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a0e6e0831c
modify_ldt(2) leaves the old LDT mapped after switching over to the new
one. The old LDT gets freed and the pages can be re-used.
Leaving the mapping in place can have security implications. The mapping is
present in the userspace page tables and Meltdown-like attacks can read
these freed and possibly reused pages.
It's relatively simple to fix: unmap the old LDT and flush TLB before
freeing the old LDT memory.
This further allows to avoid flushing the TLB in map_ldt_struct() as the
slot is unmapped and flushed by unmap_ldt_struct() or has never been mapped
at all.
[ tglx: Massaged changelog and removed the needless line breaks ]
Fixes: f55f0501cb ("x86/pti: Put the LDT in its own PGD if PTI is on")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: dave.hansen@linux.intel.com
Cc: luto@kernel.org
Cc: peterz@infradead.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: bhe@redhat.com
Cc: willy@infradead.org
Cc: linux-mm@kvack.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181026122856.66224-3-kirill.shutemov@linux.intel.com
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.