ARM: 7307/1: vfp: fix ptrace regset modification race
In a preemptible kernel, vfp_set() can be preempted, causing the hardware VFP context to be switched while the thread vfp state is being read and modified. This leads to a race condition which can cause the thread vfp state to become corrupted if lazy VFP context save occurs due to preemption in between the time thread->vfpstate is read and the time the modified state is written back. This may occur if preemption occurs during the execution of a ptrace() call which modifies the VFP register state of a thread. Such instances should be very rare in most realistic scenarios -- none has been reported, so far as I am aware. Only uniprocessor systems should be affected, since VFP context save is not currently lazy in SMP kernels. The problem was introduced by my earlier patch migrating to use regsets to implement ptrace. This patch does a vfp_sync_hwstate() before reading thread->vfpstate, to make sure that the thread's VFP state is not live in the hardware registers while the registers are modified. Thanks to Will Deacon for spotting this. Cc: stable <stable@vger.kernel.org> Signed-off-by:Dave Martin <dave.martin@linaro.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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