From: Ram Pai <linuxram@us.ibm.com>
To: 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
Cc: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com,
bsingharora@gmail.com, dave.hansen@intel.com, hbabu@us.ibm.com,
linuxram@us.ibm.com, arnd@arndb.de, akpm@linux-foundation.org,
corbet@lwn.net, mingo@redhat.com
Subject: [RFC v3 22/23] Documentation: PowerPC specific updates to memory protection keys
Date: Wed, 21 Jun 2017 18:39:38 -0700 [thread overview]
Message-ID: <1498095579-6790-23-git-send-email-linuxram@us.ibm.com> (raw)
In-Reply-To: <1498095579-6790-1-git-send-email-linuxram@us.ibm.com>
Add documentation updates that capture PowerPC specific changes.
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
---
Documentation/vm/protection-keys.txt | 65 +++++++++++++++++++++++++-----------
1 file changed, 45 insertions(+), 20 deletions(-)
diff --git a/Documentation/vm/protection-keys.txt b/Documentation/vm/protection-keys.txt
index b643045..965ad75 100644
--- a/Documentation/vm/protection-keys.txt
+++ b/Documentation/vm/protection-keys.txt
@@ -1,21 +1,46 @@
-Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature
-which will be found on future Intel CPUs.
+Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature found in
+new generation of intel CPUs and on PowerPC 7 and higher CPUs.
Memory Protection Keys provides a mechanism for enforcing page-based
-protections, but without requiring modification of the page tables
-when an application changes protection domains. It works by
-dedicating 4 previously ignored bits in each page table entry to a
-"protection key", giving 16 possible keys.
-
-There is also a new user-accessible register (PKRU) with two separate
-bits (Access Disable and Write Disable) for each key. Being a CPU
-register, PKRU is inherently thread-local, potentially giving each
-thread a different set of protections from every other thread.
-
-There are two new instructions (RDPKRU/WRPKRU) for reading and writing
-to the new register. The feature is only available in 64-bit mode,
-even though there is theoretically space in the PAE PTEs. These
-permissions are enforced on data access only and have no effect on
+protections, but without requiring modification of the page tables when an
+application changes protection domains.
+
+
+On Intel:
+
+ It works by dedicating 4 previously ignored bits in each page table
+ entry to a "protection key", giving 16 possible keys.
+
+ There is also a new user-accessible register (PKRU) with two separate
+ bits (Access Disable and Write Disable) for each key. Being a CPU
+ register, PKRU is inherently thread-local, potentially giving each
+ thread a different set of protections from every other thread.
+
+ There are two new instructions (RDPKRU/WRPKRU) for reading and writing
+ to the new register. The feature is only available in 64-bit mode,
+ even though there is theoretically space in the PAE PTEs. These
+ permissions are enforced on data access only and have no effect on
+ instruction fetches.
+
+
+On PowerPC:
+
+ It works by dedicating 5 page table entry bits to a "protection key",
+ giving 32 possible keys.
+
+ There is a user-accessible register (AMR) with two separate bits;
+ Access Disable and Write Disable, for each key. Being a CPU
+ register, AMR is inherently thread-local, potentially giving each
+ thread a different set of protections from every other thread. NOTE:
+ Disabling read permission does not disable write and vice-versa.
+
+ The feature is available on 64-bit HPTE mode only.
+ 'mtspr 0xd, mem' reads the AMR register
+ 'mfspr mem, 0xd' writes into the AMR register.
+
+
+
+Permissions are enforced on data access only and have no effect on
instruction fetches.
=========================== Syscalls ===========================
@@ -28,9 +53,9 @@ There are 3 system calls which directly interact with pkeys:
unsigned long prot, int pkey);
Before a pkey can be used, it must first be allocated with
-pkey_alloc(). An application calls the WRPKRU instruction
+pkey_alloc(). An application calls the WRPKRU/AMR instruction
directly in order to change access permissions to memory covered
-with a key. In this example WRPKRU is wrapped by a C function
+with a key. In this example WRPKRU/AMR is wrapped by a C function
called pkey_set().
int real_prot = PROT_READ|PROT_WRITE;
@@ -52,11 +77,11 @@ is no longer in use:
munmap(ptr, PAGE_SIZE);
pkey_free(pkey);
-(Note: pkey_set() is a wrapper for the RDPKRU and WRPKRU instructions.
