RE: NULL pointer dereference in igen6_probe - 6.16-rc2

[Zhuo, Qiuxu]

> From: Borislav Petkov <bp@xxxxxxxxx>
> [...]
> > Reverting 'cfg' in this igen6_edac driver to non-const, allowing it to
> > be set with the actual number of detected memory controllers seems
> reasonable.
> 
> Question is: is that something the driver should allow? Detecting more

In the igen6_edac driver, when notified of the memory errors, it checks all 
the memory controllers specified by 'cfg->num_imc' to identify the source 
of the error. 

Either checking if imc->window == NULL (indicating null MMIO for absent 
memory controllers) before each usage point, or updating 'cfg->num_imc' to
reflect the real present memory controllers should fix the issue.  The latter
one is simpler.

> memory controllers but enabling less. How can that even happen?
> 

The maximum number of detected memory controllers is bounded
by the macro NUM_IMC [1]. This value is what we know as the maximum 
possible value now.

[1] https://github.com/torvalds/linux/blob/master/drivers/edac/igen6_edac.c#L1324

> > After that then applying Boris' fix above is the simplest way to
> > resolve the issue. 😊
> 
> Right, just prepare a proper patch, please, so that Marek can test and confirm.
> 

OK. 
I'll make a patch for Marek to test first. 
Thanks Boris.

- Qiuxu