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@xxxxxxxxxxxxxx>
---
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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