+(Note: pkey_set() is a wrapper for the RDPKRU,WRPKRU or AMR instructions.
An example implementation can be found in
tools/testing/selftests/x86/protection_keys.c)
-=========================== Behavior ===========================
+=========================== Behavior =================================
The kernel attempts to make protection keys consistent with the
behavior of a plain mprotect(). For instance if you do this:
--
1.8.3.1
next prev parent reply other threads:[~2017-06-22 1:40 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-22 1:39 [RFC v3 00/23] powerpc: Memory Protection Keys Ram Pai
2017-06-22 1:39 ` [RFC v3 01/23] powerpc: Free up four 64K PTE bits in 4K backed HPTE pages Ram Pai
2017-06-22 9:21 ` Balbir Singh
2017-06-22 18:50 ` Ram Pai
2017-06-22 1:39 ` [RFC v3 02/23] powerpc: introduce set_hidx_slot helper Ram Pai
2017-06-25 23:03 ` Balbir Singh
2017-06-26 4:02 ` Benjamin Herrenschmidt
2017-06-27 0:17 ` Ram Pai
2017-06-27 0:16 ` Ram Pai
2017-06-22 1:39 ` [RFC v3 03/23] powerpc: introduce get_hidx_gslot helper Ram Pai
2017-06-22 1:39 ` [RFC v3 04/23] powerpc: Free up four 64K PTE bits in 64K backed HPTE pages Ram Pai
2017-06-22 1:39 ` [RFC v3 05/23] powerpc: capture the PTE format changes in the dump pte report Ram Pai
2017-06-22 1:39 ` [RFC v3 06/23] powerpc: use helper functions in __hash_page_4K() for 64K PTE Ram Pai
2017-06-22 1:39 ` [RFC v3 07/23] powerpc: use helper functions in __hash_page_4K() for 4K PTE Ram Pai
2017-06-22 1:39 ` [RFC v3 08/23] powerpc: use helper functions in flush_hash_page() Ram Pai
2017-06-22 1:39 ` [RFC v3 09/23] mm: introduce an additional vma bit for powerpc pkey Ram Pai
2017-06-22 1:39 ` [RFC v3 10/23] mm: provide the ability to disable execute on a key at creation Ram Pai
2017-06-22 1:39 ` [RFC v3 11/23] x86: key creation with PKEY_DISABLE_EXECUTE is disallowed Ram Pai
2017-06-22 1:39 ` [RFC v3 12/23] powerpc: Implement sys_pkey_alloc and sys_pkey_free system call Ram Pai
2017-06-22 1:39 ` [RFC v3 13/23] powerpc: store and restore the pkey state across context switches Ram Pai
2017-06-22 1:39 ` [RFC v3 14/23] powerpc: Implementation for sys_mprotect_pkey() system call Ram Pai
2017-06-22 1:39 ` [RFC v3 15/23] powerpc: Program HPTE key protection bits Ram Pai
2017-06-22 1:39 ` [RFC v3 16/23] powerpc: Macro the mask used for checking DSI exception Ram Pai
2017-06-22 1:39 ` [RFC v3 17/23] powerpc: Handle exceptions caused by violation of pkey protection Ram Pai
2017-06-22 1:39 ` [RFC v3 18/23] powerpc: Deliver SEGV signal on pkey violation Ram Pai
2017-06-22 1:39 ` [RFC v3 19/23] selftest: Move protecton key selftest to arch neutral directory Ram Pai
2017-06-22 1:39 ` [RFC v3 20/23] selftest: PowerPC specific test updates to memory protection keys Ram Pai
2017-06-22 1:39 ` [RFC v3 21/23] Documentation: Move protecton key documentation to arch neutral directory Ram Pai
2017-06-22 1:39 ` Ram Pai [this message]
2017-06-22 1:39 ` [RFC v3 23/23] procfs: display the protection-key number associated with a vma Ram Pai
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