linux-kernel - Re: [PATCH v2 2/3] binder: do not initialize locals passed to copy_from

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Date:   Mon, 02 Mar 2020 05:09:58 -0800
From:   Joe Perches <joe@...ches.com>
To:     glider@...gle.com, tkjos@...gle.com, keescook@...omium.org,
        gregkh@...uxfoundation.org, arve@...roid.com, mingo@...hat.com
Cc:     dvyukov@...gle.com, jannh@...gle.com, devel@...verdev.osuosl.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] binder: do not initialize locals passed to
 copy_from_user()

On Mon, 2020-03-02 at 14:04 +0100, glider@...gle.com wrote:
> Certain copy_from_user() invocations in binder.c are known to
> unconditionally initialize locals before their first use, like e.g. in
> the following case:
[]
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
[]
> @@ -3788,7 +3788,7 @@ static int binder_thread_write(struct binder_proc *proc,
>  
>  		case BC_TRANSACTION_SG:
>  		case BC_REPLY_SG: {
> -			struct binder_transaction_data_sg tr;
> +			struct binder_transaction_data_sg tr __no_initialize;
>  
>  			if (copy_from_user(&tr, ptr, sizeof(tr)))

I fail to see any value in marking tr with __no_initialize
when it's immediately written to by copy_from_user.

>  				return -EFAULT;
> @@ -3799,7 +3799,7 @@ static int binder_thread_write(struct binder_proc *proc,
>  		}
>  		case BC_TRANSACTION:
>  		case BC_REPLY: {
> -			struct binder_transaction_data tr;
> +			struct binder_transaction_data tr __no_initialize;
>  
>  			if (copy_from_user(&tr, ptr, sizeof(tr)))

etc...