* Ram Pai:
On Thu, Nov 08, 2018 at 01:05:09PM +0100, Florian Weimer wrote:
quoted
Would it be possible to reserve a bit for PKEY_DISABLE_READ?
I think the POWER implementation can disable read access at the hardware
level, but not write access, and that cannot be expressed with the
current PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE bits.
POWER hardware can disable-read and can **also disable-write**
at the hardware level. It can disable-execute aswell at the
hardware level. For example if the key bits for a given key in the AMR
register is
0b01 it is read-disable
0b10 it is write-disable
To support access-disable, we make the key value 0b11.
So in case if you want to know if the key is read-disable 'bitwise-and' it
against 0x1. i.e (x & 0x1)
Not sure if we covered that alreay, but my problem is that I cannot
translate a 0b01 mask to a PKEY_DISABLE_* flag combination with the
current flags. 0b10 and 0b11 are fine.
POWER also loses the distinction between PKEY_DISABLE_ACCESS and
PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE, but that's fine. This breaks
the current glibc test case, but I have a patch for that. Arguably, the
test is wrong or at least overly strict in what it accepts.
Thanks,
Florian