lkml.org 
[lkml]   [2010]   [Apr]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/4] KVM MMU: fix race in invlpg code
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.



\
 
 \ /
  Last update: 2010-04-30 19:27    [W:0.311 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site