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

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Message-ID: <20200302173852.GB109022@kroah.com>
Date:   Mon, 2 Mar 2020 18:38:52 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     glider@...gle.com
Cc:     tkjos@...gle.com, keescook@...omium.org, arve@...roid.com,
        mingo@...hat.com, 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, Mar 02, 2020 at 02:04:29PM +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:
> 
> 	struct binder_transaction_data tr;
> 	if (copy_from_user(&tr, ptr, sizeof(tr)))
> 		return -EFAULT;
> 
> In such cases enabling CONFIG_INIT_STACK_ALL leads to insertion of
> redundant locals initialization that the compiler fails to remove.
> To work around this problem till Clang can deal with it, we apply
> __no_initialize to local Binder structures.

I would like to see actual benchmark numbers showing this is
needed/useful otherwise it's going to just be random people adding this
marking to random places with no real reason.

thanks,

greg k-h