> > Runtime disabling kexec looks better than at cmpile time, esp for
> > distros. While from above patch, making using of kexec_load_disabled
> > to achive the runtime disabling may not be so good. Because we have a
> > front door to enable it through:
> >
> > /proc/sys/kernel/kexec_load_disabled
> 
> AFAIU it can't be enabled via this sysctl because the handler for it expects
> only 1 to be written to it:
> 
>       2                 .proc_handler   = proc_dointvec_minmax,
> 
>       1                 .extra1         = SYSCTL_ONE,
> 
>    994                  .extra2         = SYSCTL_ONE,
> 

This is also my understanding.  

The documentation also says once it is turned to disable we cannot turn back again:

kexec_load_disable
===================

A toggle indicating if the syscalls ``kexec_load`` and
``kexec_file_load`` have been disabled.
This value defaults to 0 (false: ``kexec_*load`` enabled), but can be
set to 1 (true: ``kexec_*load`` disabled).
Once true, kexec can no longer be used, and the toggle cannot be set
back to false.
......

On 01/31/24 at 01:07pm, Huang, Kai wrote:
> > > Runtime disabling kexec looks better than at cmpile time, esp for
> > > distros. While from above patch, making using of kexec_load_disabled
> > > to achive the runtime disabling may not be so good. Because we have a
> > > front door to enable it through:
> > >
> > > /proc/sys/kernel/kexec_load_disabled
> > 
> > AFAIU it can't be enabled via this sysctl because the handler for it expects
> > only 1 to be written to it:
> > 
> >       2                 .proc_handler   = proc_dointvec_minmax,
> > 
> >       1                 .extra1         = SYSCTL_ONE,
> > 
> >    994                  .extra2         = SYSCTL_ONE,
> > 
> 
> This is also my understanding.  
> 
> The documentation also says once it is turned to disable we cannot turn back again:
> 
> kexec_load_disable
> ===================
> 
> A toggle indicating if the syscalls ``kexec_load`` and
> ``kexec_file_load`` have been disabled.
> This value defaults to 0 (false: ``kexec_*load`` enabled), but can be
> set to 1 (true: ``kexec_*load`` disabled).
> Once true, kexec can no longer be used, and the toggle cannot be set
> back to false.

you are quite right, I have never noticed this, thanks.

Then then mentioned patch looks good to me.