Re: [RFC c/r 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7

[Vasiliy Kulikov]

Hi Cyrill,

On Fri, Jan 27, 2012 at 21:53 +0400, Cyrill Gorcunov wrote:
> +/*
> + * We don't expose real in-memory order of objects for security
> + * reasons, still the comparision results should be suitable for
> + * sorting. Thus, we obfuscate kernel pointers values (using random
> + * cookies obtaned at early boot stage) and compare the production
> + * instead.
> + */
> +static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
> +
> +static long kptr_obfuscate(long v, int type)
> +{
> +	return (v ^ cookies[type][0]) * cookies[type][1];

AFACS, cookies is fully random value, is it possible that

((v1 ^ cookies[type][0]) * cookies[type][1] == (v2 ^ cookies[type][0]) * cookies[type][1]) &&
(v1 != v2)

for too round cookies[type][1]?

Thanks,

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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