From 886d462b0c92357a2f0ca0fc19f5877efbb1f638 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Mon, 30 Jan 2012 20:21:42 +0100 Subject: ARM: 7306/1: vfp: flush thread hwstate before restoring context from sigframe commit 2af276dfb1722e97b190bd2e646b079a2aa674db upstream. Following execution of a signal handler, we currently restore the VFP context from the ucontext in the signal frame. This involves copying from the user stack into the current thread's vfp_hard_struct and then flushing the new data out to the hardware registers. This is problematic when using a preemptible kernel because we could be context switched whilst updating the vfp_hard_struct. If the current thread has made use of VFP since the last context switch, the VFP notifier will copy from the hardware registers into the vfp_hard_struct, overwriting any data that had been partially copied by the signal code. Disabling preemption across copy_from_user calls is a terrible idea, so instead we move the VFP thread flush *before* we update the vfp_hard_struct. Since the flushing is performed lazily, this has the effect of disabling VFP and clearing the CPU's VFP state pointer, therefore preventing the thread from being updated with stale data on the next context switch. Tested-by: Peter Maydell Signed-off-by: Will Deacon Signed-off-by: Russell King Signed-off-by: Greg Kroah-Hartman --- arch/arm/kernel/signal.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) (limited to 'arch/arm/kernel') diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c index 0340224..9e617bd 100644 --- a/arch/arm/kernel/signal.c +++ b/arch/arm/kernel/signal.c @@ -227,6 +227,8 @@ static int restore_vfp_context(struct vfp_sigframe __user *frame) if (magic != VFP_MAGIC || size != VFP_STORAGE_SIZE) return -EINVAL; + vfp_flush_hwstate(thread); + /* * Copy the floating point registers. There can be unused * registers see asm/hwcap.h for details. @@ -251,9 +253,6 @@ static int restore_vfp_context(struct vfp_sigframe __user *frame) __get_user_error(h->fpinst, &frame->ufp_exc.fpinst, err); __get_user_error(h->fpinst2, &frame->ufp_exc.fpinst2, err); - if (!err) - vfp_flush_hwstate(thread); - return err ? -EFAULT : 0; } -- cgit v1.1