5b781c7e31
For mysterious historical reasons, struct user_desc doesn't indicate
whether segments are accessed. set_thread_area() has always programmed
segments as non-accessed, so the first write will set the accessed bit.
This will fault if the GDT is read-only.
Fix it by making TLS segments start out accessed.
If this ends up breaking something, we could, in principle, leave TLS
segments non-accessed and fix them up when we get the page fault. I'd be
surprised, though -- AFAIK all the nasty legacy segmented programs (DOSEMU,
Wine, things that run on DOSEMU and Wine, etc.) do their nasty segmented
things using the LDT and not the GDT. I assume this is mainly because old
OSes (Linux and otherwise) didn't historically provide APIs to do nasty
things in the GDT.
Fixes: 45fc8757d1d2 ("x86: Make the GDT remapping read-only on 64-bit")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Garnier <thgarnie@google.com>
Link: http://lkml.kernel.org/r/62b7748542df0164af7e0a5231283b9b13858c45.1489900519.git.luto@kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.