ARM: 7735/2: Preserve the user r/w register TPIDRURW on context switch and fork
authorAndré Hentschel <nerv@dawncrow.de>
Tue, 18 Jun 2013 22:23:26 +0000 (23:23 +0100)
committerRussell King <rmk+kernel@arm.linux.org.uk>
Mon, 24 Jun 2013 14:21:59 +0000 (15:21 +0100)
commita4780adeefd042482f624f5e0d577bf9cdcbb760
treeead0e79b4f797a26cc30fc1596ada6fd6da5daf6
parent4a1b573346ee0d64d95beb78d49a5bbb574e6c6a
ARM: 7735/2: Preserve the user r/w register TPIDRURW on context switch and fork

Since commit 6a1c53124aa1 the user writeable TLS register was zeroed to
prevent it from being used as a covert channel between two tasks.

There are more and more applications coming to Windows RT,
Wine could support them, but mostly they expect to have
the thread environment block (TEB) in TPIDRURW.

This patch preserves that register per thread instead of clearing it.
Unlike the TPIDRURO, which is already switched, the TPIDRURW
can be updated from userspace so needs careful treatment in the case that we
modify TPIDRURW and call fork(). To avoid this we must always read
TPIDRURW in copy_thread.

Signed-off-by: André Hentschel <nerv@dawncrow.de>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
arch/arm/include/asm/thread_info.h
arch/arm/include/asm/tls.h
arch/arm/kernel/entry-armv.S
arch/arm/kernel/process.c
arch/arm/kernel/ptrace.c
arch/arm/kernel/traps.c