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SubjectBUG: optimized kprobes illegal instructions in v4.19 stable kernels
Hi,

I notice this commit as a possible culprit of the illegal instructions my lttng
users are noticing on arm32 when using kprobes on a v4.19.13 Linux kernel
in a Yocto environment [1]. They were able to reproduce the issue with perf
as well.

commit e46daee53bb50bde38805f1823a182979724c229
Author: Kees Cook <keescook@chromium.org>
Date: Tue Oct 30 22:12:56 2018 +0100

ARM: 8806/1: kprobes: Fix false positive with FORTIFY_SOURCE

I *think* the intent there was to do

- memcpy(code, &optprobe_template_entry,
+ memcpy(code, (unsigned long *)&optprobe_template_entry,

But if you look at the commit, the "&" seems to have been stripped away,
which happens to change the behavior significantly.

Has this change ever been runtime-tested ?

It has been backported to:
- 4.19 stable as commit 3fe0c68aea21
- 4.14 stable as commit f9e0bc710347

Thanks,

Mathieu

[1] https://bugs.lttng.org/issues/1174

--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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