2016-03-22 16:40:18

by Paolo Bonzini

Subject: [PATCH] KVM: page_track: fix access to NULL slot

This happens when doing the reboot test from virt-tests:

[ 131.833653] BUG: unable to handle kernel NULL pointer dereference at (null)
[ 131.842461] IP: [<ffffffffa0950087>] kvm_page_track_is_active+0x17/0x60 [kvm]
[ 131.850500] PGD 0
[ 131.852763] Oops: 0000 [#1] SMP
[ 132.007188] task: ffff880075fbc500 ti: ffff880850a3c000 task.ti: ffff880850a3c000
[ 132.138891] Call Trace:
[ 132.141639] [<ffffffffa092bd11>] page_fault_handle_page_track+0x31/0x40 [kvm]
[ 132.149732] [<ffffffffa093380f>] paging64_page_fault+0xff/0x910 [kvm]
[ 132.172159] [<ffffffffa092c734>] kvm_mmu_page_fault+0x64/0x110 [kvm]
[ 132.179372] [<ffffffffa06743c2>] handle_exception+0x1b2/0x430 [kvm_intel]
[ 132.187072] [<ffffffffa067a301>] vmx_handle_exit+0x1e1/0xc50 [kvm_intel]
...

Cc: Xiao Guangrong <[email protected]>
Fixes: 3d0c27ad6ee465f174b09ee99fcaf189c57d567a
Signed-off-by: Paolo Bonzini <[email protected]>
---
arch/x86/kvm/page_track.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/page_track.c b/arch/x86/kvm/page_track.c
index 11f76436f74f..b431539c3714 100644
--- a/arch/x86/kvm/page_track.c
+++ b/arch/x86/kvm/page_track.c
@@ -142,12 +142,17 @@ void kvm_slot_page_track_remove_page(struct kvm *kvm,
bool kvm_page_track_is_active(struct kvm_vcpu *vcpu, gfn_t gfn,
enum kvm_page_track_mode mode)
{
- struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
- int index = gfn_to_index(gfn, slot->base_gfn, PT_PAGE_TABLE_LEVEL);
+ struct kvm_memory_slot *slot;
+ int index;

if (WARN_ON(!page_track_mode_is_valid(mode)))
return false;

+ slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
+ if (!slot)
+ return false;
+
+ index = gfn_to_index(gfn, slot->base_gfn, PT_PAGE_TABLE_LEVEL);
return !!ACCESS_ONCE(slot->arch.gfn_track[mode][index]);
}

--
1.8.3.1

2016-03-23 02:22:36

by Xiao Guangrong

Subject: Re: [PATCH] KVM: page_track: fix access to NULL slot

On 03/23/2016 12:40 AM, Paolo Bonzini wrote:
> This happens when doing the reboot test from virt-tests:
>
> [ 131.833653] BUG: unable to handle kernel NULL pointer dereference at (null)
> [ 131.842461] IP: [<ffffffffa0950087>] kvm_page_track_is_active+0x17/0x60 [kvm]
> [ 131.850500] PGD 0
> [ 131.852763] Oops: 0000 [#1] SMP
> [ 132.007188] task: ffff880075fbc500 ti: ffff880850a3c000 task.ti: ffff880850a3c000
> [ 132.138891] Call Trace:
> [ 132.141639] [<ffffffffa092bd11>] page_fault_handle_page_track+0x31/0x40 [kvm]
> [ 132.149732] [<ffffffffa093380f>] paging64_page_fault+0xff/0x910 [kvm]
> [ 132.172159] [<ffffffffa092c734>] kvm_mmu_page_fault+0x64/0x110 [kvm]
> [ 132.179372] [<ffffffffa06743c2>] handle_exception+0x1b2/0x430 [kvm_intel]
> [ 132.187072] [<ffffffffa067a301>] vmx_handle_exit+0x1e1/0xc50 [kvm_intel]
> ...

Thank you for fixing it, Paolo!

Reviewed-by: Xiao Guangrong <[email protected]>