On Thu, Aug 23, 2018 at 3:00 PM, Julia Lawall <julia.law...@lip6.fr> wrote:
>
>
> On Thu, 23 Aug 2018, Kees Cook wrote:
>
>> On Thu, Aug 23, 2018 at 2:48 PM, Joe Perches <j...@perches.com> wrote:
>> > Forwarding a question about coccinelle and isomorphisms from Kees Cook
>> >
>> > ---------- Forwarded message ----------
>> > From: Kees Cook <keesc...@chromium.org>
>> > To: "Gustavo A. R. Silva" <gust...@embeddedor.com>
>> > Cc: Alessandro Zummo <a.zu...@towertech.it>, Alexandre Belloni
>> > <alexandre.bell...@bootlin.com>, Maxime Ripard
>> > <maxime.rip...@bootlin.com>, Chen-Yu Tsai <w...@csie.org>,
>> > linux-...@vger.kernel.org, linux-arm-kernel
>> > <linux-arm-ker...@lists.infradead.org>, LKML <linux-ker...@vger.kernel.org>
>> > Bcc:
>> > Date: Thu, 23 Aug 2018 13:56:35 -0700
>> > Subject: Re: [PATCH] rtc: sun6i: Use struct_size() in kzalloc()
>> > On Thu, Aug 23, 2018 at 11:51 AM, Gustavo A. R. Silva
>> > <gust...@embeddedor.com> wrote:
>> >> One of the more common cases of allocation size calculations is finding
>> >> the size of a structure that has a zero-sized array at the end, along
>> >> with memory for some number of elements for that array. For example:
>> >>
>> >> struct foo {
>> >> int stuff;
>> >> void *entry[];
>> >> };
>> >>
>> >> instance = kzalloc(sizeof(struct foo) + sizeof(void *) * count,
>> >> GFP_KERNEL);
>> >>
>> >> Instead of leaving these open-coded and prone to type mistakes, we can
>> >> now use the new struct_size() helper:
>> >>
>> >> instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);
>> >>
>> >> Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com>
>> >> ---
>> >> drivers/rtc/rtc-sun6i.c | 3 +--
>> >> 1 file changed, 1 insertion(+), 2 deletions(-)
>> >>
>> >> diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c
>> >> index 2cd5a7b..fe07310 100644
>> >> --- a/drivers/rtc/rtc-sun6i.c
>> >> +++ b/drivers/rtc/rtc-sun6i.c
>> >> @@ -199,8 +199,7 @@ static void __init sun6i_rtc_clk_init(struct
>> >> device_node *node)
>> >> if (!rtc)
>> >> return;
>> >>
>> >> - clk_data = kzalloc(sizeof(*clk_data) + (sizeof(*clk_data->hws) *
>> >> 2),
>> >> - GFP_KERNEL);
>> >> + clk_data = kzalloc(struct_size(clk_data, hws, 2), GFP_KERNEL);
>> >> if (!clk_data) {
>> >> kfree(rtc);
>> >> return;
>> >
>> > This looks like entirely correct to me, but I'm surprised the
>> > Coccinelle script didn't discover this. I guess the isomorphisms don't
>> > cover the parenthesis?
>>
>> I had this:
>>
>> @@
>> identifier alloc =~
>> "kmalloc|kzalloc|kmalloc_node|kzalloc_node|vmalloc|vzalloc|kvmalloc|kvzalloc";
>> identifier VAR, ELEMENT;
>> expression COUNT;
>> @@
>>
>> - alloc(sizeof(*VAR) + COUNT * sizeof(*VAR->ELEMENT)
>> + alloc(struct_size(VAR, ELEMENT, COUNT)
>> , ...)
>>
>> But I needed to explicitly change the rule to:
>>
>> (
>> - alloc(sizeof(*VAR) + COUNT * sizeof(*VAR->ELEMENT)
>> + alloc(struct_size(VAR, ELEMENT, COUNT)
>> , ...)
>> |
>> - alloc(sizeof(*VAR) + (COUNT * sizeof(*VAR->ELEMENT))
>> + alloc(struct_size(VAR, ELEMENT, COUNT)
>> , ...)
>> )
>>
>> to add the ()s. I would expect arithmetic commutative expressions to
>> match? But I had to add parens?
>
> Isomorphisms don't add parens. They only remove them. If they added
> them, you would end up with the possibility of having them everywhere, in
> all permutations, which would be slow and useless.
Would a rule for:
a + (b * c)
match:
a + b * c
?
-Kees
--
Kees Cook
Pixel Security
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