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Nothing has to modify this after init.
But of course there is code which unconditionally masks
xfeatures_mask_all on CPU hotplug. This goes unnoticed during boot
hotplug because at that point the variable is still RW mapped.
This is broken in several ways:
1) Masking this in post init CPU hotplug means that any
modification of this state goes unnoticed until actual hotplug
happens.
2) If that ever happens then these bogus feature bits are already
populated all over the place and the system is in inconsistent state
vs. the compacted XSTATE offsets. If at all then this has to panic the
machine because the inconsistency cannot be undone anymore.
Make this a one-time paranoia check in xstate init code and disable
xsave when this happens.
Reported-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121451.712803952@linutronix.de
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