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authorWill Deacon <will.deacon@arm.com>2012-04-27 12:45:07 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2012-04-28 11:01:30 +0100
commit6a1c53124aa161eb624ce7b1e40ade728186d34c (patch)
treede0b665b261df06bede794a469f9aa931af39d9d /arch/arm/kernel
parent14904927fcef6bb881fd995b478a0d2e700c1818 (diff)
downloadvexpress-lsk-6a1c53124aa161eb624ce7b1e40ade728186d34c.tar.gz
ARM: 7403/1: tls: remove covert channel via TPIDRURW
TPIDRURW is a user read/write register forming part of the group of thread registers in more recent versions of the ARM architecture (~v6+). Currently, the kernel does not touch this register, which allows tasks to communicate covertly by reading and writing to the register without context-switching affecting its contents. This patch clears TPIDRURW when TPIDRURO is updated via the set_tls macro, which is called directly from __switch_to. Since the current behaviour makes the register useless to userspace as far as thread pointers are concerned, simply clearing the register (rather than saving and restoring it) will not cause any problems to userspace. Cc: stable@vger.kernel.org Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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