pkeys: Reserve PKEY_DISABLE_READ
Florian Weimer
fweimer at redhat.com
Tue Dec 4 02:52:02 AEDT 2018
* Ram Pai:
> So the problem is as follows:
>
> Currently the kernel supports 'disable-write' and 'disable-access'.
>
> On x86, cpu supports 'disable-write' and 'disable-access'. This
> matches with what the kernel supports. All good.
>
> However on power, cpu supports 'disable-read' too. Since userspace can
> program the cpu directly, userspace has the ability to set
> 'disable-read' too. This can lead to inconsistency between the kernel
> and the userspace.
>
> We want the kernel to match userspace on all architectures.
Correct.
> Proposed Solution:
>
> Enhance the kernel to understand 'disable-read', and facilitate architectures
> that understand 'disable-read' to allow it.
>
> Also explicitly define the semantics of disable-access as
> 'disable-read and disable-write'
>
> Did I get this right? Assuming I did, the implementation has to do
> the following --
>
> On power, sys_pkey_alloc() should succeed if the init_val
> is PKEY_DISABLE_READ, PKEY_DISABLE_WRITE, PKEY_DISABLE_ACCESS
> or any combination of the three.
Agreed.
> On x86, sys_pkey_alloc() should succeed if the init_val is
> PKEY_DISABLE_WRITE or PKEY_DISABLE_ACCESS or PKEY_DISABLE_READ
> or any combination of the three, except PKEY_DISABLE_READ
> specified all by itself.
Again agreed. That's a clever way of phrasing it actually.
> On all other arches, none of the flags are supported.
>
>
> Are we on the same plate?
I think so, thanks.
Florian
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