From: Ram Pai <linuxram@us.ibm.com>
To: mpe@ellerman.id.au, mingo@redhat.com, akpm@linux-foundation.org,
corbet@lwn.net, arnd@arndb.de
Cc: linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org,
x86@kernel.org, linux-arch@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org, dave.hansen@intel.com,
benh@kernel.crashing.org, paulus@samba.org,
khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com,
bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org,
bauerman@linux.vnet.ibm.com, ebiederm@xmission.com,
linuxram@us.ibm.com
Subject: [PATCH v9 31/51] Documentation/vm: PowerPC specific updates to memory protection keys
Date: Mon, 6 Nov 2017 00:57:23 -0800 [thread overview]
Message-ID: <1509958663-18737-32-git-send-email-linuxram@us.ibm.com> (raw)
In-Reply-To: <1509958663-18737-1-git-send-email-linuxram@us.ibm.com>
Add documentation updates that capture PowerPC specific changes.
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
---
Documentation/vm/protection-keys.txt | 126 +++++++++++++++++++++++++++-------
1 files changed, 101 insertions(+), 25 deletions(-)
diff --git a/Documentation/vm/protection-keys.txt b/Documentation/vm/protection-keys.txt
index fa46dcb..bc079b3 100644
--- a/Documentation/vm/protection-keys.txt
+++ b/Documentation/vm/protection-keys.txt
@@ -1,22 +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 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
-instruction fetches.
+Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature found on
+future Intel CPUs and on PowerPC 5 and higher CPUs.
+
+Memory Protection Keys provide 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 bits in each page table entry to a "protection key".
+There is also a user-accessible register with two separate bits for each
+key. Being a CPU register, the user-accessible register is inherently
+thread-local, potentially giving each thread a different set of protections
+from every other thread.
+
+On Intel:
+
+ Four previously bits are used the page table entry giving 16 possible keys.
+
+ The user accessible register(PKRU) has a bit each per key to disable
+ access and to disable write.
+
+ 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:
+
+ Five bits in the page table entry are used giving 32 possible keys.
+ This support is currently for Hash Page Table mode only.
+
+ The user accessible register(AMR) has a bit each per key to disable
+ read and write. Access disable can be achieved by disabling
+ read and write.
+
+ 'mtspr 0xd, mem' reads the AMR register
+ 'mfspr mem, 0xd' writes into the AMR register.
+
+ Execution can be disabled by allocating a key with execute-disabled
+ permission. The execute-permissions on the key; however, cannot be
+ changed through a user accessible register. Instead; a powerpc specific
+ system call sys_pkey_modify() must be used. The CPU will not allow
+ execution of instruction in pages that are associated with
+ execute-disabled key.
+
=========================== Syscalls ===========================
@@ -28,9 +52,9 @@ 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 +76,11 @@ 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)
+ tools/testing/selftests/vm/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:
@@ -66,7 +90,7 @@ behavior of a plain mprotect(). For instance if you do this:
you can expect the same effects with protection keys when doing this:
- pkey = pkey_alloc(0, PKEY_DISABLE_WRITE | PKEY_DISABLE_READ);
+ pkey = pkey_alloc(0, PKEY_DISABLE_ACCESS);
pkey_mprotect(ptr, size, PROT_READ|PROT_WRITE, pkey);
something(ptr);
@@ -83,3 +107,55 @@ with a read():
The kernel will send a SIGSEGV in both cases, but si_code will be set
to SEGV_PKERR when violating protection keys versus SEGV_ACCERR when
the plain mprotect() permissions are violated.
+
+========================== sysfs Interface ==========================
+
+Information about support of protection keys on the system can be
+found in the /sys/kernel/mm/protection_keys directory, which
+contains the following files:
+
+- total_keys: Shows the number of keys supported by the hardware.
+ Not all of those keys may be available for use by a process
+ because the platform or operating system may reserve some keys
+ for their own use.
+
+- usable_keys: Shows the minimum number of keys guaranteed to be
+ available for use by a process. In other words: total_keys minus
+ the keys reserved by the platform or operating system. This
+ number doesn't change to reflect keys that are already being
+ used by the process reading the file.
+
+ There may be one more key available than what is advertised in
+ this file because the kernel may use one key for mprotect()
+ calls setting up memory with execute-only permissions. This file
+ assumes that this key is being used, but if it is not the
+ process will have one more key it can use for other purposes.
+
+- disable_access_supported: Shows 'true' if the system supports keys
+ which disallow reading from a given page (i.e., the
+ PKEY_DISABLE_ACCESS flag is supported).
+
+- disable_write_supported: Shows 'true' if the system supports keys
+ which disallow writing to a given page (i.e., the
+ PKEY_DISABLE_WRITE flag is supported).
