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Date: Fri, 27 Oct 2017 22:33:01 +0900
From: Sergey Senozhatsky <>
To: "Tobin C. Harding" <>
	"Jason A. Donenfeld" <>,
	Theodore Ts'o <>,
	Linus Torvalds <>,
	Kees Cook <>,
	Paolo Bonzini <>,
	Tycho Andersen <>,
	"Roberts, William C" <>,
	Tejun Heo <>,
	Jordan Glover <>,
	Greg KH <>,
	Petr Mladek <>, Joe Perches <>,
	Ian Campbell <>,
	Sergey Senozhatsky <>,
	Catalin Marinas <>,
	Will Deacon <>,
	Steven Rostedt <>,
	Chris Fries <>, Dave Weinstein <>,
	Daniel Micay <>,
	Djalal Harouni <>,
Subject: Re: [PATCH V8 0/2] printk: hash addresses printed with %p

On (10/26/17 13:53), Tobin C. Harding wrote:
> Currently there are many places in the kernel where addresses are being
> printed using an unadorned %p. Kernel pointers should be printed using
> %pK allowing some control via the kptr_restrict sysctl. Exposing
> addresses gives attackers sensitive information about the kernel layout
> in memory.
> We can reduce the attack surface by hashing all addresses printed with
> %p. This will of course break some users, forcing code printing needed
> addresses to be updated.
> With this version we include hashing of malformed specifiers also.
> Malformed specifiers include incomplete (e.g %pi) and also non-existent
> specifiers. checkpatch should warn for non-existent specifiers but
> AFAICT won't warn for incomplete specifiers.
> Here is the behaviour that this set implements.
> For kpt_restrict==0
> Randomness not ready:
>   printed with %p: 		(pointer)          # NOTE: with padding
> Valid pointer:
>   printed with %pK: 		deadbeefdeadbeef
>   printed with %p: 		0xdeadbeef
>   malformed specifier (eg %i):  0xdeadbeef
> NULL pointer:
>   printed with %pK: 		0000000000000000
>   printed with %p: 		(null)               # NOTE: no padding
>   malformed specifier (eg %i):  (null)

a quick question:
 do we care about cases when kernel pointers are printed with %x/%X and
 not with %p?


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