diff mbox series

[QEMU,v4,07/13] softmmu/memory: enable automatic deallocation of memory regions

Message ID 20230831093252.2461282-8-ray.huang@amd.com (mailing list archive)
State Superseded
Headers show
Series Support blob memory and venus on qemu | expand

Commit Message

Huang Rui Aug. 31, 2023, 9:32 a.m. UTC 
From: Xenia Ragiadakou <xenia.ragiadakou@amd.com>

When the memory region has a different life-cycle from that of her parent,
could be automatically released, once has been unparent and once all of her
references have gone away, via the object's free callback.

However, currently, references to the memory region are held by its owner
without first incrementing the memory region object's reference count.
As a result, the automatic deallocation of the object, not taking into
account those references, results in use-after-free memory corruption.

This patch increases the reference count of the memory region object on
each memory_region_ref() and decreases it on each memory_region_unref().

Signed-off-by: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
Signed-off-by: Huang Rui <ray.huang@amd.com>
---

New patch

 softmmu/memory.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

Comments

Akihiko Odaki Aug. 31, 2023, 10:10 a.m. UTC | #1 
On 2023/08/31 18:32, Huang Rui wrote:
> From: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
> 
> When the memory region has a different life-cycle from that of her parent,
> could be automatically released, once has been unparent and once all of her
> references have gone away, via the object's free callback.
> 
> However, currently, references to the memory region are held by its owner
> without first incrementing the memory region object's reference count.
> As a result, the automatic deallocation of the object, not taking into
> account those references, results in use-after-free memory corruption.
> 
> This patch increases the reference count of the memory region object on
> each memory_region_ref() and decreases it on each memory_region_unref().
> 
> Signed-off-by: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
> Signed-off-by: Huang Rui <ray.huang@amd.com>
> ---
> 
> New patch
> 
>   softmmu/memory.c | 19 +++++++++++++++++--
>   1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index 7d9494ce70..0fdd5eebf9 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -1797,6 +1797,15 @@ Object *memory_region_owner(MemoryRegion *mr)
>   
>   void memory_region_ref(MemoryRegion *mr)
>   {
> +    if (!mr) {
> +        return;
> +    }
> +
> +    /* Obtain a reference to prevent the memory region object
> +     * from being released under our feet.
> +     */
> +    object_ref(OBJECT(mr));
> +
>       /* MMIO callbacks most likely will access data that belongs
>        * to the owner, hence the need to ref/unref the owner whenever
>        * the memory region is in use.
> @@ -1807,16 +1816,22 @@ void memory_region_ref(MemoryRegion *mr)
>        * Memory regions without an owner are supposed to never go away;
>        * we do not ref/unref them because it slows down DMA sensibly.
>        */

The collapsed comment says:
 > The memory region is a child of its owner.  As long as the
 > owner doesn't call unparent itself on the memory region,
 > ref-ing the owner will also keep the memory region alive.
 > Memory regions without an owner are supposed to never go away;
 > we do not ref/unref them because it slows down DMA sensibly.

It contradicts with this patch.

