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

[Kees Cook <kees@kernel.org>]

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
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.


-- 
Kees Cook