linux-kernel - Re: [PATCH v2] binder: use buffer offsets in debug logs

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Message-ID: <Z-Go6qOLxT0ZfxyD@google.com>
Date: Mon, 24 Mar 2025 18:48:10 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: "Tiffany Y. Yang" <ynaffit@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Christian Brauner <brauner@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v2] binder: use buffer offsets in debug logs

On Mon, Mar 24, 2025 at 06:07:18PM +0000, Tiffany Y. Yang wrote:
> Identify buffer addresses using vma offsets instead of full user
> addresses in debug logs.
> 
> Signed-off-by: Tiffany Y. Yang <ynaffit@...gle.com>
> ---
>  drivers/android/binder.c | 31 ++++++++++++++++---------------
>  1 file changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index d1aa6d24450a..994ae205aa07 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -3261,20 +3261,20 @@ static void binder_transaction(struct binder_proc *proc,
>  
>  	if (reply)
>  		binder_debug(BINDER_DEBUG_TRANSACTION,
> -			     "%d:%d BC_REPLY %d -> %d:%d, data %016llx-%016llx size %lld-%lld-%lld\n",
> +			     "%d:%d BC_REPLY %d -> %d:%d, buffer offset %lx-%lx size %lld-%lld-%lld\n",
>  			     proc->pid, thread->pid, t->debug_id,
>  			     target_proc->pid, target_thread->pid,
> -			     (u64)tr->data.ptr.buffer,
> -			     (u64)tr->data.ptr.offsets,
> +			     (unsigned long)tr->data.ptr.buffer - proc->alloc.buffer,
> +			     (unsigned long)tr->data.ptr.offsets - proc->alloc.buffer,

These could be pointers to anywhere in user memory, not necessarily the
alloc->buffer. So there will be cases where this substraction doesn't
make sense. However, you are correct that we shouldn't log these addrs
so maybe just don't? wdyt?

>  			     (u64)tr->data_size, (u64)tr->offsets_size,
>  			     (u64)extra_buffers_size);
>  	else
>  		binder_debug(BINDER_DEBUG_TRANSACTION,
> -			     "%d:%d BC_TRANSACTION %d -> %d - node %d, data %016llx-%016llx size %lld-%lld-%lld\n",
> +			     "%d:%d BC_TRANSACTION %d -> %d - node %d, buffer offset %lx-%lx size %lld-%lld-%lld\n",
>  			     proc->pid, thread->pid, t->debug_id,
>  			     target_proc->pid, target_node->debug_id,
> -			     (u64)tr->data.ptr.buffer,
> -			     (u64)tr->data.ptr.offsets,
> +			     (unsigned long)tr->data.ptr.buffer - proc->alloc.buffer,
> +			     (unsigned long)tr->data.ptr.offsets - proc->alloc.buffer,
same here.

Regards,
--
Carlos Llamas