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ARM: 7735/2: Preserve the user r/w register TPIDRURW on context switch and fork

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Since commit 6a1c53124a 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>
This commit is contained in:
André Hentschel
2013-06-18 23:23:26 +01:00
committed by Russell King
parent 4a1b573346
commit a4780adeef
6 changed files with 37 additions and 20 deletions
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4
arch/arm/kernel/process.c
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@@ -39,6 +39,7 @@
#include <asm/thread_notify.h>
#include <asm/stacktrace.h>
#include <asm/mach/time.h>
#include <asm/tls.h>
#ifdef CONFIG_CC_STACKPROTECTOR
#include <linux/stackprotector.h>
@@ -343,7 +344,8 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start,
clear_ptrace_hw_breakpoint(p);
if (clone_flags & CLONE_SETTLS)
thread->tp_value = childregs->ARM_r3;
thread->tp_value[0] = childregs->ARM_r3;
thread->tp_value[1] = get_tpuser();
thread_notify(THREAD_NOTIFY_COPY, thread);