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Date: Thu, 04 Aug 2016 14:47:07 +0200
From: Yann Droneaud <ydroneaud@...eya.com>
To: Jason Cooper <jason@...edaemon.net>, Kees Cook <keescook@...omium.org>,
Michael Ellerman <mpe@...erman.id.au>, "Roberts, William C"
<william.c.roberts@...el.com>
Cc: Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
kernel-hardening <kernel-hardening@...ts.openwall.com>, Russell King - ARM
Linux <linux@....linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>,
Theodore Ts'o <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
gregkh@...uxfoundation.org, Catalin Marinas <catalin.marinas@....com>, Will
Deacon <will.deacon@....com>, Ralf Baechle <ralf@...ux-mips.org>,
benh@...nel.crashing.org, paulus@...ba.org, "David S. Miller"
<davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
<mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
viro@...iv.linux.org.uk, Nick Kralevich <nnk@...gle.com>, Jeffrey Vander
Stoep <jeffv@...gle.com>, Daniel Cashman <dcashman@...roid.com>
Subject: Re: [PATCH v3 1/7] random: Simplify API for random address requests
Hi,
Le mercredi 03 août 2016 à 23:39 +0000, Jason Cooper a écrit :
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 0158d3bff7e5..61cb434e3bea 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1840,6 +1840,39 @@ randomize_range(unsigned long start, unsigned
> long end, unsigned long len)
> return PAGE_ALIGN(get_random_int() % range + start);
> }
>
> +/**
> + * randomize_page - Generate a random, page aligned address
> + * @start: The smallest acceptable address the caller will
> take.
> + * @range: The size of the area, starting at @start, within
> which the
> + * random address must fall.
> + *
> + * If @start + @range would overflow, @range is capped.
> + *
> + * NOTE: Historical use of randomize_range, which this replaces,
> presumed that
> + * @start was already page aligned. We now align it regardless.
> + *
> + * Return: A page aligned address within [start, start + range). On
> error,
> + * @start is returned.
> + */
> +unsigned long
> +randomize_page(unsigned long start, unsigned long range)
> +{
To prevent an underflow if start is not page aligned (but will one
would ever use a non aligned start address *and* range ? ...)
if (range < PAGE_SIZE)
return start;
> + if (!PAGE_ALIGNED(start)) {
> + range -= PAGE_ALIGN(start) - start;
> + start = PAGE_ALIGN(start);
> + }
> +
> + if (start > ULONG_MAX - range)
> + range = ULONG_MAX - start;
> +
> + range >>= PAGE_SHIFT;
> +
> + if (range == 0)
> + return start;
> +
> + return start + (get_random_long() % range << PAGE_SHIFT);
> +}
> +
> /* Interface for in-kernel drivers of true hardware RNGs.
> * Those devices may produce endless random bits and will be
> throttled
> * when our pool is full.
>
Regards.
--
Yann Droneaud
OPTEYA
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