[PATCH v2 4/6] powerpc/pkeys: Preallocate execute-only key

[Ram Pai]

On Tue, Jun 19, 2018 at 10:40:13PM +1000, Michael Ellerman wrote:
> Ram Pai <linuxram at us.ibm.com> writes:
> 
> > execute-only key is allocated dynamically. This is a problem.  When a
> > thread implicitly creates a execute-only key, and resets UAMOR for that
> > key, the UAMOR value does not percolate to all the other threads.  Any
> > other thread may ignorantly change the permissions on the key.  This can
> > cause the key to be not execute-only for that thread.
> >
> > Preallocate the execute-only key and ensure that no thread can change
> > the permission of the key, by resetting the corresponding bit in UAMOR.
> 
> OK this is a non-ABI changing bug fix AFAICS.
> 
> I'll add:
> 
>   Fixes: 5586cf61e108 ("powerpc: introduce execute-only pkey")
>   Cc: stable at vger.kernel.org # v4.16+
> 
> > diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> > index b681bec..1f2389f 100644
> > --- a/arch/powerpc/mm/pkeys.c
> > +++ b/arch/powerpc/mm/pkeys.c
> > @@ -25,6 +25,7 @@
> >  #define IAMR_EX_BIT 0x1UL
> >  #define PKEY_REG_BITS (sizeof(u64)*8)
> >  #define pkeyshift(pkey) (PKEY_REG_BITS - ((pkey+1) * AMR_BITS_PER_PKEY))
> > +#define EXECUTE_ONLY_KEY 2
> 
> Do we ensure we have at least 3 keys anywhere?

No. Good to add. Can this be different patch?

However we do not have any systems with less than 16keys AFAICT.

RP