forked from luck/tmp_suning_uos_patched
x86/tls: Forcibly set the accessed bit in TLS segments
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: 45fc8757d1
("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>
This commit is contained in:
parent
2947ba054a
commit
5b781c7e31
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@ -92,10 +92,17 @@ static void set_tls_desc(struct task_struct *p, int idx,
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cpu = get_cpu();
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while (n-- > 0) {
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if (LDT_empty(info) || LDT_zero(info))
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if (LDT_empty(info) || LDT_zero(info)) {
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desc->a = desc->b = 0;
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else
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} else {
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fill_ldt(desc, info);
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/*
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* Always set the accessed bit so that the CPU
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* doesn't try to write to the (read-only) GDT.
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*/
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desc->type |= 1;
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}
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++info;
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++desc;
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}
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