Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1234367 > unrolled thread

[PATCH 25/25] x86, pkeys: Documentation

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  [PATCH 25/25] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-09-28 21:30 +0200
    Re: [PATCH 25/25] x86, pkeys: Documentation Andi Kleen <andi@firstfloor.org> - 2015-09-28 22:40 +0200
      Re: [PATCH 25/25] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-09-28 22:50 +0200

#1234367 — [PATCH 25/25] x86, pkeys: Documentation

From: Dave Hansen <dave.hansen@linux.intel.com>


Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

 b/Documentation/x86/protection-keys.txt |   54 ++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff -puN /dev/null Documentation/x86/protection-keys.txt
--- /dev/null	2015-07-13 14:24:11.435656502 -0700
+++ b/Documentation/x86/protection-keys.txt	2015-09-28 11:40:16.120555350 -0700
@@ -0,0 +1,54 @@
+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.
+
+The kernel attempts to make protection keys consistent with the
+behavior of a plain mprotect().  For instance if you do this:
+
+	mprotect(ptr, size, PROT_NONE);
+	something(ptr);
+
+you can expect the same effects with protection keys when doing this:
+
+	mprotect(ptr, size, PROT_READ|PROT_WRITE);
+	set_pkey(ptr, size, 4);
+	wrpkru(0xffffff3f); // access disable pkey 4
+	something(ptr);
+
+That should be true whether something() is a direct access to 'ptr'
+like:
+
+	*ptr = foo;
+
+or when the kernel does the access on the application's behalf like
+with a read():
+
+	read(fd, ptr, 1);
+
+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.
+
+=========================== Config Option ===========================
+
+This config option adds approximately 1.5kb of text. and 50 bytes of
+data to the executable.  A workload which does large O_DIRECT reads
+of holes in XFS files was run to exercise get_user_pages_fast().  No
+performance delta was observed with the config option
+enabled or disabled.
_
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1234428

Dave Hansen <dave@sr71.net> writes:

> From: Dave Hansen <dave.hansen@linux.intel.com>

Do you have a manpage for the new syscall too?

-Andi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1234432

[Multipart message — attachments visible in raw view] — view raw

On 09/28/2015 01:34 PM, Andi Kleen wrote:
> Do you have a manpage for the new syscall too?

Yep, I just added it to the mprotect() manpage.

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web