Re: [PATCH] Drivers: hv: vmbus: annotate struct vmbus_gpadl with __counted_by_ptr

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 9/23/26 16:23, Kees Cook wrote:
> On Wed, Sep 23, 2026 at 03:10:08PM +0900, Gustavo A. R. Silva wrote:
>>
>>
>> On 9/23/26 14:53, Bill Wendling wrote:
>>> Add the "__counted_by_ptr" attribute to the buffer field of "struct
>>> vmbus_gpadl". This allows compilers (GCC and Clang) to perform
>>> compile-time and runtime bounds-checking when KASAN is enabled, preventing
>>> potential out-of-bounds accesses to the GPADL buffer.
>>>
>>> The fields "buffer" and "size" of "struct vmbus_gpadl" are assigned
>>> exactly once, during GPADL establishment inside
>>> "__vmbus_establish_gpadl()" in "drivers/hv/channel.c".
>>>
>>> To ensure that the count field ("size") is initialized before the
>>> pointer field ("buffer") is assigned, we reorder the assignments in
>>> "__vmbus_establish_gpadl()" so that "gpadl->size" is written before
>>> "gpadl->buffer".
>>>
>>> Cc: codemender-patching+linux@google.com
>>> Assisted-by: LLM
>>> Signed-off-by: Bill Wendling <morbo@google.com>
>>> ---
>>>    drivers/hv/channel.c   | 2 +-
>>>    include/linux/hyperv.h | 2 +-
>>>    2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
>>> index 7e4cc6f55237..7042de2dd481 100644
>>> --- a/drivers/hv/channel.c
>>> +++ b/drivers/hv/channel.c
>>> @@ -548,8 +548,8 @@ static int __vmbus_establish_gpadl(struct vmbus_channel *channel,
>>>    	/* At this point, we received the gpadl created msg */
>>>    	gpadl->gpadl_handle = gpadlmsg->gpadl;
>>> -	gpadl->buffer = kbuffer;
>>>    	gpadl->size = size;
>>> +	gpadl->buffer = kbuffer;
>>
>> I think in some cases these subtle changes are worth a short but
>> informative comment saying that the _counter_ must be initialized
>> before the first reference to the pointer.
> 
> But that's only for dereferencing it... there's no ordering requirement

Ah yes, I got a bit carried away by the change itself.

> here at all (and I think swapping order is needless churn). Neither
> order is correct: only having them both set before dereferencing
> "buffer" is required.
Yes; maybe this is something the LLM should learn.

Thanks
-Gustavo