Re: [PATCH] KVM: s390: Fix potential spectre warnings

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On 17.04.19 16:23, Eric Farman wrote:
> 
> 
> On 4/17/19 3:49 AM, David Hildenbrand wrote:
>> On 17.04.19 02:54, Eric Farman wrote:
>>> Fix some warnings from smatch:
>>>
>>> arch/s390/kvm/interrupt.c:2310 get_io_adapter() warn: potential spectre issue 'kvm->arch.adapters' [r] (local cap)
>>> arch/s390/kvm/interrupt.c:2341 register_io_adapter() warn: potential spectre issue 'dev->kvm->arch.adapters' [w]
>>>
>>> Signed-off-by: Eric Farman <farman@xxxxxxxxxxxxx>
>>> ---
>>> A recent patch from Paolo [1] acted as a reminder (thanks, Christian!)
>>> that I had one for the s390 KVM code after some code reviews [2].
>>> Let's clean that up.
>>>
>>> [1] https://patchwork.kernel.org/patch/10895463/
>>> [2] https://patchwork.kernel.org/patch/10788565/#22484223
>>> ---
>>>   arch/s390/kvm/interrupt.c | 11 +++++++++--
>>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
>>> index 82162867f378..bfd55ad34a3e 100644
>>> --- a/arch/s390/kvm/interrupt.c
>>> +++ b/arch/s390/kvm/interrupt.c
>>> @@ -14,6 +14,7 @@
>>>   #include <linux/kvm_host.h>
>>>   #include <linux/hrtimer.h>
>>>   #include <linux/mmu_context.h>
>>> +#include <linux/nospec.h>
>>>   #include <linux/signal.h>
>>>   #include <linux/slab.h>
>>>   #include <linux/bitmap.h>
>>> @@ -2307,6 +2308,7 @@ static struct s390_io_adapter *get_io_adapter(struct kvm *kvm, unsigned int id)
>>>   {
>>>   	if (id >= MAX_S390_IO_ADAPTERS)
>>>   		return NULL;
>>> +	id = array_index_nospec(id, MAX_S390_IO_ADAPTERS);
>>>   	return kvm->arch.adapters[id];
>>
>> return kvm->arch.adapters[array_index_nospec(id, MAX_S390_IO_ADAPTERS)];
>>
>> should exactly fit into a single line if I am not wrong.
> 
> Yeah, just.  As Paolo pointed out, that's not common usage.  Though of 
> the four other hits I see, only one of them is the same as this 
> instance, in that "id" is passed as a variable and then we immediately 
> return with an array entry (even if NULL) rather than doing something 
> else in that function.  So maybe all-in-one-line here is a little cleaner.
> 
>>
>>>   }
>>>   
>>> @@ -2320,8 +2322,13 @@ static int register_io_adapter(struct kvm_device *dev,
>>>   			   (void __user *)attr->addr, sizeof(adapter_info)))
>>>   		return -EFAULT;
>>>   
>>> -	if ((adapter_info.id >= MAX_S390_IO_ADAPTERS) ||
>>> -	    (dev->kvm->arch.adapters[adapter_info.id] != NULL))
>>> +	if (adapter_info.id >= MAX_S390_IO_ADAPTERS)
>>> +		return -EINVAL;
>>> +
>>> +	adapter_info.id = array_index_nospec(adapter_info.id,
>>> +					     MAX_S390_IO_ADAPTERS);
>>
>> I dislike that we are modifying adapter_info here. Can you use a local
>> variable instead?
> 
> I guess, but adapter_info is a local variable too.  So sanitization this 
> way seems fine to me.  But if you dislike it more than I don't care, 
> I'll add another local variable.  :)


Oh right, I was confused, sorry. All fine.

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

-- 

Thanks,

David / dhildenb



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