Subject: Re: [PATCH 11/25] powerpc: introduce execute-only pkey

From: Balbir Singh <[email-masked]>
Date: Thu, 19 Oct 2017 10:02:13 +1100

On Wed, 18 Oct 2017 13:57:39 -0700
Ram Pai <[email-masked]> wrote:

> On Wed, Oct 18, 2017 at 03:15:22PM +1100, Balbir Singh wrote:
> > On Fri,  8 Sep 2017 15:44:59 -0700
> > Ram Pai <[email-masked]> wrote:
> >   
> > > This patch provides the implementation of execute-only pkey.
> > > The architecture-independent layer expects the arch-dependent
> > > layer, to support the ability to create and enable a special
> > > key which has execute-only permission.
> > > 
> > > Signed-off-by: Ram Pai <[email-masked]>
> > > ---
> > >  arch/powerpc/include/asm/book3s/64/mmu.h |    1 +
> > >  arch/powerpc/include/asm/pkeys.h         |    9 ++++-
> > >  arch/powerpc/mm/pkeys.c                  |   57 ++++++++++++++++++++++++++++++
> > >  3 files changed, 66 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
> > > index 55950f4..ee18ba0 100644
> > > --- a/arch/powerpc/include/asm/book3s/64/mmu.h
> > > +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
> > > @@ -115,6 +115,7 @@ struct patb_entry {
> > >  	 * bit unset -> key available for allocation
> > >  	 */
> > >  	u32 pkey_allocation_map;
> > > +	s16 execute_only_pkey; /* key holding execute-only protection */
> > >  #endif
> > >  } mm_context_t;
> > >  
> > > diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
> > > index 78c5362..0cf115f 100644
> > > --- a/arch/powerpc/include/asm/pkeys.h
> > > +++ b/arch/powerpc/include/asm/pkeys.h
> > > @@ -115,11 +115,16 @@ static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
> > >   * Try to dedicate one of the protection keys to be used as an
> > >   * execute-only protection key.
> > >   */
> > > +extern int __execute_only_pkey(struct mm_struct *mm);
> > >  static inline int execute_only_pkey(struct mm_struct *mm)
> > >  {
> > > -	return 0;
> > > +	if (!pkey_inited || !pkey_execute_disable_support)
> > > +		return -1;
> > > +
> > > +	return __execute_only_pkey(mm);
> > >  }
> > >  
> > > +
> > >  static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
> > >  		int prot, int pkey)
> > >  {
> > > @@ -141,6 +146,8 @@ static inline void pkey_mm_init(struct mm_struct *mm)
> > >  	if (!pkey_inited)
> > >  		return;
> > >  	mm_pkey_allocation_map(mm) = initial_allocation_mask;
> > > +	/* -1 means unallocated or invalid */
> > > +	mm->context.execute_only_pkey = -1;
> > >  }
> > >  
> > >  extern void thread_pkey_regs_save(struct thread_struct *thread);
> > > diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> > > index 7cd1be4..8a24983 100644
> > > --- a/arch/powerpc/mm/pkeys.c
> > > +++ b/arch/powerpc/mm/pkeys.c
> > > @@ -188,3 +188,60 @@ void thread_pkey_regs_init(struct thread_struct *thread)
> > >  	write_iamr(0x0ul);
> > >  	write_uamor(0x0ul);
> > >  }
> > > +
> > > +static inline bool pkey_allows_readwrite(int pkey)
> > > +{
> > > +	int pkey_shift = pkeyshift(pkey);
> > > +
> > > +	if (!(read_uamor() & (0x3UL << pkey_shift)))
> > > +		return true;  
> > 
> > If uamor for key 0 is 0x10 for example or 0x01 it's a bug.
> > The above check might miss it.  
> 
> 
> The specs says both the bits corresponding to a key are set or
> reset, cannot be anything else.
>

I agree, thats why I said it's a bug if the values are such.
Do we care to validate that both bits are the same?

Balbir Singh.