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Commit 7ce5a2b9 authored by H. Peter Anvin's avatar H. Peter Anvin
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x86-64: Clear a 64-bit FS/GS base on fork if selector is nonzero 



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: default avatarSamuel Thibault <samuel.thibault@inria.fr>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
LKML-Reference: <4BD1E061.8030605@zytor.com>
Cc: <stable@kernel.org>
parent ae7c9b70

arch/x86/kernel/process_64.c

+2 −2
Original line number Diff line number Diff line
@@ -276,12 +276,12 @@ 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;

	p->thread.io_bitmap_ptr = NULL;



	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);