linux-kernel - Re: [PATCH] Avoid overflows in kernel/time.c

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]

Date:	Thu, 06 Dec 2007 16:22:05 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Adrian Bunk <bunk@...nel.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Avoid overflows in kernel/time.c

Adrian Bunk wrote:
> On Thu, Nov 29, 2007 at 04:19:51PM -0800, H. Peter Anvin wrote:
>   
>> When the conversion factor between jiffies and milli- or microseconds
>> is not a single multiply or divide, as for the case of HZ == 300, we
>> currently do a multiply followed by a divide.  The intervening
>> result, however, is subject to overflows, especially since the
>> fraction is not simplified (for HZ == 300, we multiply by 300 and
>> divide by 1000).
>> ...
>>  kernel/Makefile     |    8 +++
>>  kernel/time.c       |   29 +++++++++---
>>  kernel/timeconst.bc |  123 +++++++++++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 152 insertions(+), 8 deletions(-)
>>  create mode 100644 kernel/timeconst.bc
>> ...
>>     
>
> I have read the hep text, but are the advantages of HZ == 300 really 
> visible or was this more theoretical?
>
> In the latter case, we might remove the HZ == 300 choice instead.
>   

300 is useful for video applications, since its a multiple of both 50
and 60Hz.  Tickless may make this less relevent though.

    J
--
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/