linux-kernel - Re: [PATCH 26/26] x86, pkeys: Documentation

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Date:	Tue, 6 Oct 2015 16:28:05 -0700
From:	Dave Hansen <dave@...1.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Kees Cook <keescook@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 26/26] x86, pkeys: Documentation

On 10/03/2015 12:27 AM, Ingo Molnar wrote:
>  - I'd also suggest providing an initial value with the 'alloc' call. It's true 
>    that user-space can do this itself in assembly, OTOH there's no reason not to 
>    provide a C interface for this.

You mean an initial value for the rights register (PKRU), correct?

So init_val would be something like

	PKEY_DENY_ACCESS
	PKEY_DENY_WRITE

and it would refer only to the key that was allocated.

>  - Along similar considerations, also add a sys_pkey_query() system call to query 
>    the mapping of a specific pkey. (returns -EBADF or so if the key is not mapped
>    at the moment.) This too could be vDSO accelerated in the future.

Do you mean whether the key is being used on a mapping (VMA) or rather
whether the key is currently allocated (has been returned from
sys_pkey_alloc() in the past)?

> I.e. something like:
> 
>      unsigned long sys_pkey_alloc (unsigned long flags, unsigned long init_val)
>      unsigned long sys_pkey_set   (int pkey, unsigned long new_val)
>      unsigned long sys_pkey_get   (int pkey)
>      unsigned long sys_pkey_free  (int pkey)
> 
> Optional suggestion:
> 
>  - _Maybe_ also allow the 'remote managed' setup of pkeys: of non-local tasks - 
>    but I'm not sure about that: it looks expensive and complex, and a TID argument 
>    can always be added later if there's some real need.

Yeah, let's see how the stuff above looks first.

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