+
+- disable_execute_supported: Shows 'true' if the system supports keys
+ which disallow code execution from a given page (i.e., the
+ PKEY_DISABLE_EXECUTE flag is supported).
+
+====================================================================
+ Differences
+
+The following differences exist between x86 and power.
+
+a) powerpc (PowerPC8 onwards) *also* allows creation of a key with
+ execute-disabled.
+ The following is allowed
+ pkey = pkey_alloc(0, PKEY_DISABLE_EXECUTE);
+
+b) On powerpc the access/write permission on a key can be modified by
+ programming the AMR register from the signal handler. The changes
+ persist across signal boundaries. On x86, the PKRU specific fpregs
+ entry has to be modified to change the access/write permission on
+ a key.
+=====================================================================
--
1.7.1
next prev parent reply other threads:[~2017-11-06 8:59 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-06 8:56 [PATCH v9 00/51] powerpc, mm: Memory Protection Keys Ram Pai
2017-11-06 8:56 ` [PATCH v9 01/51] mm, powerpc, x86: define VM_PKEY_BITx bits if CONFIG_ARCH_HAS_PKEYS is enabled Ram Pai
2017-11-06 8:56 ` [PATCH v9 02/51] mm, powerpc, x86: introduce an additional vma bit for powerpc pkey Ram Pai
2017-11-06 8:56 ` [PATCH v9 03/51] powerpc: initial pkey plumbing Ram Pai
2017-11-06 8:56 ` [PATCH v9 04/51] powerpc: track allocation status of all pkeys Ram Pai
2017-11-06 8:56 ` [PATCH v9 05/51] powerpc: helper function to read, write AMR, IAMR, UAMOR registers Ram Pai
2017-11-06 8:56 ` [PATCH v9 06/51] powerpc: helper functions to initialize AMR, IAMR and " Ram Pai
2017-11-06 8:56 ` [PATCH v9 07/51] powerpc: cleanup AMR, IAMR when a key is allocated or freed Ram Pai
2017-11-06 8:57 ` [PATCH v9 08/51] powerpc: implementation for arch_set_user_pkey_access() Ram Pai
2017-11-06 8:57 ` [PATCH v9 09/51] powerpc: ability to create execute-disabled pkeys Ram Pai
2017-11-06 8:57 ` [PATCH v9 10/51] powerpc: store and restore the pkey state across context switches Ram Pai
2017-11-06 8:57 ` [PATCH v9 11/51] powerpc: introduce execute-only pkey Ram Pai
2017-11-06 8:57 ` [PATCH v9 12/51] powerpc: ability to associate pkey to a vma Ram Pai
2017-11-06 8:57 ` [PATCH v9 13/51] powerpc: implementation for arch_override_mprotect_pkey() Ram Pai
2017-11-06 8:57 ` [PATCH v9 14/51] powerpc: map vma key-protection bits to pte key bits Ram Pai
2017-11-06 8:57 ` [PATCH v9 15/51] powerpc: Program HPTE key protection bits Ram Pai
2017-11-06 8:57 ` [PATCH v9 16/51] powerpc: helper to validate key-access permissions of a pte Ram Pai
2017-11-06 8:57 ` [PATCH v9 17/51] powerpc: check key protection for user page access Ram Pai
2017-11-06 8:57 ` [PATCH v9 18/51] powerpc: implementation for arch_vma_access_permitted() Ram Pai
2017-11-06 8:57 ` [PATCH v9 19/51] powerpc: Handle exceptions caused by pkey violation Ram Pai
2017-11-06 8:57 ` [PATCH v9 20/51] powerpc: introduce get_mm_addr_key() helper Ram Pai
2017-11-06 8:57 ` [PATCH v9 21/51] powerpc: Deliver SEGV signal on pkey violation Ram Pai
2017-11-06 8:57 ` [PATCH v9 22/51] powerpc/ptrace: Add memory protection key regset Ram Pai
2017-11-06 8:57 ` [PATCH v9 23/51] powerpc: Enable pkey subsystem Ram Pai
2017-11-13 0:54 ` Ram Pai
2017-11-06 8:57 ` [PATCH v9 24/51] powerpc: sys_pkey_alloc() and sys_pkey_free() system calls Ram Pai
2017-11-06 8:57 ` [PATCH v9 25/51] powerpc: sys_pkey_mprotect() system call Ram Pai
2017-11-06 8:57 ` [PATCH v9 26/51] powerpc: add sys_pkey_modify() " Ram Pai
2017-11-06 8:57 ` [PATCH v9 27/51] mm, x86 : introduce arch_pkeys_enabled() Ram Pai
2017-11-06 8:57 ` [PATCH v9 28/51] mm: display pkey in smaps if arch_pkeys_enabled() is true Ram Pai
