4e8e4313cf
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
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.