netdev - Re: [PATCH net-next 1/2] net: Header length compution function

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:	Wed, 30 Jul 2014 18:34:10 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	amirv@...lanox.com, alexander.h.duyck@...el.com,
	netdev@...r.kernel.org, ogerlitz@...lanox.com,
	yevgenyp@...lanox.com, idos@...lanox.com
Subject: Re: [PATCH net-next 1/2] net: Header length compution function

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 30 Jul 2014 09:00:44 +0200

> This adds quite large number of conditional jumps, as
> skb_header_pointer() is heavily used in the stack.

There is only one, in __skb_header_pointer(), testing "!skb" when we
have to take the slow path of copying from a non-linear area.

The NULL check could even be moved into skb_copy_bits() so that it
would not be inlined.  It should be unlikely() (or even WARN_ON()),
and thus terribly easily to be predicted properly all the time.

We could even pass around a "sentinel" global const SKB for these
cases that would simply make skb_copy_bits() return immediately (just
having skb->len == 0 would do the trick) even if we accidently got
there with one.

Then there would be no extra conditional jumps.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html