2017-11-06 8:57 ` [PATCH v9 29/51] mm/mprotect, powerpc/mm/pkeys, x86/mm/pkeys: Add sysfs interface Ram Pai
2017-12-18 18:54 ` Dave Hansen
2017-12-18 22:18 ` Ram Pai
2017-12-18 22:28 ` Dave Hansen
2017-12-18 23:15 ` Ram Pai
2017-12-19 8:31 ` Gabriel Paubert
2017-12-19 16:22 ` Ram Pai
2017-12-19 21:34 ` Benjamin Herrenschmidt
2017-12-20 17:50 ` Ram Pai
2017-12-20 22:49 ` Benjamin Herrenschmidt
2017-12-19 10:50 ` Michael Ellerman
2017-12-19 16:32 ` Ram Pai
2017-11-06 8:57 ` [PATCH v9 30/51] Documentation/x86: Move protecton key documentation to arch neutral directory Ram Pai
2017-11-06 8:57 ` Ram Pai [this message]
2017-11-06 8:57 ` [PATCH v9 32/51] selftest/x86: Move protecton key selftest " Ram Pai
2017-11-06 8:57 ` [PATCH v9 33/51] selftest/vm: rename all references to pkru to a generic name Ram Pai
2017-11-06 8:57 ` [PATCH v9 34/51] selftest/vm: move generic definitions to header file Ram Pai
2017-11-06 8:57 ` [PATCH v9 35/51] selftest/vm: typecast the pkey register Ram Pai
2017-11-06 8:57 ` [PATCH v9 36/51] selftest/vm: generic function to handle shadow key register Ram Pai
2017-11-06 8:57 ` [PATCH v9 37/51] selftest/vm: fix the wrong assert in pkey_disable_set() Ram Pai
2017-11-06 8:57 ` [PATCH v9 38/51] selftest/vm: fixed bugs in pkey_disable_clear() Ram Pai
2017-11-06 8:57 ` [PATCH v9 39/51] selftest/vm: clear the bits in shadow reg when a pkey is freed Ram Pai
2017-11-06 8:57 ` [PATCH v9 40/51] selftest/vm: fix alloc_random_pkey() to make it really random Ram Pai
2017-11-06 8:57 ` [PATCH v9 41/51] selftest/vm: introduce two arch independent abstraction Ram Pai
2017-11-06 8:57 ` [PATCH v9 42/51] selftest/vm: pkey register should match shadow pkey Ram Pai
2017-11-06 8:57 ` [PATCH v9 43/51] selftest/vm: generic cleanup Ram Pai
2017-11-06 8:57 ` [PATCH v9 44/51] selftest/vm: powerpc implementation for generic abstraction Ram Pai
2017-11-09 18:47 ` Breno Leitao
2017-11-09 23:37 ` Ram Pai
2017-11-10 11:36 ` Breno Leitao
2017-11-06 8:57 ` [PATCH v9 45/51] selftest/vm: fix an assertion in test_pkey_alloc_exhaust() Ram Pai
2017-11-06 8:57 ` [PATCH v9 46/51] selftest/vm: associate key on a mapped page and detect access violation Ram Pai
2017-11-06 8:57 ` [PATCH v9 47/51] selftest/vm: associate key on a mapped page and detect write violation Ram Pai
2017-11-06 8:57 ` [PATCH v9 48/51] selftest/vm: detect write violation on a mapped access-denied-key page Ram Pai
2017-11-06 8:57 ` [PATCH v9 49/51] selftest/vm: sub-page allocator Ram Pai
2017-11-06 8:57 ` [PATCH v9 50/51] selftests/powerpc: Add ptrace tests for Protection Key register Ram Pai
2017-11-06 8:57 ` [PATCH v9 51/51] selftests/powerpc: Add core file test " Ram Pai
2017-11-06 21:28 ` [PATCH v9 00/51] powerpc, mm: Memory Protection Keys Florian Weimer
2017-11-07 1:22 ` Ram Pai
2017-11-07 7:32 ` Florian Weimer
2017-11-07 22:39 ` Ram Pai
2017-11-07 22:47 ` Dave Hansen
2017-11-07 23:44 ` Ram Pai
2017-11-09 22:23 ` Ram Pai
2017-11-10 18:10 ` Christophe LEROY
2017-11-12 20:45 ` Ram Pai
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1509958663-18737-32-git-send-email-linuxram@us.ibm.com \
--to=linuxram@us.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=aneesh.kumar@linux.vnet.ibm.com \
--cc=arnd@arndb.de \
--cc=bauerman@linux.vnet.ibm.com \
--cc=benh@kernel.crashing.org \
--cc=bsingharora@gmail.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@intel.com \
--cc=ebiederm@xmission.com \
--cc=hbabu@us.ibm.com \
--cc=khandual@linux.vnet.ibm.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mhocko@kernel.org \
--cc=mingo@redhat.com \
--cc=mpe@ellerman.id.au \
--cc=paulus@samba.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).