linux-kernel - Re: [PATCH 07/12] mm: Pass the 4-bit protection key in via PROT

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Date:	Thu, 07 May 2015 12:19:23 -0700
From:	Dave Hansen <dave@...1.net>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 07/12] mm: Pass the 4-bit protection key in via PROT_
 bits to syscalls

On 05/07/2015 12:11 PM, One Thousand Gnomes wrote:
>> diff -puN include/uapi/asm-generic/mman-common.h~pkeys-11-user-abi-bits include/uapi/asm-generic/mman-common.h
>> --- a/include/uapi/asm-generic/mman-common.h~pkeys-11-user-abi-bits	2015-05-07 10:31:43.367276719 -0700
>> +++ b/include/uapi/asm-generic/mman-common.h	2015-05-07 10:31:43.370276855 -0700
>> @@ -10,6 +10,10 @@
>>  #define PROT_WRITE	0x2		/* page can be written */
>>  #define PROT_EXEC	0x4		/* page can be executed */
>>  #define PROT_SEM	0x8		/* page may be used for atomic ops */
>> +#define PROT_PKEY0	0x10		/* protection key value (bit 0) */
>> +#define PROT_PKEY1	0x20		/* protection key value (bit 1) */
>> +#define PROT_PKEY2	0x40		/* protection key value (bit 2) */
>> +#define PROT_PKEY3	0x80		/* protection key value (bit 3) */
> 
> Thats leaking deep Intelisms into asm-generic which makes me very
> uncomfortable. Whether we need to reserve some bits for "arch specific"
> is one question, what we do with them ought not to be leaking out.
> 
> To start with trying to port code people will want to do
> 
> #define PROT_PKEY0	0
> #define PROT_PKEY1	0

Yeah, I feel pretty uncomfortable with it as well.  I really don't
expect these to live like this in asm-generic when I submit this.

Powerpc and ia64 have _something_ resembling protection keys, so the
concept isn't entirely x86 or Intel-specific.  My hope would be that we
do this in a way that other architectures can use.


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