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From: Scott Long <scottl@samsco.org>
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To: "K. Macy" <kmacy@freebsd.org>
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Cc: Luigi Rizzo <rizzo@iet.unipi.it>, current@freebsd.org
Subject: Re: fast/syscall-free gettimeofday ?
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If this was to be extended with cached global syscall information like =
gettimeofday, would we want that to be in a separate page that is marked =
non-executable?  Is there any way to trick the kernel into leaking =
arbitrary (and thus executable) code?  Also, would it matter for jails?  =
Per-process info like getpid would obviously have to be a separate =
per-process page.

Scott

On Jun 14, 2011, at 10:08 AM, K. Macy wrote:

> http://svnweb.freebsd.org/base/head/sys/sys/imgact.h
>=20
> kib added rudimentary support for this in January
>=20
> On Tue, Jun 14, 2011 at 6:11 PM, Luigi Rizzo <rizzo@iet.unipi.it> =
wrote:
>> there were discussions at some point on an imprecise but
>> fast implementations of gettimeofday() that would not require
>> a system call (perhaps mmapping some memory region which
>> is opportunistically updated).
>>=20
>> Does anyone remember what happened about that ?
>>=20
>> Otherwise, is there any place in the kernel where i can fetch
>> a struct timeval which is not off by more than, say 1 tick ?
>>=20
>> cheers
>> luigi
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>>=20
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