From 247f4993a5974e6759606c4d380748eecfd273ff Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Mon, 30 Jan 2012 20:22:28 +0100 Subject: [PATCH] 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 Signed-off-by: Dave Martin Signed-off-by: Will Deacon Signed-off-by: Russell King --- arch/arm/kernel/ptrace.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index e1d5e1929fbd..d001be4e0ce1 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -699,10 +699,13 @@ static int vfp_set(struct task_struct *target, { int ret; struct thread_info *thread = task_thread_info(target); - struct vfp_hard_struct new_vfp = thread->vfpstate.hard; + struct vfp_hard_struct new_vfp; const size_t user_fpregs_offset = offsetof(struct user_vfp, fpregs); const size_t user_fpscr_offset = offsetof(struct user_vfp, fpscr); + vfp_sync_hwstate(thread); + new_vfp = thread->vfpstate.hard; + ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &new_vfp.fpregs, user_fpregs_offset, @@ -723,7 +726,6 @@ static int vfp_set(struct task_struct *target, if (ret) return ret; - vfp_sync_hwstate(thread); thread->vfpstate.hard = new_vfp; vfp_flush_hwstate(thread); -- 2.30.2