Re: [PATCH V8 0/2] printk: hash addresses printed with %p

[Sergey Senozhatsky]

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?

	-ss