Indirect branch tracking for Intel CPUs

Posted Mar 31, 2022 20:25 UTC (Thu) by donald.buczek (subscriber, #112892)
In reply to: Indirect branch tracking for Intel CPUs by mb
Parent article: Indirect branch tracking for Intel CPUs

I think, kallsym_lookup_name itself is no longer exported. But you can work around that, too.

There are legitimate reasons to call a non-exported kernel function from a module. E.g. when you create a module to install a ftrace-based wrapper around a kernel function with a security problem because you can't immediately reboot into a fixed kernel for one reason or another and you are not prepared for live patching.

We recently had to do that [1] and needed to work around a missing kallsym_lookup_name, which we did with register_kprobe.

The attempt of the kernel to restrict modules reminds me of DRM. You don't really succeed, bad guys work around anyway, but you make life harder for legitimate users.

[1]: https://github.molgen.mpg.de/mariux64/fix-lpp/blob/main/f...

Indirect branch tracking for Intel CPUs

Posted Apr 2, 2022 1:45 UTC (Sat) by developer122 (guest, #152928) [Link] (1 responses)

On philosophical grounds I also half-object to the indifference about what licence that code is under. There's no love for fellow copyleft brethren who aren't specifically GPL. (despite Torvalds' insistence on getting changes back being his real only aim)

Half-object because there would be *some* maintenance burden to making changes for out of tree code. The kernel already has to periodically sync against other upstream projects whose code it uses.

Indirect branch tracking for Intel CPUs

Posted Apr 6, 2022 16:34 UTC (Wed) by immibis (subscriber, #105511) [Link]

All derivative works of the kernel must be GPLv2 - that's how the GPL works. AFAIK Linus's opinion is that if you only use non-GPL-marked exported functions - functions you might expect to find in any kernel - then your module is not a derivative work of Linux in particular, but GPL exports are functions that are sufficiently entangled with Linux in particular that you can't reasonably claim your driver is not derived from Linux.