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From: Daniel Borkmann <daniel@iogearbox.net>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	William Tu <u9012063@gmail.com>
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH] bpf: fix size of copy_to_user in percpu map.
Date: Fri, 29 Jul 2016 09:54:07 +0200	[thread overview]
Message-ID: <579B0B9F.8040805@iogearbox.net> (raw)
In-Reply-To: <20160729064722.GA54517@ast-mbp.thefacebook.com>

On 07/29/2016 08:47 AM, Alexei Starovoitov wrote:
> On Thu, Jul 28, 2016 at 05:42:21PM -0700, William Tu wrote:
>> The total size of value copy_to_user() writes to userspace should
>> be the (current number of cpu) * (value size), instead of
>> num_possible_cpus() * (value size).  Found by samples/bpf/test_maps.c,
>> which always copies 512 byte to userspace, crashing the userspace
>> program stack.
>
> hmm. I'm missing something. The sample code assumes no cpu hutplug,
> so sysconf(_SC_NPROCESSORS_CONF) == num_possible_cpu == num_online_cpu,
> unless there is crazy INIT_ALL_POSSIBLE config option is used.

Are you using ARM by chance? What is the count that you get in
user space and from kernel side?

http://lists.infradead.org/pipermail/linux-arm-kernel/2011-June/054177.html

  reply	other threads:[~2016-07-29  7:54 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-29  0:42 [PATCH] bpf: fix size of copy_to_user in percpu map William Tu
2016-07-29  6:47 ` Alexei Starovoitov
2016-07-29  7:54   ` Daniel Borkmann [this message]
2016-07-29 20:03     ` William Tu
2016-07-30  0:19       ` Daniel Borkmann
2016-07-30  5:23         ` William Tu
2016-07-30  5:34           ` Alexei Starovoitov
2016-07-31 15:25             ` William Tu
2016-08-01 16:07               ` Alexei Starovoitov
2016-08-01 16:30                 ` William Tu
2016-08-12 16:58                   ` William Tu
2016-08-12 23:08                     ` Alexei Starovoitov
2016-08-19  1:38                       ` William Tu
2016-08-24 23:46                         ` William Tu

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