From a2b7861bb33b2538420bb5d8554153484d3f961f Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 3 Oct 2017 21:36:51 +0800 Subject: kvm/x86: Avoid async PF preempting the kernel incorrectly MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Currently, in PREEMPT_COUNT=n kernel, kvm_async_pf_task_wait() could call schedule() to reschedule in some cases. This could result in accidentally ending the current RCU read-side critical section early, causing random memory corruption in the guest, or otherwise preempting the currently running task inside between preempt_disable and preempt_enable. The difficulty to handle this well is because we don't know whether an async PF delivered in a preemptible section or RCU read-side critical section for PREEMPT_COUNT=n, since preempt_disable()/enable() and rcu_read_lock/unlock() are both no-ops in that case. To cure this, we treat any async PF interrupting a kernel context as one that cannot be preempted, preventing kvm_async_pf_task_wait() from choosing the schedule() path in that case. To do so, a second parameter for kvm_async_pf_task_wait() is introduced, so that we know whether it's called from a context interrupting the kernel, and the parameter is set properly in all the callsites. Cc: "Paul E. McKenney" Cc: Peter Zijlstra Cc: Wanpeng Li Cc: stable@vger.kernel.org Signed-off-by: Boqun Feng Signed-off-by: Radim Krčmář --- arch/x86/kernel/kvm.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index e675704fa6f7..8bb9594d0761 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -117,7 +117,11 @@ static struct kvm_task_sleep_node *_find_apf_task(struct kvm_task_sleep_head *b, return NULL; } -void kvm_async_pf_task_wait(u32 token) +/* + * @interrupt_kernel: Is this called from a routine which interrupts the kernel + * (other than user space)? + */ +void kvm_async_pf_task_wait(u32 token, int interrupt_kernel) { u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS); struct kvm_task_sleep_head *b = &async_pf_sleepers[key]; @@ -140,8 +144,10 @@ void kvm_async_pf_task_wait(u32 token) n.token = token; n.cpu = smp_processor_id(); - n.halted = is_idle_task(current) || preempt_count() > 1 || - rcu_preempt_depth(); + n.halted = is_idle_task(current) || + (IS_ENABLED(CONFIG_PREEMPT_COUNT) + ? preempt_count() > 1 || rcu_preempt_depth() + : interrupt_kernel); init_swait_queue_head(&n.wq); hlist_add_head(&n.link, &b->list); raw_spin_unlock(&b->lock); @@ -269,7 +275,7 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code) case KVM_PV_REASON_PAGE_NOT_PRESENT: /* page is swapped out by the host. */ prev_state = exception_enter(); - kvm_async_pf_task_wait((u32)read_cr2()); + kvm_async_pf_task_wait((u32)read_cr2(), !user_mode(regs)); exception_exit(prev_state); break; case KVM_PV_REASON_PAGE_READY: -- cgit v1.2.3