netdev - RE: [PATCH] net: micro-optimize skb_datagram

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Date: Sun, 16 Jun 2024 21:51:05 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Sagi Grimberg' <sagi@...mberg.me>, kernel test robot
	<oliver.sang@...el.com>, Matthew Wilcox <willy@...radead.org>
CC: "oe-lkp@...ts.linux.dev" <oe-lkp@...ts.linux.dev>, "lkp@...el.com"
	<lkp@...el.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "Eric
 Dumazet" <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>
Subject: RE: [PATCH] net: micro-optimize skb_datagram_iter

From: Sagi Grimberg
> Sent: 16 June 2024 10:24
...
> > [ 13.498663][ T189] EIP: usercopy_abort (mm/usercopy.c:102 (discriminator 12))
> > [   13.499424][  T194] usercopy: Kernel memory exposure attempt detected from kmap (offset 0, size
> 8192)!
> 
> Hmm, not sure I understand exactly why changing kmap() to
> kmap_local_page() expose this,
> but it looks like mm/usercopy does not like size=8192 when copying for
> the skb frag.

Can't a usercopy fault and have to read the page from swap?
So the process can sleep and then be rescheduled on a different cpu?
So you can't use kmap_local_page() here at all.

	David

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