From: Andy Lutomirski <luto@amacapital.net>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Al Viro <viro@zeniv.linux.org.uk>, X86 ML <x86@kernel.org>,
Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux API <linux-api@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-arch <linux-arch@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Arnd Bergmann <arnd@arndb.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 6/9] x86, pkeys: add pkey set/get syscalls
Date: Tue, 12 Jul 2016 09:32:11 -0700 [thread overview]
Message-ID: <CALCETrUZeZ00sFrTEqWSB-OxkCzGQxknmPTvFe4bv5mKc3hE+Q@mail.gmail.com> (raw)
In-Reply-To: <5783BFB0.70203@intel.com>
On Jul 11, 2016 8:48 AM, "Dave Hansen" <dave.hansen@intel.com> wrote:
>
> On 07/11/2016 07:45 AM, Andy Lutomirski wrote:
> > On Mon, Jul 11, 2016 at 7:34 AM, Dave Hansen <dave@sr71.net> wrote:
> >> Should we instead just recommend to userspace that they lock down access
> >> to keys by default in all threads as a best practice?
> >
> > Is that really better than doing it in-kernel? My concern is that
> > we'll find library code that creates a thread, and that code could run
> > before the pkey-aware part of the program even starts running.
>
> Yeah, so let's assume we have some pkey-unaware thread. The upside of a
> scheme where the kernel preemptively (and transparently to the thread)
> locks down PKRU is that the thread can't go corrupting any non-zero-pkey
> structures that came from other threads.
>
> But, the downside is that the thread can not access any non-zero-pkey
> structures without taking some kind of action with PKRU. That obviously
> won't happen since the thread is pkeys-unaware to begin with. Would
> that break these libraries unless everything using pkeys knows to only
> share pkey=0 data with those threads?
>
Yes, but at least for the cases I can think of, that's probably a good
thing. OTOH, I can see cases where you want everyone to be able to
read but only specific code paths to be able to write.
I think it's more or less impossible to get sensible behavior passing
pkey != 0 data to legacy functions. If you call:
void frob(struct foo *p);
If frob in turn passes p to a thread, what PKRU is it supposed to use?
> > So how is user code supposed lock down all of its threads?
> >
> > seccomp has TSYNC for this, but I don't think that PKRU allows
> > something like that.
>
> I'm not sure this is possible for PKRU. Think of a simple PKRU
> manipulation in userspace:
>
> pkru = rdpkru();
> pkru |= PKEY_DENY_ACCESS<<key*2;
> wrpkru(pkru);
>
> If we push a PKRU value into a thread between the rdpkru() and wrpkru(),
> we'll lose the content of that "push". I'm not sure there's any way to
> guarantee this with a user-controlled register.
We could try to insist that user code uses some vsyscall helper that
tracks which bits are as-yet-unassigned. That's quite messy, though.
We could also arbitrarily partition the key space into
initially-wide-open, initially-read-only, and initially-no-access and
let pkey_alloc say which kind it wants.
--Andy
next prev parent reply other threads:[~2016-07-12 16:32 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-07 12:47 [PATCH 0/9] [REVIEW-REQUEST] [v4] System Calls for Memory Protection Keys Dave Hansen
2016-07-07 12:47 ` [PATCH 1/9] x86, pkeys: add fault handling for PF_PK page fault bit Dave Hansen
2016-07-07 14:40 ` Mel Gorman
2016-07-07 15:42 ` 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
2016-07-07 12:47 ` [PATCH 3/9] x86, pkeys: make mprotect_key() mask off additional vm_flags Dave Hansen
2016-07-07 12:47 ` [PATCH 4/9] x86: wire up mprotect_key() system call Dave Hansen
2016-07-07 12:47 ` [PATCH 5/9] x86, pkeys: allocation/free syscalls Dave Hansen
2016-07-07 14:40 ` Mel Gorman
2016-07-07 15:38 ` Dave Hansen
2016-07-07 12:47 ` [PATCH 6/9] x86, pkeys: add pkey set/get syscalls Dave Hansen
2016-07-07 14:45 ` Mel Gorman
2016-07-07 17:33 ` Dave Hansen
2016-07-08 7:18 ` Ingo Molnar
2016-07-08 16:32 ` Dave Hansen
2016-07-09 8:37 ` Ingo Molnar
2016-07-11 4:25 ` Andy Lutomirski
2016-07-11 7:35 ` Ingo Molnar
2016-07-11 14:28 ` Dave Hansen
2016-07-12 7:13 ` Ingo Molnar
2016-07-12 15:39 ` Dave Hansen
2016-07-11 14:50 ` Andy Lutomirski
2016-07-11 14:34 ` Dave Hansen
2016-07-11 14:45 ` Andy Lutomirski
2016-07-11 15:48 ` Dave Hansen
2016-07-12 16:32 ` Andy Lutomirski [this message]
2016-07-12 17:12 ` Dave Hansen
2016-07-12 22:55 ` Andy Lutomirski
2016-07-13 7:56 ` Ingo Molnar
2016-07-13 18:43 ` Andy Lutomirski
2016-07-14 8:07 ` Ingo Molnar
2016-07-18 4:43 ` Andy Lutomirski
2016-07-18 9:56 ` Ingo Molnar
2016-07-18 18:02 ` Dave Hansen
2016-07-18 20:12 ` Dave Hansen
2016-07-08 19:26 ` Dave Hansen
2016-07-08 10:22 ` Mel Gorman
2016-07-07 12:47 ` [PATCH 7/9] generic syscalls: wire up memory protection keys syscalls Dave Hansen
2016-07-07 12:47 ` [PATCH 8/9] pkeys: add details of system call use to Documentation/ Dave Hansen
2016-07-07 12:47 ` [PATCH 9/9] x86, pkeys: add self-tests Dave Hansen
2016-07-07 14:47 ` [PATCH 0/9] [REVIEW-REQUEST] [v4] System Calls for Memory Protection Keys Mel Gorman
2016-07-08 18:38 ` Hugh Dickins
-- strict thread matches above, loose matches on Subject: below --
2016-06-09 0:01 [PATCH 0/9] [v3] " Dave Hansen
2016-06-09 0:01 ` [PATCH 6/9] x86, pkeys: add pkey set/get syscalls Dave Hansen
2016-06-07 20:47 [PATCH 0/9] [v2] System Calls for Memory Protection Keys Dave Hansen
2016-06-07 20:47 ` [PATCH 6/9] x86, pkeys: add pkey set/get syscalls Dave Hansen
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