On 13/12/2017 04:05, Wanpeng Li wrote:
> 2017-12-13 0:07 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
>> On 12/12/2017 09:57, Wanpeng Li wrote:
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index bc5d853..51e7932 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -4690,7 +4690,10 @@ static int write_emulate(struct kvm_vcpu *vcpu, gpa_t gpa,
>>>
>>> static int write_mmio(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes, void *val)
>>> {
>>> - trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, *(u64 *)val);
>>> + u64 data = 0;
>>> +
>>> + memcpy(&data, val, min(8, bytes));
>>> + trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, data);
>>> return vcpu_mmio_write(vcpu, gpa, bytes, val);
>>> }
>>>
>>>
>>
>> Please do the memcpy in TRACE_EVENT(kvm_mmio)'s TP_fast_assign block.
>> That is done only when the trace event is active.
>
> I still can observe the stack out-of-bounds read warning if keep *(u64
> *)val as the parameter since it has already been dereferenced. So
> maybe we should change the parameter of trace_kvm_mmio() to void *val,
Yes, exactly.
> however, I'm not sure whether it will break the tracepoint ABI which
> this article https://lwn.net/Articles/734039/ "Workload analysis with
> tracing" section pointed out.
No, the tracepoint ABI refers to TP_PROTO, not TP_STRUCT and
TP_fast_assign. Good that you thought about it, though!
Thanks,
Paolo
