linux-kernel - Re: [PATCH v2 7/7] xen/arm: set the system time in Xen via the XENPF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.02.1511101557230.5676@kaball.uk.xensource.com>
Date:	Tue, 10 Nov 2015 15:58:53 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<xen-devel@...ts.xensource.com>, <linux-kernel@...r.kernel.org>,
	<Ian.Campbell@...rix.com>
Subject: Re: [PATCH v2 7/7] xen/arm: set the system time in Xen via the
 XENPF_settime64 hypercall

On Tue, 10 Nov 2015, Arnd Bergmann wrote:
> On Tuesday 10 November 2015 11:57:55 Stefano Stabellini wrote:
> > +       op.u.settime64.nsecs = now.tv_nsec;
> > +       op.u.settime64.system_time = arch_timer_read_counter() * (u64)NSEC_PER_SEC;
> > +       do_div(op.u.settime64.system_time, arch_timer_get_rate());
> 
> NSEC_PER_SEC is a large number, doesn't that multiplication overflow the
> 64-bit system_time variable?

It could be a concern, you are right. I think I can solve this issue and
remove multiple do_divs by calculating nsec_per_tick at initialization
time and use it here and in xen_read_wallclock.


> > +       printk("GTOD: Setting to %llu.%u at %llu\n",
> 
> 				   %llu.%09u
> 
> so you get the leading zeroes.
> 
> > +              op.u.settime64.secs,
> > +              op.u.settime64.nsecs,
> > +              op.u.settime64.system_time);
> > +       (void)HYPERVISOR_platform_op(&op);
> 
> 	Arnd
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/