> -    if (mr && mr->owner) {
> +    if (mr->owner) {
>           object_ref(mr->owner);
>       }
>   }
>   
>   void memory_region_unref(MemoryRegion *mr)
>   {
> -    if (mr && mr->owner) {
> +    if (!mr) {
> +        return;
> +    }
> +
> +    if (mr->owner) {
>           object_unref(mr->owner);
>       }
> +
> +    object_unref(OBJECT(mr));
>   }
>   
>   uint64_t memory_region_size(MemoryRegion *mr)
Huang Rui Sept. 5, 2023, 9:07 a.m. UTC | #2 
On Thu, Aug 31, 2023 at 06:10:08PM +0800, Akihiko Odaki wrote:
> On 2023/08/31 18:32, Huang Rui wrote:
> > From: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
> > 
> > When the memory region has a different life-cycle from that of her parent,
> > could be automatically released, once has been unparent and once all of her
> > references have gone away, via the object's free callback.
> > 
> > However, currently, references to the memory region are held by its owner
> > without first incrementing the memory region object's reference count.
> > As a result, the automatic deallocation of the object, not taking into
> > account those references, results in use-after-free memory corruption.
> > 
> > This patch increases the reference count of the memory region object on
> > each memory_region_ref() and decreases it on each memory_region_unref().
> > 
> > Signed-off-by: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
> > Signed-off-by: Huang Rui <ray.huang@amd.com>
> > ---
> > 
> > New patch
> > 
> >   softmmu/memory.c | 19 +++++++++++++++++--
> >   1 file changed, 17 insertions(+), 2 deletions(-)
> > 
> > diff --git a/softmmu/memory.c b/softmmu/memory.c
> > index 7d9494ce70..0fdd5eebf9 100644
> > --- a/softmmu/memory.c
> > +++ b/softmmu/memory.c
> > @@ -1797,6 +1797,15 @@ Object *memory_region_owner(MemoryRegion *mr)
> >   
> >   void memory_region_ref(MemoryRegion *mr)
> >   {
> > +    if (!mr) {
> > +        return;
> > +    }
> > +
> > +    /* Obtain a reference to prevent the memory region object
> > +     * from being released under our feet.
> > +     */
> > +    object_ref(OBJECT(mr));
> > +
> >       /* MMIO callbacks most likely will access data that belongs
> >        * to the owner, hence the need to ref/unref the owner whenever
> >        * the memory region is in use.
> > @@ -1807,16 +1816,22 @@ void memory_region_ref(MemoryRegion *mr)
> >        * Memory regions without an owner are supposed to never go away;
> >        * we do not ref/unref them because it slows down DMA sensibly.
> >        */
> 
> The collapsed comment says:
>  > The memory region is a child of its owner.  As long as the
>  > owner doesn't call unparent itself on the memory region,
>  > ref-ing the owner will also keep the memory region alive.
>  > Memory regions without an owner are supposed to never go away;
>  > we do not ref/unref them because it slows down DMA sensibly.
> 
> It contradicts with this patch.

The reason that we modify it is because we would like to address the memory
leak issue in the original codes. Please see below, we find the memory
region will be crashed once we free(unref) the simple resource, because the
region will be freed in object_finalize() after unparent and the ref count
is to 0. Then the VM will be crashed with this.

In virgl_cmd_resource_map_blob():
    memory_region_init_ram_device_ptr(res->region, OBJECT(g), NULL, size, data);
    OBJECT(res->region)->free = g_free;
    memory_region_add_subregion(&b->hostmem, mblob.offset, res->region);
    memory_region_set_enabled(res->region, true);

In virtio_gpu_virgl_resource_unmap():
    memory_region_set_enabled(res->region, false);
    memory_region_del_subregion(&b->hostmem, res->region);
    object_unparent(OBJECT(res->region));
    res->region = NULL;

I spent a bit more time to understand your point, do you want me to update
corresponding comments or you have some concern about this change?

