[PATCH v2] kvm: Fix crash due to access uninitialized kvm_state

[PATCH v2] kvm: Fix crash due to access uninitialized kvm_state

[Gavin Shan]

Runs into core dump on arm64 and the backtrace extracted from the
core dump is shown as below. It's caused by accessing uninitialized
@kvm_state in kvm_flush_coalesced_mmio_buffer() due to commit 176d073029
("hw/arm/virt: Use machine_memory_devices_init()"), where the machine's
memory region is added earlier than before.

    main
    qemu_init
    configure_accelerators
    qemu_opts_foreach
    do_configure_accelerator
    accel_init_machine
    kvm_init
    virt_kvm_type
    virt_set_memmap
    machine_memory_devices_init
    memory_region_add_subregion
    memory_region_add_subregion_common
    memory_region_update_container_subregions
    memory_region_transaction_begin
    qemu_flush_coalesced_mmio_buffer
    kvm_flush_coalesced_mmio_buffer

Fix it by bailing early in kvm_flush_coalesced_mmio_buffer() on the
uninitialized @kvm_state. With this applied, no crash is observed on
arm64.

Fixes: 176d073029 ("hw/arm/virt: Use machine_memory_devices_init()")
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
v2: Bail early in kvm_flush_coalesced_mmio_buffer() on the uninitialized
    @kvm_state and improved changelog        (David/Peter)
---
 accel/kvm/kvm-all.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 373d876c05..7b3da8dc3a 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2812,7 +2812,7 @@ void kvm_flush_coalesced_mmio_buffer(void)
 {
     KVMState *s = kvm_state;
 
-    if (s->coalesced_flush_in_progress) {
+    if (!s || s->coalesced_flush_in_progress) {
         return;
     }
 
-- 
2.41.0

Re: [PATCH v2] kvm: Fix crash due to access uninitialized kvm_state

[David Hildenbrand]

On 31.07.23 14:59, Gavin Shan wrote:
> Runs into core dump on arm64 and the backtrace extracted from the
> core dump is shown as below. It's caused by accessing uninitialized
> @kvm_state in kvm_flush_coalesced_mmio_buffer() due to commit 176d073029
> ("hw/arm/virt: Use machine_memory_devices_init()"), where the machine's
> memory region is added earlier than before.
> 
>      main
>      qemu_init
>      configure_accelerators
>      qemu_opts_foreach
>      do_configure_accelerator
>      accel_init_machine
>      kvm_init
>      virt_kvm_type
>      virt_set_memmap
>      machine_memory_devices_init
>      memory_region_add_subregion
>      memory_region_add_subregion_common
>      memory_region_update_container_subregions
>      memory_region_transaction_begin
>      qemu_flush_coalesced_mmio_buffer
>      kvm_flush_coalesced_mmio_buffer
> 
> Fix it by bailing early in kvm_flush_coalesced_mmio_buffer() on the
> uninitialized @kvm_state. With this applied, no crash is observed on
> arm64.
> 
> Fixes: 176d073029 ("hw/arm/virt: Use machine_memory_devices_init()")
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
> v2: Bail early in kvm_flush_coalesced_mmio_buffer() on the uninitialized
>      @kvm_state and improved changelog        (David/Peter)
> ---
>   accel/kvm/kvm-all.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 373d876c05..7b3da8dc3a 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -2812,7 +2812,7 @@ void kvm_flush_coalesced_mmio_buffer(void)
>   {
>       KVMState *s = kvm_state;
>   
> -    if (s->coalesced_flush_in_progress) {
> +    if (!s || s->coalesced_flush_in_progress) {
>           return;
>       }
>   

Thanks Gavin!

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

Re: [PATCH v2] kvm: Fix crash due to access uninitialized kvm_state

[Peter Maydell]

On Mon, 31 Jul 2023 at 14:00, David Hildenbrand <david@redhat.com> wrote:
>
> On 31.07.23 14:59, Gavin Shan wrote:
> > Runs into core dump on arm64 and the backtrace extracted from the
> > core dump is shown as below. It's caused by accessing uninitialized
> > @kvm_state in kvm_flush_coalesced_mmio_buffer() due to commit 176d073029
> > ("hw/arm/virt: Use machine_memory_devices_init()"), where the machine's
> > memory region is added earlier than before.
> >
> >      main
> >      qemu_init
> >      configure_accelerators
> >      qemu_opts_foreach
> >      do_configure_accelerator
> >      accel_init_machine
> >      kvm_init
> >      virt_kvm_type
> >      virt_set_memmap
> >      machine_memory_devices_init
> >      memory_region_add_subregion
> >      memory_region_add_subregion_common
> >      memory_region_update_container_subregions
> >      memory_region_transaction_begin
> >      qemu_flush_coalesced_mmio_buffer
> >      kvm_flush_coalesced_mmio_buffer
> >
> > Fix it by bailing early in kvm_flush_coalesced_mmio_buffer() on the
> > uninitialized @kvm_state. With this applied, no crash is observed on
> > arm64.
> >
> > Fixes: 176d073029 ("hw/arm/virt: Use machine_memory_devices_init()")
> > Signed-off-by: Gavin Shan <gshan@redhat.com>
> > ---
> > v2: Bail early in kvm_flush_coalesced_mmio_buffer() on the uninitialized
> >      @kvm_state and improved changelog        (David/Peter)
> > ---
> >   accel/kvm/kvm-all.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> > index 373d876c05..7b3da8dc3a 100644
> > --- a/accel/kvm/kvm-all.c
> > +++ b/accel/kvm/kvm-all.c
> > @@ -2812,7 +2812,7 @@ void kvm_flush_coalesced_mmio_buffer(void)
> >   {
> >       KVMState *s = kvm_state;
> >
> > -    if (s->coalesced_flush_in_progress) {
> > +    if (!s || s->coalesced_flush_in_progress) {
> >           return;
> >       }
> >
>
> Thanks Gavin!
>
> Reviewed-by: David Hildenbrand <david@redhat.com>



Applied to target-arm.next, thanks.

-- PMM

Re: [PATCH v2] kvm: Fix crash due to access uninitialized kvm_state

[Philippe Mathieu-Daudé]

On 31/7/23 14:59, Gavin Shan wrote:
> Runs into core dump on arm64 and the backtrace extracted from the
> core dump is shown as below. It's caused by accessing uninitialized
> @kvm_state in kvm_flush_coalesced_mmio_buffer() due to commit 176d073029
> ("hw/arm/virt: Use machine_memory_devices_init()"), where the machine's
> memory region is added earlier than before.
> 
>      main
>      qemu_init
>      configure_accelerators
>      qemu_opts_foreach
>      do_configure_accelerator
>      accel_init_machine
>      kvm_init
>      virt_kvm_type
>      virt_set_memmap
>      machine_memory_devices_init
>      memory_region_add_subregion
>      memory_region_add_subregion_common
>      memory_region_update_container_subregions
>      memory_region_transaction_begin
>      qemu_flush_coalesced_mmio_buffer
>      kvm_flush_coalesced_mmio_buffer
> 
> Fix it by bailing early in kvm_flush_coalesced_mmio_buffer() on the
> uninitialized @kvm_state. With this applied, no crash is observed on
> arm64.
> 
> Fixes: 176d073029 ("hw/arm/virt: Use machine_memory_devices_init()")
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
> v2: Bail early in kvm_flush_coalesced_mmio_buffer() on the uninitialized
>      @kvm_state and improved changelog        (David/Peter)
> ---
>   accel/kvm/kvm-all.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>