc.c
> +++ b/arch/loongarch/kvm/intc/dmsintc.c
[ ... ]
> @@ -166,6 +166,7 @@ static void kvm_dmsintc_destroy(struct kvm_device *dev)
>  		return;
>  
>  	kfree(dev->kvm->arch.dmsintc);
> +	dev->kvm->arch.dmsintc = NULL;

[Severity: High]
Since the pointer is explicitly freed before it is set to NULL, does this
leave a race window for concurrent lockless readers?

If anon_inode_getfd() fails during device creation, this destroy callback
runs while the VM is still active. A concurrent interrupt injection could
read the pointer right after the kfree() but before it is cleared to NULL,
leading to a use-after-free.

>  	kfree(dev);
>  }
>  

[ ... ]

> diff --git a/arch/loongarch/kvm/intc/eiointc.c b/arch/loongarch/kvm/intc/eiointc.c
> index 84d84bd432d74..9a8498c5deb9d 100644
> --- a/arch/loongarch/kvm/intc/eiointc.c
> +++ b/arch/loongarch/kvm/intc/eiointc.c
[ ... ]
> @@ -675,6 +675,7 @@ static void kvm_eiointc_destroy(struct kvm_device *dev)
>  
>  	kvm = dev->kvm;
>  	eiointc = kvm->arch.eiointc;
> +	kvm->arch.eiointc = NULL;
>  	mutex_lock(&kvm->slots_lock);
>  	kvm_io_bus_unregister_dev(kvm, KVM_IOCSR_BUS, &eiointc->device);
>  	kvm_io_bus_unregister_dev(kvm, KVM_IOCSR_BUS, &eiointc->device_vext);
>  	mutex_unlock(&kvm->slots_lock);
>  	kfree(eiointc);

[Severity: High]
Could clearing the pointer and freeing the device here without SRCU
synchronization lead to a use-after-free or NULL pointer dereference in
lockless IRQ injection paths?

If a concurrent thread is injecting interrupts (e.g., via KVM_IRQ_LINE) while
the device is being destroyed, it drops kvm->irq_srcu and locklessly calls
pch_msi_set_irq() or similar helpers. If it evaluates
kvm_arch_irqchip_in_kernel() before the pointer is cleared, it might pass
the dangling eiointc pointer to eiointc_set_irq(), which then blindly
dereferences it. Without a call to synchronize_srcu(&kvm->irq_srcu) before
freeing, this appears to result in a use-after-free.

Similarly, if the injection path reads the pointer exactly after it is set
to NULL, it passes a NULL pointer to eiointc_set_irq(), which will crash
when calling spin_lock_irqsave(&s->lock, flags).

>  	kfree(dev);
>  }

[ ... ]

> diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
> index e7b77705c516a..5d046a1cab4e2 100644
> --- a/arch/loongarch/kvm/intc/pch_pic.c
> +++ b/arch/loongarch/kvm/intc/pch_pic.c
[ ... ]
> @@ -480,6 +480,7 @@ static void kvm_pch_pic_destroy(struct kvm_device *dev)
>  
>  	kvm = dev->kvm;
>  	s = kvm->arch.pch_pic;
> +	kvm->arch.pch_pic = NULL;
>  	/* unregister pch pic device and free it's memory */
>  	mutex_lock(&kvm->slots_lock);
>  	kvm_io_bus_unregister_dev(kvm, KVM_MMIO_BUS, &s->device);
>  	mutex_unlock(&kvm->slots_lock);
>  	kfree(s);

[Severity: High]
Does unsynchronized device teardown here lead to a similar NULL pointer
dereference in the IRQ injection path?

If KVM_IRQFD or KVM_IRQ_LINE is called concurrently, kvm_set_irq() looks up
the routing and calls kvm_set_pic_irq(). The helper unconditionally reads
kvm->arch.pch_pic and passes it to pch_pic_set_irq():

arch/loongarch/kvm/irqfd.c:kvm_set_pic_irq() {
        pch_pic_set_irq(kvm->arch.pch_pic, e->irqchip.pin, level);
        ...
}

If the pointer was just cleared to NULL by this destroy callback, it results
in a deterministic NULL pointer dereference when pch_pic_set_irq()
immediately calls spin_lock(&s->lock). Should there be synchronization
against concurrent IRQ routing here?

