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From: Dave Hansen <dave@sr71.net>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-mm@kvack.org, torvalds@linux-foundation.org,
	akpm@linux-foundation.org, dave.hansen@linux.intel.com
Subject: Re: [PATCH 2/9] mm: implement new pkey_mprotect() system call
Date: Mon, 13 Jun 2016 09:03:36 -0700	[thread overview]
Message-ID: <575ED958.5060209@sr71.net> (raw)
In-Reply-To: <alpine.DEB.2.11.1606111147000.5839@nanos>

On 06/11/2016 02:47 AM, Thomas Gleixner wrote:
> On Wed, 8 Jun 2016, Dave Hansen wrote:
>> > Proposed semantics:
>> > 1. protection key 0 is special and represents the default,
>> >    unassigned protection key.  It is always allocated.
>> > 2. mprotect() never affects a mapping's pkey_mprotect()-assigned
>> >    protection key. A protection key of 0 (even if set explicitly)
>> >    represents an unassigned protection key.
>> >    2a. mprotect(PROT_EXEC) on a mapping with an assigned protection
>> >        key may or may not result in a mapping with execute-only
>> >        properties.  pkey_mprotect() plus pkey_set() on all threads
>> >        should be used to _guarantee_ execute-only semantics.
>> > 3. mprotect(PROT_EXEC) may result in an "execute-only" mapping. The
>> >    kernel will internally attempt to allocate and dedicate a
>> >    protection key for the purpose of execute-only mappings.  This
>> >    may not be possible in cases where there are no free protection
>> >    keys available.
> Shouldn't we just reserve a protection key for PROT_EXEC unconditionally?

Normal userspace does not do PROT_EXEC today.  So, today, we'd
effectively lose one of our keys by reserving it.  Of the folks I've
talked to who really want this feature, and *will* actually use it, one
of the most common complaints is that there are too few keys.

Folks who actively *want* true PROT_EXEC semantics can use the explicit
pkey interfaces.

  reply	other threads:[~2016-06-13 16:03 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-09  0:01 [PATCH 0/9] [v3] System Calls for Memory Protection Keys Dave Hansen
2016-06-09  0:01 ` [PATCH 1/9] x86, pkeys: add fault handling for PF_PK page fault bit Dave Hansen
2016-06-09  0:01 ` [PATCH 2/9] mm: implement new pkey_mprotect() system call Dave Hansen
2016-06-11  9:47   ` Thomas Gleixner
2016-06-13 16:03     ` Dave Hansen [this message]
2016-06-09  0:01 ` [PATCH 3/9] x86, pkeys: make mprotect_key() mask off additional vm_flags Dave Hansen
2016-06-09  0:01 ` [PATCH 4/9] x86: wire up mprotect_key() system call Dave Hansen
2016-06-09  0:01 ` [PATCH 5/9] x86, pkeys: allocation/free syscalls Dave Hansen
2016-06-09  0:01 ` [PATCH 6/9] x86, pkeys: add pkey set/get syscalls Dave Hansen
2016-06-09  0:01 ` [PATCH 7/9] generic syscalls: wire up memory protection keys syscalls Dave Hansen
2016-06-09  0:01 ` [PATCH 8/9] pkeys: add details of system call use to Documentation/ Dave Hansen
2016-06-09  0:01 ` [PATCH 9/9] x86, pkeys: add self-tests Dave Hansen
2016-06-30  9:41 ` [PATCH 0/9] [v3] System Calls for Memory Protection Keys Ingo Molnar
2016-06-30 16:46   ` Dave Hansen
2016-06-30 17:40     ` Andy Lutomirski
  -- strict thread matches above, loose matches on Subject: below --
2016-07-07 12:47 [PATCH 0/9] [REVIEW-REQUEST] [v4] " Dave Hansen
2016-07-07 12:47 ` [PATCH 2/9] mm: implement new pkey_mprotect() system call Dave Hansen
2016-07-07 14:40   ` Mel Gorman
2016-07-07 16:51     ` Dave Hansen
2016-07-08 10:15       ` Mel Gorman
2016-06-07 20:47 [PATCH 0/9] [v2] System Calls for Memory Protection Keys Dave Hansen
2016-06-07 20:47 ` [PATCH 2/9] mm: implement new pkey_mprotect() system call Dave Hansen

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