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x86-64: Clear a 64-bit FS/GS base on fork if selector is nonzero

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commit 7ce5a2b9bb upstream.

When we do a thread switch, we clear the outgoing FS/GS base if the
corresponding selector is nonzero.  This is taken by __switch_to() as
an entry invariant; it does not verify that it is true on entry.
However, copy_thread() doesn't enforce this constraint, which can
result in inconsistent results after fork().

Make copy_thread() match the behavior of __switch_to().

Reported-and-tested-by: Samuel Thibault <samuel.thibault@inria.fr>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <4BD1E061.8030605@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
H. Peter Anvin
2010-04-23 16:17:40 -07:00
committed by Greg Kroah-Hartman
parent 6dc36b37f6
commit e620234b3e
1 changed files with 2 additions and 3 deletions
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5
arch/x86/kernel/process_64.c
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@@ -295,11 +295,10 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
set_tsk_thread_flag(p, TIF_FORK);
p->thread.fs = me->thread.fs;
p->thread.gs = me->thread.gs;
savesegment(gs, p->thread.gsindex);
p->thread.gs = p->thread.gsindex ? 0 : me->thread.gs;
savesegment(fs, p->thread.fsindex);
p->thread.fs = p->thread.fsindex ? 0 : me->thread.fs;
savesegment(es, p->thread.es);
savesegment(ds, p->thread.ds);