x86: Don't leak 64-bit kernel register values to 32-bit processes

x86: Don't leak 64-bit kernel register values to 32-bit processes

commit 24e35800cdc4350fc34e2bed37b608a9e13ab3b6 upstream

x86: Don't leak 64-bit kernel register values to 32-bit processes

While 32-bit processes can't directly access R8...R15, they can
gain access to these registers by temporarily switching themselves
into 64-bit mode.

Therefore, registers not preserved anyway by called C functions
(i.e. R8...R11) must be cleared prior to returning to user mode.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <4AC34D73020000780001744A@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>