Thanks,
Ray

> 
> > -    if (mr && mr->owner) {
> > +    if (mr->owner) {
> >           object_ref(mr->owner);
> >       }
> >   }
> >   
> >   void memory_region_unref(MemoryRegion *mr)
> >   {
> > -    if (mr && mr->owner) {
> > +    if (!mr) {
> > +        return;
> > +    }
> > +
> > +    if (mr->owner) {
> >           object_unref(mr->owner);
> >       }
> > +
> > +    object_unref(OBJECT(mr));
> >   }
> >   
> >   uint64_t memory_region_size(MemoryRegion *mr)
Akihiko Odaki Sept. 5, 2023, 9:17 a.m. UTC | #3 
On 2023/09/05 18:07, Huang Rui wrote:
> On Thu, Aug 31, 2023 at 06:10:08PM +0800, Akihiko Odaki wrote:
>> On 2023/08/31 18:32, Huang Rui wrote:
>>> From: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
>>>
>>> When the memory region has a different life-cycle from that of her parent,
>>> could be automatically released, once has been unparent and once all of her
>>> references have gone away, via the object's free callback.
>>>
>>> However, currently, references to the memory region are held by its owner
>>> without first incrementing the memory region object's reference count.
>>> As a result, the automatic deallocation of the object, not taking into
>>> account those references, results in use-after-free memory corruption.
>>>
>>> This patch increases the reference count of the memory region object on
>>> each memory_region_ref() and decreases it on each memory_region_unref().
>>>
>>> Signed-off-by: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
>>> Signed-off-by: Huang Rui <ray.huang@amd.com>
>>> ---
>>>
>>> New patch
>>>
>>>    softmmu/memory.c | 19 +++++++++++++++++--
>>>    1 file changed, 17 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/softmmu/memory.c b/softmmu/memory.c
>>> index 7d9494ce70..0fdd5eebf9 100644
>>> --- a/softmmu/memory.c
>>> +++ b/softmmu/memory.c
>>> @@ -1797,6 +1797,15 @@ Object *memory_region_owner(MemoryRegion *mr)
>>>    
>>>    void memory_region_ref(MemoryRegion *mr)
>>>    {
>>> +    if (!mr) {
>>> +        return;
>>> +    }
>>> +
>>> +    /* Obtain a reference to prevent the memory region object
>>> +     * from being released under our feet.
>>> +     */
>>> +    object_ref(OBJECT(mr));
>>> +
>>>        /* MMIO callbacks most likely will access data that belongs
>>>         * to the owner, hence the need to ref/unref the owner whenever
>>>         * the memory region is in use.
>>> @@ -1807,16 +1816,22 @@ void memory_region_ref(MemoryRegion *mr)
>>>         * Memory regions without an owner are supposed to never go away;
>>>         * we do not ref/unref them because it slows down DMA sensibly.
>>>         */
>>
>> The collapsed comment says:
>>   > The memory region is a child of its owner.  As long as the
>>   > owner doesn't call unparent itself on the memory region,
>>   > ref-ing the owner will also keep the memory region alive.
>>   > Memory regions without an owner are supposed to never go away;
>>   > we do not ref/unref them because it slows down DMA sensibly.
>>
>> It contradicts with this patch.
> 
> The reason that we modify it is because we would like to address the memory
> leak issue in the original codes. Please see below, we find the memory
> region will be crashed once we free(unref) the simple resource, because the
> region will be freed in object_finalize() after unparent and the ref count
> is to 0. Then the VM will be crashed with this.
> 
> In virgl_cmd_resource_map_blob():
>      memory_region_init_ram_device_ptr(res->region, OBJECT(g), NULL, size, data);
>      OBJECT(res->region)->free = g_free;
>      memory_region_add_subregion(&b->hostmem, mblob.offset, res->region);
>      memory_region_set_enabled(res->region, true);
> 
> In virtio_gpu_virgl_resource_unmap():
>      memory_region_set_enabled(res->region, false);
>      memory_region_del_subregion(&b->hostmem, res->region);
>      object_unparent(OBJECT(res->region));
>      res->region = NULL;
> 
> I spent a bit more time to understand your point, do you want me to update
> corresponding comments or you have some concern about this change?

As the comment says ref-ing memory regions without an owner will slow 
down DMA, you should avoid that. More concretely, you should check 
mr->owner before doing object_ref(OBJECT(mr)).

