Date: Sat, 29 Jul 2017 17:39:24 -0700
From: Ram Pai <linuxram@us.ibm.com>
To: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
        linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
        arnd@arndb.de, corbet@lwn.net, mhocko@kernel.org,
        dave.hansen@intel.com, mingo@redhat.com, paulus@samba.org,
        aneesh.kumar@linux.vnet.ibm.com, akpm@linux-foundation.org,
        khandual@linux.vnet.ibm.com
Subject: Re: [RFC v6 27/62] powerpc: helper to validate key-access
 permissions of a pte
Reply-To: Ram Pai <linuxram@us.ibm.com>
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On Fri, Jul 28, 2017 at 06:00:02PM -0300, Thiago Jung Bauermann wrote:
> 
> Ram Pai <linuxram@us.ibm.com> writes:
> > --- a/arch/powerpc/mm/pkeys.c
> > +++ b/arch/powerpc/mm/pkeys.c
> > @@ -201,3 +201,36 @@ int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
> >  	 */
> >  	return vma_pkey(vma);
> >  }
> > +
> > +static bool pkey_access_permitted(int pkey, bool write, bool execute)
> > +{
> > +	int pkey_shift;
> > +	u64 amr;
> > +
> > +	if (!pkey)
> > +		return true;
> > +
> > +	pkey_shift = pkeyshift(pkey);
> > +	if (!(read_uamor() & (0x3UL << pkey_shift)))
> > +		return true;
> > +
> > +	if (execute && !(read_iamr() & (IAMR_EX_BIT << pkey_shift)))
> > +		return true;
> > +
> > +	if (!write) {
> > +		amr = read_amr();
> > +		if (!(amr & (AMR_RD_BIT << pkey_shift)))
> > +			return true;
> > +	}
> > +
> > +	amr = read_amr(); /* delay reading amr uptil absolutely needed */
> 
> Actually, this is causing amr to be read twice in case control enters
> the "if (!write)" block above but doesn't enter the other if block nested
> in it.
> 
> read_amr should be called only once, right before "if (!write)".

the code can be simplified without having to read amr twice.
will fix it.

thanks,
RP

> 
> -- 
> Thiago Jung Bauermann
> IBM Linux Technology Center

-- 
Ram Pai