From 7ce5a2b9bb2e92902230e3121d8c3047fab9cb47 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Fri, 23 Apr 2010 16:17:40 -0700 Subject: [PATCH] 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: Samuel Thibault Signed-off-by: H. Peter Anvin LKML-Reference: <4BD1E061.8030605@zytor.com> Cc: --- arch/x86/kernel/process_64.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index dc9690b4c4cc..17cb3295cbf7 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -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); -- 2.20.1