[lttng-dev] optimized kprobes illegal instructions in v4.19 stable kernels

[David Laight]

From: Mathieu Desnoyers
> Sent: 04 February 2019 19:15
> 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 at 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.

Which is why you shouldn't add casts to shut up compiler warnings ....

	David

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