>  	kfree(dev);
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261014052933.723303-1-cui.tao@linux.dev?part=1

Re: [PATCH v3 3/3] LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

[Huacai Chen]

Hi, Tao,

On Wed, Oct 14, 2026 at 1:30 PM Tao Cui <cui.tao@linux.dev> wrote:
>
> From: Tao Cui <cuitao@kylinos.cn>
>
> KVM_DEV_LOONGARCH_PCH_PIC_CTRL_INIT has no guard against repeated
> invocation: every call overwrites pch_pic_base and registers the same
> kvm_io_device on the MMIO bus at the new address, while
> kvm_pch_pic_destroy() unregisters only one bus range.  After a repeated
> init, MMIO to the stale ranges computes its register offset against the
> new base and silently reads 0 / drops writes, and the leftover bus
> entries persist until the VM is destroyed.
>
> Reject repeated initialization with -EEXIST, using the initialized
> state of the kvm_io_device as the indicator.  The MMIO base is only
> committed after a successful bus registration, and the real
> registration error is propagated instead of being replaced with
> -EFAULT.
>
> Fixes: d206d9514873 ("LoongArch: KVM: Add PCHPIC user mode read and write functions")
> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
> ---
>  arch/loongarch/kvm/intc/pch_pic.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
> index 51e4a6a39dc0..7979466de729 100644
> --- a/arch/loongarch/kvm/intc/pch_pic.c
> +++ b/arch/loongarch/kvm/intc/pch_pic.c
> @@ -281,16 +281,22 @@ static int kvm_pch_pic_init(struct kvm_device *dev, u64 addr)
>         struct kvm_io_device *device;
>         struct loongarch_pch_pic *s = dev->kvm->arch.pch_pic;
>
> -       s->pch_pic_base = addr;
>         device = &s->device;
> +       mutex_lock(&kvm->slots_lock);
Why move the mutex_lock()?

Huacai

> +       if (s->device.ops) {
> +               ret = -EEXIST;
> +               goto out;
> +       }
>         /* init device by pch pic writing and reading ops */
>         kvm_iodevice_init(device, &kvm_pch_pic_ops);
> -       mutex_lock(&kvm->slots_lock);
>         /* register pch pic device */
>         ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, addr, PCH_PIC_SIZE, device);
> +       if (!ret)
> +               s->pch_pic_base = addr;
> +out:
>         mutex_unlock(&kvm->slots_lock);
>
> -       return (ret < 0) ? -EFAULT : 0;
> +       return ret;
>  }
>
>  /* used by user space to get or set pch pic registers */
> --
> 2.43.0
>

Re: [PATCH v3 3/3] LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

[Tao Cui]

Hi, Huacai

在 2026/10/14 15:37, Huacai Chen 写道:
> Hi, Tao,
> 
> On Wed, Oct 14, 2026 at 1:30 PM Tao Cui <cui.tao@linux.dev> wrote:
>>
>> From: Tao Cui <cuitao@kylinos.cn>
>>
>> KVM_DEV_LOONGARCH_PCH_PIC_CTRL_INIT has no guard against repeated
>> invocation: every call overwrites pch_pic_base and registers the same
>> kvm_io_device on the MMIO bus at the new address, while
>> kvm_pch_pic_destroy() unregisters only one bus range.  After a repeated
>> init, MMIO to the stale ranges computes its register offset against the
>> new base and silently reads 0 / drops writes, and the leftover bus
>> entries persist until the VM is destroyed.
>>
>> Reject repeated initialization with -EEXIST, using the initialized
>> state of the kvm_io_device as the indicator.  The MMIO base is only
>> committed after a successful bus registration, and the real
>> registration error is propagated instead of being replaced with
>> -EFAULT.
>>
>> Fixes: d206d9514873 ("LoongArch: KVM: Add PCHPIC user mode read and write functions")
>> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
>> ---
>>  arch/loongarch/kvm/intc/pch_pic.c | 12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
>> index 51e4a6a39dc0..7979466de729 100644
>> --- a/arch/loongarch/kvm/intc/pch_pic.c
>> +++ b/arch/loongarch/kvm/intc/pch_pic.c
>> @@ -281,16 +281,22 @@ static int kvm_pch_pic_init(struct kvm_device *dev, u64 addr)
>>         struct kvm_io_device *device;
>>         struct loongarch_pch_pic *s = dev->kvm->arch.pch_pic;
>>
>> -       s->pch_pic_base = addr;
>>         device = &s->device;
>> +       mutex_lock(&kvm->slots_lock);
> Why move the mutex_lock()?
> 

Thanks for the question.

The intent is to keep the repeated-init check mutual-excluded with the
bus registration.  The set_attr ioctl path holds no other lock, so with
the check outside slots_lock, two concurrent CTRL_INIT calls could both
see device.ops == NULL and both register the same device on the MMIO
bus.  Holding the lock across the check, the registration and the base
commit makes them exclusive.

That said, if you prefer the check before the lock, I can respin --
please let me know.

Thanks,
Tao

> Huacai
> 
>> +       if (s->device.ops) {
>> +               ret = -EEXIST;
>> +               goto out;
>> +       }
>>         /* init device by pch pic writing and reading ops */
>>         kvm_iodevice_init(device, &kvm_pch_pic_ops);
>> -       mutex_lock(&kvm->slots_lock);
>>         /* register pch pic device */
>>         ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, addr, PCH_PIC_SIZE, device);
>> +       if (!ret)
>> +               s->pch_pic_base = addr;
>> +out:
>>         mutex_unlock(&kvm->slots_lock);
>>
>> -       return (ret < 0) ? -EFAULT : 0;
>> +       return ret;
>>  }
>>
>>  /* used by user space to get or set pch pic registers */
>> --
>> 2.43.0
>>