linux-kernel - Re: [PATCH] ELF: implement AT

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Message-ID: <20081003051543.GQ10632@outflux.net>
Date:	Thu, 2 Oct 2008 22:15:43 -0700
From:	Kees Cook <kees.cook@...onical.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Jakub Jelinek <jakub@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>, libc-alpha@...rceware.org
Subject: Re: [PATCH] ELF: implement AT_RANDOM for future glibc use

On Thu, Oct 02, 2008 at 05:52:58PM -0700, Roland McGrath wrote:
> I think the safe available AT_* values to use are 25, 26.

Out of curiosity, why are there gaps?  I figure I can include some
comments in that header to explain the gaps for future AT_* creations.

> I would configure the size in bytes.  Ulrich suggested it be 16 bytes on
> both 32-bit and 64-bit machines.

I was trying to make the size compile-time static so I could avoid
kmalloc'ing a buffer for get_random_bytes().  But maybe avoid that isn't
sensible?

As for 16 bytes on both 32bit and 64bit, I was aiming to have 4
pointer-sized random values.  16 works for 32bit, but I was hoping to
have 32 on 64bit.  Perhaps I am over-estimating?

-Kees

-- 
Kees Cook
Ubuntu Security Team
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