lkml.org 
[lkml]   [2015]   [Dec]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 26/34] mm: implement new mprotect_key() system call
Hi Dave,

On 9 December 2015 at 16:48, Dave Hansen <dave@sr71.net> wrote:
> Hi Michael,
>
> Thanks for all the comments! I'll fix most of it when I post a new
> version of the manpage, but I have a few general questions.
>
> On 12/09/2015 03:08 AM, Michael Kerrisk (man-pages) wrote:
>>>
>>> +is the protection or storage key to assign to the memory.
>>
>> Why "protection or storage key" here? This phrasing seems a
>> little ambiguous to me, given that we also have a 'prot'
>> argument. I think it would be clearer just to say
>> "protection key". But maybe I'm missing something.
>
> x86 calls it a "protection key" while powerpc calls it a "storage key".
> They're called "protection keys" consistently inside the kernel.
>
> Should we just stick to one name in the manpages?

Yes. But perhaps you could note the alternate name in the pkey(7) page.

>> * A general overview of why this functionality is useful.
>
> Any preference on a central spot to do the general overview? Does it go
> in one of the manpages I'm already modifying, or a new one?

How about we add one more page, pkey(7) that gives the overview and
also summarizes the APIs.

>> * A note on which architectures support/will support
>> this functionality.
>
> x86 only for now. We might get powerpc support down the road somewhere.

Supported architectures can be listed in pkey(7).

>> * Explanation of what a protection domain is.
>
> A protection domain is a unique view of memory and is represented by the
> value in the PKRU register.

Out something about this in pkey(7), but explain what you mean by a
"unique view of memory".

>> * Explanation of how a process (thread?) changes its
>> protection domain.
>
> Changing protection domains is done by pkey_set() system call, or by
> using the WRPKRU instruction. The system call is preferred and less
> error-prone since it enforces that a protection is allocated before its
> access protection can be modified.

Details (perhaps not the WRPKRU bit) that should go in pkey(7).

>> * Explanation of the relationship between page permission
>> bits (PROT_READ/PROT_WRITE/PROTE_EXEC) and
>> PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE.
>> It's still not clear to me. Do the PKEY_* bits
>> override the PROT_* bits. Or, something else?
>
> Protection keys add access restrictions in addition to existing page
> permissions. They can only take away access; they never grant
> additional access.

This belongs in pkey(7) :-).

Cheers,

Michael

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/


\
 
 \ /
  Last update: 2015-12-09 18:01    [W:0.188 / U:0.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site