Messages in this thread | | | Date | Fri, 30 Apr 2010 12:52:31 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 1/4] KVM MMU: fix race in invlpg code |
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On 04/30/2010 12:00 PM, Xiao Guangrong wrote: > It has race in invlpg code, like below sequences: > > A: hold mmu_lock and get 'sp' > B: release mmu_lock and do other things > C: hold mmu_lock and continue use 'sp' > > if other path freed 'sp' in stage B, then kernel will crash > > This patch checks 'sp' whether lived before use 'sp' in stage C >
> Signed-off-by: Xiao Guangrong<xiaoguangrong@cn.fujitsu.com> > --- > arch/x86/kvm/paging_tmpl.h | 18 +++++++++++++++++- > 1 files changed, 17 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h > index 624b38f..641d844 100644 > --- a/arch/x86/kvm/paging_tmpl.h > +++ b/arch/x86/kvm/paging_tmpl.h > @@ -462,11 +462,15 @@ out_unlock: > > static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva) > { > - struct kvm_mmu_page *sp = NULL; > + struct kvm_mmu_page *sp = NULL, *s; > struct kvm_shadow_walk_iterator iterator; > + struct hlist_head *bucket; > + struct hlist_node *node, *tmp; > gfn_t gfn = -1; > u64 *sptep = NULL, gentry; > int invlpg_counter, level, offset = 0, need_flush = 0; > + unsigned index; > + bool live = false; > > spin_lock(&vcpu->kvm->mmu_lock); > > @@ -519,10 +523,22 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva) > > mmu_guess_page_from_pte_write(vcpu, gfn_to_gpa(gfn) + offset, gentry); > spin_lock(&vcpu->kvm->mmu_lock); > + index = kvm_page_table_hashfn(gfn); > + bucket =&vcpu->kvm->arch.mmu_page_hash[index]; > + hlist_for_each_entry_safe(s, node, tmp, bucket, hash_link) > + if (s == sp) { >
At this point, sp might have been freed and re-allocated, now pointing at something completely different. So need to check role etc.
Alternatively, increase root_count. Then sp is guaranteed to be live (though it may have role.invalid set).
> + live = true; > + break; > + } > + > + if (!live) > + goto unlock_exit; > + > if (atomic_read(&vcpu->kvm->arch.invlpg_counter) == invlpg_counter) { > ++vcpu->kvm->stat.mmu_pte_updated; > FNAME(update_pte)(vcpu, sp, sptep,&gentry); > } > +unlock_exit: > spin_unlock(&vcpu->kvm->mmu_lock); > mmu_release_page_from_pte_write(vcpu); > } >
-- Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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