linux-hardening - Re: [PATCH 1/2] mux: Turn 'mux' into a flexible array in 'struct mux

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Message-ID: <19d7ddce-f911-481e-ac89-bc942e40fbe1@suswa.mountain>
Date: Mon, 27 Nov 2023 11:29:55 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Peter Rosin <peda@...ntia.se>, Kees Cook <keescook@...omium.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH 1/2] mux: Turn 'mux' into a flexible array in 'struct
 mux_chip'

On Sun, Nov 26, 2023 at 09:08:11AM +0100, Christophe JAILLET wrote:
> The 'mux' array stored in 'struct mux_chip' can be changed into a flexible
> array.
> 
> This saves:
>    - a pointer in the structure
>    - an indirection when accessing the array
>    - some pointer arithmetic when computing and storing the address in
>      'mux'
> 
> It is also now possible to use __counted_by() and struct_size() for
> additional safety.
> 
> The address for the 'priv' memory is computed with mux_chip_priv(). It
> should work as good with a flexible array.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> The struct_size() goodies only work if sizeof_priv is 0. Adding an
> additional size_add() would make it safe in all cases but would make code
> less readable (IMHO).

Once people start using size_add() then we'll get used to reading it.

The controllers value comes from device tree.  For example, in
mux_mmio_probe().

	ret = of_property_count_u32_elems(np, "mux-reg-masks");

I should make Smatch parse device trees.  So that it will know the
correct range for ret in that assignment.  Eventually, I will.

KTODO: make Smatch understand device tree values

regards,
dan carpenter