Regards,
Akihiko Odaki
Huang Rui Sept. 5, 2023, 1:29 p.m. UTC | #4 
On Tue, Sep 05, 2023 at 05:17:32PM +0800, Akihiko Odaki wrote:
> On 2023/09/05 18:07, Huang Rui wrote:
> > On Thu, Aug 31, 2023 at 06:10:08PM +0800, Akihiko Odaki wrote:
> >> On 2023/08/31 18:32, Huang Rui wrote:
> >>> From: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
> >>>
> >>> When the memory region has a different life-cycle from that of her parent,
> >>> could be automatically released, once has been unparent and once all of her
> >>> references have gone away, via the object's free callback.
> >>>
> >>> However, currently, references to the memory region are held by its owner
> >>> without first incrementing the memory region object's reference count.
> >>> As a result, the automatic deallocation of the object, not taking into
> >>> account those references, results in use-after-free memory corruption.
> >>>
> >>> This patch increases the reference count of the memory region object on
> >>> each memory_region_ref() and decreases it on each memory_region_unref().
> >>>
> >>> Signed-off-by: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
> >>> Signed-off-by: Huang Rui <ray.huang@amd.com>
> >>> ---
> >>>
> >>> New patch
> >>>
> >>>    softmmu/memory.c | 19 +++++++++++++++++--
> >>>    1 file changed, 17 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/softmmu/memory.c b/softmmu/memory.c
> >>> index 7d9494ce70..0fdd5eebf9 100644
> >>> --- a/softmmu/memory.c
> >>> +++ b/softmmu/memory.c
> >>> @@ -1797,6 +1797,15 @@ Object *memory_region_owner(MemoryRegion *mr)
> >>>    
> >>>    void memory_region_ref(MemoryRegion *mr)
> >>>    {
> >>> +    if (!mr) {
> >>> +        return;
> >>> +    }
> >>> +
> >>> +    /* Obtain a reference to prevent the memory region object
> >>> +     * from being released under our feet.
> >>> +     */
> >>> +    object_ref(OBJECT(mr));
> >>> +
> >>>        /* MMIO callbacks most likely will access data that belongs
> >>>         * to the owner, hence the need to ref/unref the owner whenever
> >>>         * the memory region is in use.
> >>> @@ -1807,16 +1816,22 @@ void memory_region_ref(MemoryRegion *mr)
> >>>         * Memory regions without an owner are supposed to never go away;
> >>>         * we do not ref/unref them because it slows down DMA sensibly.
> >>>         */
> >>
> >> The collapsed comment says:
> >>   > The memory region is a child of its owner.  As long as the
> >>   > owner doesn't call unparent itself on the memory region,
> >>   > ref-ing the owner will also keep the memory region alive.
> >>   > Memory regions without an owner are supposed to never go away;
> >>   > we do not ref/unref them because it slows down DMA sensibly.
> >>
> >> It contradicts with this patch.
> > 
> > The reason that we modify it is because we would like to address the memory
> > leak issue in the original codes. Please see below, we find the memory
> > region will be crashed once we free(unref) the simple resource, because the
> > region will be freed in object_finalize() after unparent and the ref count
> > is to 0. Then the VM will be crashed with this.
> > 
> > In virgl_cmd_resource_map_blob():
> >      memory_region_init_ram_device_ptr(res->region, OBJECT(g), NULL, size, data);
> >      OBJECT(res->region)->free = g_free;
> >      memory_region_add_subregion(&b->hostmem, mblob.offset, res->region);
> >      memory_region_set_enabled(res->region, true);
> > 
> > In virtio_gpu_virgl_resource_unmap():
> >      memory_region_set_enabled(res->region, false);
> >      memory_region_del_subregion(&b->hostmem, res->region);
> >      object_unparent(OBJECT(res->region));
> >      res->region = NULL;
> > 
> > I spent a bit more time to understand your point, do you want me to update
> > corresponding comments or you have some concern about this change?
> 
> As the comment says ref-ing memory regions without an owner will slow 
> down DMA, you should avoid that. More concretely, you should check 
> mr->owner before doing object_ref(OBJECT(mr)).
> 

I get it, thanks to point this exactly. Will update it in V5.

Thanks,
Ray
diff mbox series

Patch

diff --git a/softmmu/memory.c b/softmmu/memory.c
index 7d9494ce70..0fdd5eebf9 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1797,6 +1797,15 @@  Object *memory_region_owner(MemoryRegion *mr)
 
 void memory_region_ref(MemoryRegion *mr)
 {
+    if (!mr) {
+        return;
+    }
+
+    /* Obtain a reference to prevent the memory region object
+     * from being released under our feet.
+     */
+    object_ref(OBJECT(mr));
+
     /* MMIO callbacks most likely will access data that belongs
      * to the owner, hence the need to ref/unref the owner whenever
      * the memory region is in use.
@@ -1807,16 +1816,22 @@  void memory_region_ref(MemoryRegion *mr)
      * Memory regions without an owner are supposed to never go away;
      * we do not ref/unref them because it slows down DMA sensibly.
      */
-    if (mr && mr->owner) {
+    if (mr->owner) {
         object_ref(mr->owner);
     }
 }
 
 void memory_region_unref(MemoryRegion *mr)
 {
-    if (mr && mr->owner) {
+    if (!mr) {
+        return;
+    }
+
+    if (mr->owner) {
         object_unref(mr->owner);
     }
+
+    object_unref(OBJECT(mr));
 }
 
 uint64_t memory_region_size(MemoryRegion *mr)