From: Julia Lawall <julia.lawall@inria.fr>
To: Kees Cook <keescook@chromium.org>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
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Subject: Re: [PATCH v4 2/6] treewide: use prandom_u32_max() when possible
Date: Sat, 8 Oct 2022 09:33:08 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.22.394.2210080925390.2928@hadrien> (raw)
In-Reply-To: <53DD0148-ED15-4294-8496-9E4B4C7AD061@chromium.org>
> >> @minus_one@
> >> expression FULL;
> >> @@
> >>
> >> - (get_random_int() & ((FULL) - 1)
> >> + prandom_u32_max(FULL)
> >
> >Ahh, well, okay, this is the example I mentioned above. Only works if
> >FULL is saturated. Any clever way to get coccinelle to prove that? Can
> >it look at the value of constants?
>
> I'm not sure if Cocci will do that without a lot of work. The literals trick I used below would need a lot of fanciness. :)
If FULL is an arbitrary expression, it would not be easy to automate. If
it is a constant then you can use python/ocaml to analyze its value. But
if it's a #define constant then you would need a previous rule to match the
#define and find that value.
For LITERAL, I think you could just do constant int LITERAL; for the
metavariable declaration.
julia
next prev parent reply other threads:[~2022-10-08 7:34 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-08 3:50 [PATCH v4 2/6] treewide: use prandom_u32_max() when possible Kees Cook
2022-10-08 7:33 ` Julia Lawall [this message]
2022-10-08 18:16 ` Andy Shevchenko
-- strict thread matches above, loose matches on Subject: below --
2022-10-07 18:01 [PATCH v4 0/6] treewide cleanup of random integer usage Jason A. Donenfeld
2022-10-07 18:01 ` [PATCH v4 2/6] treewide: use prandom_u32_max() when possible Jason A. Donenfeld
2022-10-07 21:17 ` Darrick J. Wong
2022-10-08 1:28 ` Jason A. Donenfeld
2022-10-07 22:47 ` Kees Cook
2022-10-08 2:21 ` Jason A. Donenfeld
2022-10-08 3:21 ` Jason A. Donenfeld
2022-10-08 22:08 ` David Laight
2022-10-08 22:19 ` Jason A. Donenfeld
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