linux-kernel - Re: x86-ksysfs: Use kmalloc_array() in create_setup_data

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Date:   Wed, 7 Sep 2016 10:01:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Joe Perches <joe@...ches.com>
Cc:     SF Markus Elfring <elfring@...rs.sourceforge.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>, Dave Young <dyoung@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Matt Fleming <matt.fleming@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        Julia Lawall <julia.lawall@...6.fr>
Subject: Re: x86-ksysfs: Use kmalloc_array() in create_setup_data_nodes()

On Wed, Sep 7, 2016 at 9:37 AM, Joe Perches <joe@...ches.com> wrote:
> On Wed, 2016-09-07 at 09:23 -0700, Kees Cook wrote:
>> Fixing these kmalloc calls would be a nice thing to clean up
>> everywhere.
>
> Dubious as gcc cannot currently optimize known small fixed size
> allocations with alloc_array and will always perform the
> multiplication.

Oh, that's sad. Is it not able to tell what the types are to basic
overflow validation? Could we help gcc in some way?

> Also the style of sizeof(*ptr) is not always as clear, obvious
> nor as easy to grep as sizeof(type).

I've always been on the fence about this (I like being able to see
destination:thing, sizeof(*thing) for easy scanning), but having the
type right there can be easier for text searches.

-Kees

-- 
Kees Cook
Nexus Security