linux-kernel - Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0

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Date:   Fri, 9 Mar 2018 12:09:17 -0800
From:   Ram Pai <linuxram@...ibm.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     mpe@...erman.id.au, mingo@...hat.com, akpm@...ux-foundation.org,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org, x86@...nel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, mhocko@...nel.org,
        bauerman@...ux.vnet.ibm.com, ebiederm@...ssion.com, corbet@....net,
        arnd@...db.de, fweimer@...hat.com, msuchanek@...e.com,
        Ulrich.Weigand@...ibm.com
Subject: Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0

On Fri, Mar 09, 2018 at 09:43:32AM +0100, Ingo Molnar wrote:
> 
> * Ram Pai <linuxram@...ibm.com> wrote:
> 
> > Once an address range is associated with an allocated pkey, it cannot be
> > reverted back to key-0. There is no valid reason for the above behavior.  On
> > the contrary applications need the ability to do so.
> > 
> > The patch relaxes the restriction.
> > 
> > Tested on powerpc and x86_64.
> > 
> > cc: Dave Hansen <dave.hansen@...el.com>
> > cc: Michael Ellermen <mpe@...erman.id.au>
> > cc: Ingo Molnar <mingo@...nel.org>
> > Signed-off-by: Ram Pai <linuxram@...ibm.com>
> > ---
> >  arch/powerpc/include/asm/pkeys.h | 19 ++++++++++++++-----
> >  arch/x86/include/asm/pkeys.h     |  5 +++--
> >  2 files changed, 17 insertions(+), 7 deletions(-)
> > 
> > diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
> > index 0409c80..3e8abe4 100644
> > --- a/arch/powerpc/include/asm/pkeys.h
> > +++ b/arch/powerpc/include/asm/pkeys.h
> > @@ -101,10 +101,18 @@ static inline u16 pte_to_pkey_bits(u64 pteflags)
> >  
> >  static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
> >  {
> > -	/* A reserved key is never considered as 'explicitly allocated' */
> > -	return ((pkey < arch_max_pkey()) &&
> > -		!__mm_pkey_is_reserved(pkey) &&
> > -		__mm_pkey_is_allocated(mm, pkey));
> > +	/* pkey 0 is allocated by default. */
> > +	if (!pkey)
> > +	       return true;
> > +
> > +	if (pkey < 0 || pkey >= arch_max_pkey())
> > +	       return false;
> > +
> > +	/* reserved keys are never allocated. */
> > +	if (__mm_pkey_is_reserved(pkey))
> > +	       return false;
> 
> Please capitalize in comments consistently, i.e.:

ok.

> 
> 	/* Reserved keys are never allocated: */
> 
> > +
> > +	return(__mm_pkey_is_allocated(mm, pkey));
> 
> 'return' is not a function.

right. will fix.

Thanks,
RP