From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-x242.google.com (mail-qt0-x242.google.com [IPv6:2607:f8b0:400d:c0d::242]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4099Qt0rPTzF21y for ; Tue, 27 Mar 2018 10:32:05 +1100 (AEDT) Received: by mail-qt0-x242.google.com with SMTP id l18so5140262qtj.1 for ; Mon, 26 Mar 2018 16:32:05 -0700 (PDT) Sender: Ram Pai From: Ram Pai To: mpe@ellerman.id.au, mingo@redhat.com, akpm@linux-foundation.org Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, dave.hansen@intel.com, benh@kernel.crashing.org, paulus@samba.org, aneesh.kumar@linux.vnet.ibm.com, bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org, bauerman@linux.vnet.ibm.com, linuxram@us.ibm.com, fweimer@redhat.com, msuchanek@suse.com, tglx@linutronix.de, shuah@kernel.org Subject: [PATCH] powerpc, pkey: make protection key 0 less special Date: Mon, 26 Mar 2018 16:31:41 -0700 Message-Id: <1522107101-16083-1-git-send-email-linuxram@us.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Applications need the ability to associate an address-range with some key and latter revert to its initial default key. Pkey-0 comes close to providing this function but falls short, because the current implementation disallows applications to explicitly associate pkey-0 to the address range. Lets make pkey-0 less special and treat it almost like any other key. Thus it can be explicitly associated with any address range, and can be freed. This gives the application more flexibility and power. The ability to free pkey-0 must be used responsibily, since pkey-0 is associated with almost all address-range by default. Even with this change pkey-0 continues to be slightly more special from the following point of view. (a) it is implicitly allocated. (b) it is the default key assigned to any address-range. Tested on powerpc. cc: Thomas Gleixner cc: Dave Hansen cc: Michael Ellermen cc: Ingo Molnar cc: Andrew Morton Signed-off-by: Ram Pai --- arch/powerpc/include/asm/pkeys.h | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h index 0409c80..9c7d3bd 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; + + return __mm_pkey_is_allocated(mm, pkey); } extern void __arch_activate_pkey(int pkey); @@ -200,6 +208,14 @@ static inline int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, { if (static_branch_likely(&pkey_disabled)) return -EINVAL; + + /* + * userspace is discouraged from changing permissions of + * pkey-0. powerpc hardware does not support it anyway. + */ + if (!pkey) + return init_val ? -EINVAL : 0; + return __arch_set_user_pkey_access(tsk, pkey, init_val); } -- 1.8.3.1