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Message-ID: <CAGXu5jKsj+_O-NAATco6Ln6DLdcA+BC8_zd9DVfLNRa3jL+E=w@mail.gmail.com>
Date: Wed, 9 Jan 2019 14:59:46 -0800
From: Kees Cook <keescook@...omium.org>
To: Jason Yan <yanaijie@...wei.com>
Cc: Jann Horn <jannh@...gle.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, zhaohongjiang@...wei.com,
miaoxie@...wei.com, Li Bin <huawei.libin@...wei.com>,
Wei Yongjun <weiyongjun1@...wei.com>
Subject: Re: [PATCH] usercopy: skip the check if not a real usercopy
On Tue, Jan 8, 2019 at 6:26 PM Jason Yan <yanaijie@...wei.com> wrote:
> It's very easy to reproduce in qemu using my config with v4.20. Please
> refer to the attachment.
>
> I did some debug and found that check_object_size() did not stuck but
> check_object_size() sometimes takes more than 30 milliseconds, and
> ftrace will call __probe_kernel_write() thousands of times, which makes
> the whole process stuck for more than 20 seconds.
30ms is still WAY too long. :)
> [yanaijie@138 linux]$ ./scripts/faddr2line vmlinux
> __check_object_size+0x5/0x460
> __check_object_size+0x5/0x460:
> __check_object_size at mm/usercopy.c:254
> [yanaijie@138 linux]$
For me, that's the entry to __check_object_size (the line with "{").
Is that what you see too?
Perhaps this is poor interaction with tracing? Does marking
__check_object_size with "notrace" help?
--
Kees Cook
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