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Date: Wed, 29 Nov 2017 15:20:40 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: "Tobin C. Harding" <me@tobin.cc>
Cc: kernel-hardening@lists.openwall.com,
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Subject: Re: [PATCH V11 0/5] hash addresses printed with %p
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On Wed, 29 Nov 2017 13:05:00 +1100 "Tobin C. Harding" <me@tobin.cc> wrote:

> Currently there exist approximately 14 000 places in the Kernel where
> addresses are being printed using an unadorned %p. This potentially
> leaks sensitive information regarding the Kernel layout in memory. Many
> of these calls are stale, instead of fixing every call lets hash the
> address by default before printing. This will of course break some
> users, forcing code printing needed addresses to be updated. We can add
> a printk specifier for this purpose (%px) to give developers a clear
> upgrade path for breakages caused by applying this patch set.
> 
> The added advantage of hashing %p is that security is now opt-out, if
> you _really_ want the address you have to work a little harder and use
> %px.
> 
> The idea for creating the printk specifier %px to print the actual
> address was suggested by Kees Cook (see below for email threads by
> subject).

Maybe I'm being thick, but...  if we're rendering these addresses
unusable by hashing them, why not just print something like
"<obscured>" in their place?  That loses the uniqueness thing but I
wonder how valuable that is in practice?