From: Felix Fietkau <nbd@openwrt.org>
To: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>
Cc: David Daney <ddaney@caviumnetworks.com>,
netdev@vger.kernel.org,
Lennert Buytenhek <buytenh@wantstofly.org>
Subject: Re: [PATCH] skbuff: align sk_buff::cb to 64 bit
Date: Sat, 30 Jan 2010 00:14:02 +0100 [thread overview]
Message-ID: <4B636BBA.8050300@openwrt.org> (raw)
In-Reply-To: <20100129225404.GA12440@laped.iglesias.mooo.com>
On 2010-01-29 11:54 PM, Edgar E. Iglesias wrote:
> On Fri, Jan 29, 2010 at 02:42:03PM -0800, David Daney wrote:
>> Felix Fietkau wrote:
>> > The alignment requirement for 64-bit load/store instructions on ARM is
>> > implementation defined. Some CPUs (such as Marvell Feroceon) do not
>> > generate an exception, if such an instruction is executed with an
>> > address that is not 64 bit aligned.
>> > In such a case, the Feroceon corrupts adjacent memory, which showed up
>> > in my tests as a crash in the rx path of ath9k that only occured with
>> > CONFIG_XFRM set. This crash happened, because the first field of the
>> > mac80211 rx status info in the cb is an u64, and changing it corrupted
>> > the skb->sp field.
>> >
>> > Signed-off-by: Felix Fietkau <nbd@openwrt.org>
>> > Cc: stable@kernel.org
>> > ---
>> > --- a/include/linux/skbuff.h
>> > +++ b/include/linux/skbuff.h
>> > @@ -329,7 +329,7 @@ struct sk_buff {
>> > * want to keep them across layers you have to do a skb_clone()
>> > * first. This is owned by whoever has the skb queued ATM.
>> > */
>> > - char cb[48];
>> > + char cb[48] __attribute__((aligned(8)));
>> >
> I'd guess the problem is with the accessor to the thing.
> something in the opaque cb ptr its beeing accessed wroingly causing
> overwrites.
Nope, the problem is not with the accessor, I verified that. The start
address of the datastructure that gets put into skb->cb correctly points
at the start of the cb, and it is only aligned to 4 byte, not 8. Also,
this issue only happens on CPUs that do not throw an unaligned exception
for this instruction.
- Felix
next prev parent reply other threads:[~2010-01-29 23:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-29 22:09 [PATCH] skbuff: align sk_buff::cb to 64 bit Felix Fietkau
2010-01-29 22:42 ` David Daney
2010-01-29 22:54 ` Edgar E. Iglesias
2010-01-29 23:14 ` Felix Fietkau [this message]
2010-01-29 23:09 ` Felix Fietkau
2010-01-30 1:41 ` Lennert Buytenhek
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