From: H. Peter Anvin Date: Fri, 23 Apr 2010 23:17:40 +0000 (-0700) Subject: x86-64: Clear a 64-bit FS/GS base on fork if selector is nonzero X-Git-Tag: firefly_0821_release~10186^2~1676 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=e620234b3ec62cedcdc3a8c53ed50facd4392cb3;p=firefly-linux-kernel-4.4.55.git x86-64: Clear a 64-bit FS/GS base on fork if selector is nonzero commit 7ce5a2b9bb2e92902230e3121d8c3047fab9cb47 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 Signed-off-by: H. Peter Anvin LKML-Reference: <4BD1E061.8030605@zytor.com> Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 6eabe9004126..868fdb407bb9 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -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);